G. Martín Girardi, D. Rana, H. Hoekstra+2 more
AstronomerUsing the FLAMINGO cosmological hydrodynamical simulations, the authors investigate how the halo model should be adapted for density-split galaxy-galaxy lensing analyses. Halos are classified by counts within spherical apertures of radius 1–10 h⁻¹ Mpc. In these simulated samples, the halo mass function and halo bias depend strongly on environment; after density splitting, halo bias is approximately mass-independent. The authors propose an empirical environmental modification to existing halo mass function prescriptions. They also find environmental dependence in the stellar-to-halo-mass relation, conditional stellar mass function, and mass-concentration relation, which they report can be accommodated by existing models. Their inference tests show that neglecting environment biases estimates of the stellar-to-halo-mass relation and satellite fraction. These simulation-based findings motivate revisiting halo-model assumptions for environment-selected samples, including selections by correlated properties such as morphology and color.
PublicThe bending of background light by galaxies can help researchers infer how galaxies relate to their surrounding dark matter halos. This study uses computer simulations, rather than new observations, to test whether the models used to interpret that bending need to account for a galaxy's neighborhood. The simulated halos differ between crowded and sparse regions in their abundance, their clustering relative to matter, and several relationships involving their mass and galaxies. The authors propose a correction for predicting halo abundance in different environments and report that existing models can handle some of the other differences. Their tests find that ignoring environment can distort estimates of the relationship between stellar mass and halo mass, and of the fraction of galaxies that are satellites. The work highlights a potential problem for analyses that group galaxies by neighborhood or by related traits such as shape and color.
Young explorerGalaxies live in neighborhoods: some are crowded, and others have lots of empty space. Scientists used computer-made universes to study the invisible matter around galaxies in these different neighborhoods. In those pretend universes, the neighborhoods made a difference. Ignoring them could give scientists the wrong idea about how galaxies and their invisible matter fit together. The team suggests a way to improve part of the math used to understand how galaxies bend light.
Michele Bianco, Sambit K. Giri, Arghyadeep Basu\orcidlink+4 more
AstronomerThis simulation study tests how scatter in halo mass–star-formation activity affects reionisation. The authors implement stochastic sources in cosmological radiative transfer simulations, calibrating against the high-redshift UV luminosity function observed by JWST and observational constraints on Lyman-continuum leakage. Compared with a deterministic, observationally calibrated model, stochastic star formation shifts ionising emissivity toward lower-mass haloes, fragments the ionisation topology and delays growth of the largest ionised regions. However, when total ionising photon production is matched, global neutral fractions and the 21-cm power spectrum remain nearly indistinguishable despite small morphological differences. A separate unified framework applies source prescriptions from SPICE, FIRE-2 and Thesan to reionisation simulations spanning more than 100 Mpc. These prescriptions yield distinct ionisation topologies and 21-cm statistical signatures even for similar global reionisation histories. The results motivate combining hydrodynamically informed source prescriptions with large-volume radiative transfer modelling to interpret forthcoming 21-cm observations; they are simulation findings, not observed reionisation signatures.
PublicThe researchers simulated how galaxies supplied light that ionised gas in the early universe. Their models were calibrated using JWST observations of distant galaxies and observational limits on how much ionising light escapes galaxies. Allowing star formation to vary unpredictably gave smaller dark matter haloes a larger share of the ionising output, creating a more fragmented pattern of ionised gas and slowing the growth of the largest ionised regions. Yet when models produced the same total number of ionising photons, their overall neutral-gas fractions and predicted 21-cm power spectra were almost identical. In a separate comparison, galaxy prescriptions drawn from three detailed simulations produced different ionised patterns and 21-cm statistics despite similar overall reionisation histories. These simulated differences could help interpret future observations.
Young explorerLong ago, light from galaxies changed gas in space. Scientists used computer models to explore how this happened. When the model galaxies made stars in a less steady way, the changed gas formed a more broken-up pattern. But some big-picture predictions stayed almost the same. Other ways of modelling galaxies made clearer differences. These are computer predictions, not things scientists have seen happen directly.
Yufei Zhen, Chun-Hao To, Boyan Yin+7 more
AstronomerUsing Cardinal-simulated LSST Year 4 and Roman HLIS photometry, the authors assess how incomplete spectroscopic coverage biases source-redshift calibration and weak-lensing cosmological inference. In these simulations, standard SOMPZ yields substantial overlap between tomographic bins and biased source-redshift distributions. Their Roman-SOMPZ pipeline uses individual-galaxy photo-z estimators as redshift references for binning and distribution estimation, including the new UMAP-flow-z estimator, which uses a UMAP embedding of deep-field colors to infer redshifts for galaxy phenotypes without spectroscopic representation. Relative to standard SOMPZ, it improves bin separation and reduces absolute mean-redshift biases in eight of nine bins. Propagating the estimated distributions into cosmological inference suggests that existing spectroscopy is adequate for early-stage Roman deep-field weak-lensing analyses, but full medium-tier cosmology requires further improvements in redshift characterization. These conclusions come from simulations, not Roman observations.
PublicWeak gravitational lensing uses small distortions in galaxy images to study the universe, but it requires reliable estimates of how galaxies are distributed in redshift, a measure related to distance. Galaxies with spectroscopic redshifts do not cover the full range of galaxies expected in Roman's High Latitude Imaging Survey, so calibration methods must fill in gaps. Using simulated LSST and Roman measurements, the researchers found that a standard method produced overlapping redshift groups and biased estimates. They developed Roman-SOMPZ, including a new estimator that uses galaxy colors to infer redshifts for types of galaxies missing from the spectroscopic sample. In the simulations, the new pipeline separated the groups better and reduced the average-redshift error in eight of nine groups. The analysis suggests that existing spectroscopy can support early Roman deep-field lensing studies, but the full medium-tier cosmology analysis will need better redshift characterization.
Young explorerScientists want to learn about the universe by looking at tiny changes in the shapes of faraway galaxies. They also need to know how far away those galaxies are, but some kinds are missing from their best distance checks. Using pretend galaxy pictures made by a computer, the researchers tested a new way to use galaxy colors to help fill those gaps. It sorted galaxies into distance groups better and made the average distance estimate closer to the right answer in eight of nine groups. The computer tests suggest that the checks scientists already have could be enough for some early Roman telescope studies, but more demanding studies will need better distance estimates.
Leah Jenks
AstronomerThe study predicts complementary signatures of primordial black holes formed by the collapse of early-universe curvature perturbations: gravitational waves sourced by those same perturbations and changes to the global 21 cm signal caused by PBH evaporation during the cosmic dark ages. For PBH masses of approximately 5 × 10^13–10^17 g, the predicted correlated signatures span gravitational-wave frequencies of roughly 10^-3–20 Hz, covering LISA, deci-Hz, and ground-based regimes, and 21 cm redshifts of about 300–30. The authors argue that these independent observational channels are within reach of near-future experiments and could jointly probe primordial physics. No detection is reported.
PublicThe study predicts two linked clues that could reveal black holes formed in the early universe. The disturbances that produced these primordial black holes would also generate gravitational waves, while evaporation of the black holes would alter the universe’s average 21-centimetre radio signal during its early dark ages. For a particular range of black-hole masses, the authors argue that both clues could be accessible to near-future experiments. Measuring them together would offer two independent ways to investigate the same early-universe physics, but the abstract reports a prediction, not an observation.
Young explorerScientists think tiny black holes might have formed when the universe was very young. The disturbances that made them could also have made ripples in space. As the black holes slowly lost energy, they could have changed an ancient radio signal too. This study says future experiments might find both clues and help us learn about the young universe. It does not say the clues have been found.
D. Anbajagane, C. To, M. Gaido+44 more
AstronomerThe authors construct a publicly available redMaPPer catalog of over 40,000 galaxy clusters from 13,000 square degrees of DECam griz imaging, spanning 0.2 < z < 0.9 and M_200c ≳ 10^14 solar masses/h. Photometric-redshift precision is σ_z/(1 + z) ≤ 0.008 below z = 0.65 and ≤ 0.011 at 0.65 < z < 0.9, with an outlier rate below 0.2%. Spectroscopy calibrates the cluster finding, but enlarging the spectroscopic sample does not improve cluster-redshift estimation. Cross-matches to millimeter-wave and X-ray catalogs yield observable scaling relations consistent across survey subsets and with prior catalogs and simulations. Joint millimeter-wave and optical analysis provides individual halo-mass estimates; measured lensing profiles from overlapping galaxy-shape catalogs are released to support further mass calibration. Tests find no appreciable impact of spatially varying imaging quality on catalog properties. A tested cylindrical richness observable is significantly simpler to model and achieves precision competitive with traditional optical richness.
PublicResearchers have assembled a catalog of more than 40,000 galaxy clusters using Dark Energy Camera images covering 13,000 square degrees of sky. They estimate cluster redshifts from images in four color bands, reporting high precision and fewer than 0.2% outliers. Spectroscopic data help calibrate the cluster search, although adding more such data did not improve the redshift estimates. By matching clusters with millimeter-wave and X-ray catalogs, the team measures relationships among cluster properties and finds agreement across different parts of the survey, with earlier catalogs, and with simulations. Combining optical and millimeter-wave data also gives estimates of individual cluster masses. The team releases measurements of gravitational lensing to help others refine mass estimates. Their tests find that variations in image quality across the sky do not appreciably affect the catalog's properties. They also test a simpler-to-model measure of cluster richness, finding precision competitive with the traditional measure. All data products and measurements are public.
Young explorerGalaxies are huge groups of stars, and many galaxies gather into even bigger groups called clusters. Scientists used pictures of a big part of the sky to make a list of more than 40,000 clusters. The colors in the pictures helped them estimate how far away the clusters are. They also used other kinds of light to help estimate how much stuff each cluster holds. Their checks suggest that differences in picture quality did not make much difference to the list. They shared their list and measurements so other scientists can study these giant galaxy groups too.
Radhika Achikanath Chirakkara, Christoph Federrath
AstronomerThree-dimensional hybrid particle-in-cell simulations determine the onset threshold for a turbulent dynamo in supersonic, weakly collisional plasma. For solenoidally driven turbulence at sonic Mach number approximately 2, the study varies Rm from approximately 31 to 1000 and tests initial Larmor-radius-to-box-size ratios of 1 and 100. Magnetic energy grows exponentially at sufficiently high Rm and decays at low Rm where magnetic diffusion dominates. Fits to the magnetic-energy growth rates yield Rm_crit = 190 (+21/-17) for the initially magnetised case and 198 (+16/-18) for the initially unmagnetised case. Their agreement within uncertainties indicates no significant dependence on initial magnetisation for the conditions tested. These simulation-derived thresholds exceed previously reported subsonic weakly collisional values, indicating that greater compressibility makes dynamo onset more difficult, and are approximately 1.5 times the reported threshold for supersonic MHD turbulence.
PublicTurbulent motion can strengthen magnetic fields in plasmas such as the solar wind and the gas within galaxy clusters, but only if that strengthening overcomes magnetic diffusion. This study uses three-dimensional computer simulations, rather than observations, to find the threshold in a plasma whose particles collide infrequently and whose turbulent motions are about twice the sound speed. Magnetic energy grows exponentially above a sufficiently high magnetic Reynolds number, a measure of the competition between motion and magnetic diffusion. The estimated thresholds are 190 (+21/-17) and 198 (+16/-18) for two different starting levels of magnetisation. These agree within their uncertainties, suggesting that the starting magnetisation does not significantly change the threshold under the simulated conditions. The thresholds are higher than earlier results for slower, subsonic turbulence in weakly collisional plasma and about 1.5 times the reported threshold for supersonic turbulence in a collisional plasma model. The comparison indicates that greater compressibility makes magnetic-field amplification harder to start.
Young explorerScientists used a computer to study a very hot gas with tiny particles that rarely bump into each other. They made the gas swirl faster than sound to see when its magnetic field could grow stronger. In the computer experiments, the field grew when the swirling could beat the process that weakens it. Two different starting magnetic fields needed about the same balance for growth, though the answers are not exact. Compared with earlier computer studies of slower swirling, making the field grow was harder.
Harry Desmond, Pedro G. Ferreira
AstronomerCurrent expansion measurements allow evolving dark energy with an equation of state apparently violating the null energy condition. One proposed explanation couples dark energy to dark matter, producing an equivalence-principle-violating fifth force acting only on dark matter. The authors predict that offsets between halo and stellar-disk centres would generate cup-shaped disk warps. Measuring 4,000 edge-on disks in Sloan Digital Sky Survey images and modelling both the fifth-force signal and competing baryonic effects, they find no predicted correlation between warps and the fifth-force field. For force ranges of at least 8 Mpc, they constrain the force strength relative to gravity to below 7.7 × 10^-4 at 95% credibility, weakening to 1.7 × 10^-3 with systematic uncertainties included. For an infinite-range scalar rolling today, even the conservative bound is three times stronger than the tightest cosmological bound, without depending on the scalar's cosmological evolution, and about two orders of magnitude below other astrophysical bounds. The result disfavours couplings preferred by recent interacting-dark-energy fits at 2–3 sigma unless gravitational screening is invoked.
PublicCould dark energy interact with dark matter through an extra force? This is one possible explanation for expansion measurements that allow dark energy to change over time, rather than remain a cosmological constant. The proposed force would act only on dark matter, shifting a galaxy's dark matter halo relative to its stars and bending its stellar disk into a cup shape. Researchers examined 4,000 galaxies viewed edge-on in Sloan Digital Sky Survey images, accounting for ordinary-matter effects that could also bend the disks. They found no expected link between the bending and the proposed force. For forces reaching at least 8 megaparsecs, the limit including systematic uncertainties is 0.17% of gravity's strength at 95% credibility. This challenges interaction strengths favoured by recent cosmological fits, but does not rule out every such model: gravitational screening could hide the force's effects.
Young explorerSome scientists think dark energy might give dark matter a special extra pull. If that happens, a galaxy's stars might bend into a cup shape. Researchers looked at pictures of 4,000 galaxies and did not find the bending pattern they expected from that pull. This helps them say how weak the pull would have to be, but it does not mean every version of the idea is wrong.
Arnab Mishra, Kanan K. Datta, Iffat Nasreen+2 more
AstronomerThis simulation study tests matched-filter detection of individual ionized bubbles around luminous sources in mock SKA-Low AA* HI 21-cm observations. The simulations include foregrounds, time- and frequency-correlated residual antenna gain errors, and system noise for 100 h of observing time. After foreground subtraction, matched filtering of the residual visibilities detects the simulated bubble and constrains its properties with residual gain errors up to approximately 1% rms in amplitude and 1 degree rms in phase. Comparable errors prevent reliable bubble identification in reconstructed images and bias the estimated HI 21-cm power spectrum. Longer temporal gain-error correlations increase image artifacts, whereas longer frequency correlations reduce them because foreground subtraction removes some spectrally smooth gain-induced residuals. Inferred bubble and IGM parameters remain largely unaffected, although their uncertainties can grow. These simulated results support the robustness of matched filtering under the tested calibration errors, rather than establishing an observational detection.
PublicDuring cosmic reionization, luminous sources created bubbles of ionized gas in the gas between galaxies. This study uses simulated radio observations to test whether such bubbles could be found despite leftover errors in telescope calibration. The mock SKA-Low observations represent 100 hours of observing and include the hydrogen 21-centimeter signal, foreground emission, calibration errors, and noise. After removing foreground emission, a method that searches for a bubble-shaped signal successfully detects the simulated bubble with calibration errors of about 1% in amplitude and 1 degree in phase. Similar errors make the bubble unreliable to identify in reconstructed images and distort a statistical measure of the hydrogen signal. Errors that remain correlated over longer times worsen image artifacts, while errors correlated across broader frequency ranges are partly removed with the foreground emission. The estimated bubble and surrounding-gas properties change little, though their uncertainty can increase. The findings demonstrate promise in simulations, not a detection in real observations.
Young explorerLong ago, bright things in space made bubbles where the gas around them changed. Scientists made pretend radio-telescope observations to see if they could find one of these bubbles even when the telescope's measurements had small mistakes. A special pattern-matching search found the pretend bubble, even when pictures made from the same measurements were too messy to spot it reliably. The search could also tell them about the bubble and nearby gas, although the mistakes sometimes made the answers less certain. This was a computer test, not a newly found bubble in the sky.
Chris Clarkson, Roy Maartens
AstronomerThis theoretical study calculates corrections to the local distance–redshift relation from velocity dispersion neglected in the dust approximation. Dispersion generates isotropic and anisotropic pressure whose gradients accelerate the mean matter flow, even while individual particles follow geodesics, introducing an intrinsic dipole. Using linear Vlasov perturbation theory about an FLRW background and a mean dispersion history motivated by halo estimates, the authors calculate this dipole and changes to expansion and shear. Pressure also alters structure growth and the spatial gradients controlling the redshift dependence of distance anisotropy. The largest correction at lowest order in redshift is to shear; expansion-gradient changes can yield a larger dipole at the next order. The predicted intrinsic dipole remains far below the observed low-redshift dipole, whose behaviour nearest the observer is dominated by relative motion between the matter and CMB frames. The assumed FLRW background precludes an independent test of the cosmological principle, and the numerical predictions depend on the adopted LCDM cosmology.
PublicAs cosmic structures form, matter particles develop a spread of velocities that is ignored when matter is treated as pressureless dust. This study calculates how the resulting pressure can change the average flow of matter and make the relationship between distance and redshift differ across the sky. In the calculation, pressure changes both the overall expansion and its directional differences, as well as how those differences vary with redshift. The predicted dipole—a pattern that differs between opposite directions—is much smaller than the dipole observed at low redshift. Closest to us, the observed pattern is dominated by motion between matter and the reference frame of the cosmic microwave background. These are theoretical predictions, not new measurements: their numerical size depends on the chosen cosmological model, and the assumed uniform, direction-independent background prevents an independent test of that assumption.
Young explorerSpace is full of moving matter. When big clumps form, their tiny pieces move at different speeds. Scientists used maths to work out how this could change the way matter moves together, making the link between a galaxy’s distance and its stretched light a little different in opposite directions. Their calculation predicts a much smaller difference than astronomers actually see nearby. Very close to us, that observed difference mostly comes from matter moving compared with the universe’s leftover light. The calculation depends on the picture of the universe the scientists chose; it is not a new measurement.
Paula S. Ferreira, Carlos A. P. Bengaly, Renyue Cen
AstronomerThe Cross-Tracer Clustering Ratio (CTCR) divides the early-type galaxy auto-power spectrum by the early–late-type cross-power spectrum. In the matched-kernel, deterministic linear-bias limit, the projected matter spectrum, including BAO wiggles, cancels, leaving relative linear bias; residual acoustic structure therefore probes departures from this limit through differential normalised nonlinear responses. The authors fit a smooth scale-dependent baseline multiplied by an acoustic template, jointly constraining its amplitude A_morph and the BAO dilation parameter alpha. Applied to nine DESI Legacy Survey DR8 bins over 0.1 < z < 0.9, the fit gives alpha = 0.9997 ± 0.0383, consistent with Planck 2018 ΛCDM, and A_morph = 0.369 ± 0.307, consistent with zero. Bayesian model comparison gives at most a 2.6-sigma preference for the acoustic template, so the differential acoustic response is not firmly established. The estimator requires no external absolute-bias calibration. Testing halo occupation and assembly-bias models and cross-checking spectroscopic BAO measurements are proposed applications.
PublicResearchers compared how early-type galaxies cluster with how they cluster alongside late-type galaxies. Their new ratio is designed so that, under specific simplifying assumptions, the usual cosmic acoustic pattern cancels out. Any remaining pattern could then reveal differences in how the two galaxy populations trace matter beyond that simple description. Using nine redshift groups from the DESI Legacy Survey, they measured an acoustic scale consistent with the Planck 2018 standard cosmological prediction. However, the strength of the difference between galaxy types was consistent with zero, and the evidence for a remaining acoustic pattern was not conclusive. The authors propose the method as another way to test galaxy-clustering models and check other cosmic acoustic measurements.
Young explorerGalaxies are huge groups of stars, and they come in different shapes. Scientists compared where two kinds gather, using a new trick meant to hide a pattern they share and look for a difference. They tried it with a galaxy survey, but they are not yet sure that a difference is really there. The trick could help them check ideas about how galaxies gather.
Madeline L. Cross-Parkin, Ignacio Magaña Hernandez, Antonella Palmese+2 more
AstronomerThe authors introduce a dark-siren inference framework that jointly estimates H0 and the mixing fraction of two galaxy host-weighting prescriptions. This addresses uncertainty in whether compact-binary merger rates trace properties such as stellar mass or star formation rate; the mixture components may represent distinct formation environments, but that interpretation is not established. Tests with simulated catalogues show that marginalising over the mixture uncertainty preserves unbiased H0 constraints while permitting inference of the populations’ relative contributions. An A#-like detector network with roughly 1,000 dark sirens may be able to exclude models in which hosts follow only one of the two prescriptions. These are simulation-based findings and forecasts, not measurements from an observed dark-siren sample.
PublicGravitational-wave signals from merging compact objects can be combined with galaxy catalogues to estimate how fast the Universe is expanding, even when the host galaxy is not identified. A key uncertainty is how to rank the possible hosts: mergers might favour galaxies according to their stellar mass, their rate of forming stars, or a mixture of patterns. The researchers propose fitting a mixture of two host-selection rules alongside the expansion rate. In simulated catalogues, accounting for this uncertainty avoids bias in the inferred expansion rate and lets the signals constrain the mixture. They forecast that an A#-like detector network collecting about 1,000 such signals might rule out explanations based entirely on either rule. The method could also offer clues about where merging binaries form, but it has not established those formation environments.
Young explorerWhen two very small, heavy objects in space come together, they send out ripples. Scientists can use those ripples and a list of galaxies to work out how fast the Universe is growing, even if they do not know which galaxy the ripples came from. But they need a fair way to guess which galaxies are more likely homes. The researchers tried mixing two guessing rules in pretend sets of galaxies and signals. Their tests gave answers that were not pushed too high or too low, and helped them work out how much of each rule was needed. This is a promising test with made-up data, not yet a result from real signals.
Sean Patrick MacBride, Isaac McMahon, Danny Laghi+8 more
AstronomerUsing DELVE DR3 and the fifth Gravitational-Wave Transient Catalog, the authors measure H0 by statistically associating gravitational-wave localizations without electromagnetic counterparts with potential host galaxies. Adapting the dark siren analysis to DELVE’s photometrically heterogeneous footprint requires magnitude cuts of 15.5 < m_r < 20 to exclude saturated sources and control known photometric-redshift bias, an evolving luminosity function, and regional de-biasing based on survey depth and photometric-redshift precision. They obtain H0 = 67.4 (+13.0, −11.2) km s⁻¹ Mpc⁻¹ from dark sirens alone and 70.6 (+8.7, −7.0) km s⁻¹ Mpc⁻¹ after combining with the bright siren GW170817. Tested photometric-band and luminosity-function choices have subdominant effects on the posterior. The results demonstrate feasibility for wider-area, non-uniform catalogs and additional constraining power relative to the spectral siren method. Analyses using forthcoming LSST, Euclid, and Roman catalogs remain a future opportunity.
PublicThe study uses gravitational waves to estimate how fast the Universe is expanding. For events without an accompanying light signal, researchers statistically compare their possible locations with a galaxy catalog rather than identify a single host galaxy. Using DELVE survey data, they estimate an expansion rate of 67.4 (+13.0, −11.2) kilometers per second per megaparsec. Adding the event GW170817, which had an accompanying light signal, gives 70.6 (+8.7, −7.0) in the same units. The analysis required adjustments for uneven survey quality and biases in galaxy distance estimates. These measurements provide input to the disagreement between early- and late-Universe expansion estimates, but their uncertainties remain substantial. The work supports using larger, uneven galaxy surveys for future measurements.
Young explorerSpace is stretching, and scientists want to know how fast. They studied tiny ripples in space and compared where they might have come from with a list of galaxies. They had to be careful because some parts of the list were clearer than others. Adding one ripple event that also had a light signal helped narrow their estimate, but there is still plenty of uncertainty.
Bryan Cordero-Patino, Álvaro Duenas-Vidal, Jorge Segovia
AstronomerMotivated by JWST observations of unexpectedly massive galaxies at high redshift, the authors develop an axion cold-dark-matter model with a non-minimal coupling to gravity. They evaluate gravitational instability in the hydrodynamic limit and find that it depends on the non-minimal coupling parameter. They propose this framework as a tool for addressing the high-redshift observations, but the abstract reports no quantitative comparison with the data or demonstrated resolution of the discrepancy.
PublicObservations by the James Webb Space Telescope have revealed unexpectedly massive galaxies in the early universe. Motivated by these findings, the researchers develop a theoretical model in which axions make up cold dark matter and interact with gravity through an additional coupling. Their calculations show that gravitational instability—the tendency for matter to clump under gravity—depends on the strength of this coupling. The model could help researchers address the telescope’s findings, but the abstract does not establish that it explains the observed galaxies.
Young explorerA space telescope has spotted galaxies from long ago that seem surprisingly massive. Scientists made a math model of dark matter, a kind of matter we cannot see directly, with a different way of connecting to gravity. In their model, changing that connection changes how matter starts to gather into clumps. This might help explain those galaxies, but they have not shown here that it does.
Jian Hu, Yi Liu, Jian Ping Hu+1 more
AstronomerThis late-time, model-independent distance-consistency analysis combines strong gravitational lenses, ultraviolet/X-ray quasars, and 38 Sunyaev–Zel’dovich/X-ray cluster angular-diameter distances, emphasizing systematics rather than competitive curvature constraints. Excluding 30 of 158 lenses that fail the isothermal-reference geometric requirement leaves 128 systems; deterministic one-to-one matching to 1598 quasars produces 100 pairs at a nominal 5% distance-mismatch threshold. Including measured X-ray flux uncertainties, intrinsic quasar scatter, and the full covariance from shared quasar distances in the smoothed cluster predictions gives Ω_K = 2.085 (+1.634, −1.103) at 68%, with a central 95% interval of [0.269, 6.028], under a uniform prior on [−10, 10]. The authors explicitly attribute the positive offset to cross-probe calibration tensions, sample assignment, and the cluster anchor, not intrinsic spatial curvature or evidence for an open Universe. Lenses plus quasars alone leave curvature essentially prior dominated; omitting only the off-diagonal cluster covariance shifts the posterior to Ω_K = 5.21 (+2.46, −2.07). The cluster anchor therefore supplies most of the constraining power, and its covariance substantially affects the inferred location.
PublicThe researchers compared cosmic distances inferred from gravitational lenses, quasars, and 38 galaxy clusters to examine how analysis choices affect estimates of the Universe’s spatial curvature. After filtering and matching the data, they used 100 lens–quasar pairs and accounted for linked uncertainties caused by reusing the same quasar distances in the cluster comparison. Their combined analysis favored a positive curvature-parameter value, but they explicitly say this is not evidence for an open Universe: they attribute the shift to calibration tensions between the methods, sample matching, and the influence of the cluster distances. Without the clusters, the data barely constrain curvature within the allowed range. Ignoring correlations among the cluster comparisons also shifts the estimate substantially. The main finding is a warning about systematic effects, not a reliable measurement of cosmic curvature.
Young explorerThe researchers compared different ways of measuring distances in space to see what they might tell us about the shape of the Universe. Their answer changed a lot depending on how they combined the measurements and counted their uncertainties. They say the answer does not show that the Universe has a particular shape. Instead, it shows why these space-measuring methods need to be checked carefully.
Daniela Galárraga-Espinosa, Daisuke Nagai, Isabel Medlock+3 more
AstronomerUsing 5,637 filaments in the TNG300-1 simulation at z=0, the authors identify gaseous linear mass density, Λ = M_gas/L_fil measured within the radius of peak radial gas entropy, as an organising parameter analogous to halo mass. Across more than two decades in Λ, simulated filaments follow a continuous sequence from long, thin, cool, metal-poor structures to shorter, wider, hotter, more enriched ones. Core temperatures span two orders of magnitude across the warm–hot intergalactic medium range. Temperature weighting indicates that hotter gas preferentially occupies denser material at low Λ but diffuse material at high Λ. Scaling relations link Λ to temperature, electron density, pressure, entropy, and metallicity; the temperature relation is qualitatively consistent with gravitational heating. The authors report the first gaseous linear mass density function, measured in this simulation, with a flat low-Λ regime and steep exponential high-Λ decline. Integrated Compton-y scales systematically with Λ, motivating a thermal Sunyaev–Zel’dovich proxy for current surveys. Galaxy richness per unit length correlates with Λ at Pearson r=0.80, suggesting a spectroscopic classification route and guidance for missing-baryon searches. These are simulation findings and proposed observational applications, not observational detections.
PublicCosmic filaments are strands of gas connecting the large-scale cosmic web and are thought to contain much of the ordinary matter that remains difficult to locate nearby in the universe. In a computer simulation of 5,637 filaments, researchers found that the amount of gas per unit length provides a useful way to organise their properties. Filaments with more gas per unit length tend to be shorter, wider, hotter, and richer in elements heavier than helium. Their hottest gas also tends to be more spread out, rather than concentrated in denser regions. The simulated trends are qualitatively consistent with heating by gravity. The authors suggest that galaxy counts along filaments and a gas-related imprint on the cosmic microwave background could help identify and classify these structures in surveys. Those observational applications are proposed uses of the simulation results, not demonstrated detections of the missing matter.
Young explorerThe universe has a giant web, with gas along its threads. Scientists studied a computer-made version of this web. Threads with more gas packed into each bit of their length tended to be wider and hotter. Counting galaxies along real threads might help scientists find gas that is hard to see. The computer study suggests where to look; it has not found that hidden gas in the real sky.
André Z. Vitorelli, Eduardo S. Cypriano
AstronomerThe authors simultaneously fit individual cluster weak-lensing ΔΣ profiles, linking mass and concentration to richness, redshift and the BCG-to-brightest-satellite magnitude gap. They compare this joint fit with a forward-modelled stack using the same model and priors, and a standard two-step analysis. In mocks with triaxial haloes and miscentering at DES Y3-like and LSST-like source densities, all methods recover the injected concentration–gap slope with calibrated uncertainties. The joint fit has 1.2–1.3 times less scatter than the forward-modelled stack and 2–6.5 times less than the two-step method; the latter also biases several other scaling parameters. For WaZP clusters with DES Y3 shears, allowing mass at fixed richness to depend on gap yields γ_cm = 0.065 ± 0.033 mag⁻¹ for the forward-modelled stack and 0.007 (+0.032/−0.033) mag⁻¹ for the joint fit. Neither constitutes a detection. Both mass–concentration slopes are consistent with zero, as expected from the cited relation’s upturn over this mass range. Apparent concentration–gap coupling is therefore sensitive to the adopted model.
PublicCombining many galaxy clusters into an average can make weak gravitational-lensing measurements clearer, but loses information about individual clusters. This study instead fits all clusters together while retaining their individual measurements. In simulated data, the approach measured a link between cluster concentration and the brightness difference between the central galaxy and its brightest satellite more precisely than two averaging-based methods. In real DES data, however, the authors find no secure evidence for that link when their model also allows cluster mass to depend on the brightness difference. The results caution that an apparent connection between brightness differences and how concentrated clusters are can depend on the model used.
Young explorerScientists study groups of galaxies to learn how tightly packed they are. Instead of mixing all the groups into one average, they tried studying them together while keeping each group’s details. This worked better in make-believe groups used for testing. In real groups, they could not be sure that a bigger brightness difference between the main galaxy and its brightest companion meant the group was more tightly packed. The answer depended on the rules used to describe the groups.
Joshua Layton, Alex Hall, Naomi Clare Robertson
AstronomerThis reanalysis of DESI DR2 BAO, Planck 2018 CMB, and Type Ia supernova datasets (DES-SN5YR, DES-Dovekie, Pantheon+, Union3) examines the effect of replacing uniform priors with the Jeffreys prior in posterior inference and Bayesian evidence calculations. A fully JAX-based pipeline combines CosmoPower-JAX emulators, NUTS posterior sampling, and accelerated nested sampling. Constraints on w0 and wa remain largely robust, with only minor shifts of marginalised posteriors toward the maximum a posteriori in less constraining dataset combinations. Model selection is much more prior-sensitive: the Jeffreys prior reverses preferences for dynamical dark energy found under uniform priors and strengthens existing preferences for ΛCDM. The authors attribute this primarily to a larger Occam penalty against overfitting by w0waCDM. These are prior-dependent model-comparison results, not a prior-independent determination of dark-energy evolution.
PublicThe researchers reanalysed measurements of cosmic distances, the early universe, and exploding stars to compare models with constant or changing dark energy. They changed the statistical prior—the rule used to weight possible parameter values before incorporating the measurements—from uniform priors to the Jeffreys prior. Estimates of the parameters describing changing dark energy barely moved, but the models’ Bayesian rankings changed substantially. Data combinations that favoured changing dark energy with uniform priors instead favoured the constant-dark-energy model with the Jeffreys prior; existing preferences for that simpler model also strengthened. The authors attribute this mainly to a stronger penalty for the changing model’s ability to overfit the data. The study shows that these model rankings depend strongly on the prior, rather than establishing whether dark energy actually changes.
Young explorerScientists used space measurements to compare two ideas: dark energy stays the same, or it changes. They changed a rule for weighing the possible answers. Their estimates hardly changed, but which idea scored best did change, favouring the stay-the-same idea. That does not prove dark energy stays the same.
Joey Braspenning, Annalisa Pillepich, Marine Prunier+2 more
AstronomerThis ERGO-ML study presents a simulation-based inference method for recovering the multiphase temperature distribution of the intracluster medium from X-ray spectra. A neural network is trained on synthetic 0.1–10 keV spectra for approximately 100,000 sightlines through TNG-Cluster systems with M200c = 10^14.2–10^15.2 solar masses. In simulation-based tests using XRISM-like and Chandra-like spectral resolutions and realistic photon noise, the method recovers mass-weighted temperatures for individual sightlines and whole clusters with an average prediction error below 0.01 dex, and total gas mass within 0.04 dex. It also estimates sub- and super-virial gas fractions, extracts a cooler phase whose flux contribution is 1,000 times lower than that of the virial phase, and recovers multiphase gas spatial distributions in relaxed and merging systems. These results establish performance on simulated spectra, not validation on observed clusters, and motivate future studies of feedback, accretion and merging.
PublicThe hot gas inside galaxy clusters contains regions at different temperatures, but separating those components using X-ray observations is difficult. The researchers trained a neural network on artificial X-ray spectra generated from a cosmological simulation, then tested its ability to infer the gas’s temperature distribution and mass. With spectral detail resembling XRISM and Chandra and realistic photon noise, the method recovered average temperatures and total gas masses accurately in the simulated cases. It also identified cooler gas even when its X-ray contribution was 1,000 times fainter than the main gas component, and reconstructed where gas at different temperatures lay in both settled and merging clusters. The abstract reports tests on simulated data rather than real cluster observations. The approach could help researchers study how energy input, incoming material and mergers affect cluster gas.
Young explorerA galaxy cluster is a big group of galaxies with very hot gas between them. Some of that gas is cooler or hotter than the rest, and telling the parts apart is hard. Scientists taught a computer using pretend X-ray light made in a simulation. In those tests, the computer could work out how hot the gas was and find cooler gas even when its light was much fainter. It could also tell where different-temperature gas was. These tests used simulated clusters, not real observations yet.
Mayeul Aubin, Florent Leclercq, Guilhem Lavaux
AstronomerThe authors present a computational framework for survey-scale dark matter lightcone mocks using spatial COmoving Lagrangian Acceleration (sCOLA). Independently evolved tiles are simulated only where they intersect the region of interest and stopped once the observer’s past lightcone has left them. An LPT buffer approximates particle inflow, while a second-order perturbative boundary potential improves large-scale accuracy and permits smaller tiles and buffers. In a comparison with Gadget4 in a 3.84 h^-1 Gpc box containing 3840^3 particles, the lightcone reproduces the matter power spectrum to 1%, velocity-divergence power spectrum to 1.5%, and equilateral bispectrum to 2% up to k approximately 0.4 h Mpc^-1, with no visible tile-boundary discontinuities. These are simulation-validation results, not observational measurements. The tested run used 1300 CPU hours, 2600 times less than the reference run. Exploiting independent-tile parallelism, the authors estimate that 10^7 CPU hours could produce approximately 25,000 Euclid Galactic north-cap realisations at a mass resolution of 10^11 solar masses; this ensemble is a projected capability, not a reported production result.
PublicGalaxy surveys need many simulated universes to help interpret their measurements, but detailed simulations are expensive. This work presents a faster way to simulate the dark matter within the portion of space and cosmic history a survey would see. It divides the calculation into independently evolving patches, skips irrelevant patches, and stops each calculation when it is no longer needed. Improved treatments of patch boundaries help the pieces fit together accurately. Compared with a more expensive reference simulation, the method matched three measures of structure and motion within 1–2% over the tested range of scales, with no visible seams between patches. The demonstration used 1300 CPU hours, 2600 times less than the reference calculation. The authors project that this efficiency could enable thousands of survey-sized simulations; they do not report having produced that full collection.
Young explorerScientists make pretend universes on computers to help understand maps of galaxies. This team made a faster way to do that: split the pretend universe into little pieces and work only on the pieces needed for the map. Their test looked very close to a slower computer version, though it was not exactly the same. They think this could help them make thousands of pretend maps.
Hernán E. Noriega, Josue De-Santiago, Gabriela Garcia-Arroyo+2 more
AstronomerThis updated analysis constrains non-standard neutrino self-interactions described by an effective heavy mediator, using DESI DR1 full-shape clustering, BAO, Lyman-alpha 1D power spectra, and CMB data. Multimodality in the profile likelihood motivates separate moderately interacting (MIν) and strongly interacting (SIν) regimes. DESI FS+BAO disfavors SIν, slightly more strongly when Lyman-alpha is included. With Lyman-alpha, the MIν region is bimodal: a sharp intermediate mode near G_eff ≈ 10^-3 MeV^-2 is not penalized relative to the weaker, standard-like mode. The combined Planck, ACT, and SPT likelihood (CMB-SPA) disfavors SIν more strongly than Planck alone. FS+BAO+CMB-SPA gives the strongest evidence against SIν reported in this analysis, with odds of 5:100000. These are model constraints, not a detection of non-standard interactions.
PublicResearchers tested whether neutrinos could interact with one another through a proposed heavy particle, using measurements of galaxy clustering, cosmic distances, hydrogen absorption, and the cosmic microwave background. The data disfavor the strongly interacting version of this model. Combining DESI galaxy-clustering and distance measurements with microwave-background data from Planck, ACT, and SPT gives the strongest evidence against that version reported in the study, with odds of 5 to 100,000. The conclusion is less decisive for more moderate interactions: when hydrogen-absorption measurements are included, one narrow range of interaction strength is not penalized compared with a weaker, standard-like alternative. That does not establish that these extra interactions exist.
Young explorerNeutrinos are tiny particles. Scientists used measurements of space to check an idea: could neutrinos interact with each other in an extra way? A version where they interact strongly did not fit the measurements well. A gentler version still fits about as well as one with much weaker interactions, but that does not mean scientists have found this extra interaction.
Matteo Braglia, Gabriele Franciolini, Nadir Ijaz+1 more
AstronomerThis semi-analytic study examines scalar backreaction in single-field inflation models with transient ultra-slow-roll (USR) or an oscillatory feature (OF), using a mean-field treatment in the decoupling limit. The treatment can reproduce recent lattice results, but identifies spurious sensitivity to ultraviolet Bunch–Davies vacuum contributions unless these are removed by adiabatic subtraction. In the OF model, copious particle production separates amplified physical modes from the ultraviolet vacuum tail, reducing this sensitivity and making lattice results more reliable in that regime. For USR, adiabatically subtracted spectra imply milder backreaction on the background evolution than previously inferred. These are theoretical findings within the stated approximation, not observational results.
PublicThe study explores whether small-scale fluctuations can significantly alter the overall expansion in certain models of inflation, an early period of cosmic expansion. Using approximate theoretical calculations and comparisons with previous computer simulations, the researchers find that vacuum contributions at very short wavelengths can distort estimates of this feedback unless a mathematical subtraction procedure is applied. In a model with a temporary ultra-slow-roll stage, the corrected calculations indicate weaker feedback than previously inferred. In a model with an oscillating feature, abundant particle production makes the amplified physical fluctuations easier to separate from the vacuum contribution, making simulations more reliable in that regime. The conclusions concern theoretical models, not measurements of the universe.
Young explorerScientists used math to study how tiny wiggles might change the way the very early universe grew. Their calculations suggest that some wiggles from empty space can make the effect look too big unless they are carefully subtracted. In one kind of model, this subtraction makes the effect smaller than earlier work suggested. In another kind, lots of particles help make the important wiggles easier to pick out. This is a study of models, not something scientists watched happen.
Jun-Xian Li, Shuang Wang, Liang-Gui Zhu
AstronomerThis forecasting study tests how the fiducial cosmology used to generate mock TianQin bright standard sirens from massive black hole binary mergers affects dark energy inference. Catalogs generated under ΛCDM (TQSS1) and a redshift-binned dark energy reconstruction model (TQSS2) differ by at most 1.48% in their distance–redshift relations. Analyzed within the Chevallier–Polarski–Linder model, either mock catalog alone yields constraints similar to those from supernova data. Combined with DESI DR2 BAO, Planck 2018 CMB, and DESY5 supernova data, TQSS1 and TQSS2 are forecast to favor dynamical dark energy at 2.3σ and 3.8σ, respectively. These are forecast preferences, not TianQin detections. The different massive black hole seed models considered do not alter the cosmological implications. The results highlight that small differences between mock catalogs can accompany appreciable differences in forecast dark energy preferences, motivating forecasts with multiple fiducial cosmologies.
PublicResearchers simulated how future gravitational-wave measurements by TianQin could help study dark energy and the expansion of the universe. They created two catalogs of signals from merging massive black holes, assuming either the standard ΛCDM cosmology or an alternative model that allows dark energy to vary across cosmic history. The simulated distance–redshift relations differed by no more than 1.48%, and either catalog alone provided cosmological constraints similar to those from supernova observations. Yet when combined with existing galaxy-clustering, cosmic microwave background, and supernova data, the two catalogs gave different forecast preferences for changing dark energy: 2.3σ versus 3.8σ. These are simulation-based expectations, not evidence from actual TianQin measurements. The black hole seed models tested did not change the cosmological implications. The study shows why assumptions used to build simulated data matter when predicting what future observations might reveal.
Young explorerScientists made two sets of pretend signals from giant black holes joining together. They wanted to see how a future space detector called TianQin might help us learn how the universe grows. The two sets used different ideas about dark energy, something scientists study to understand why the universe’s growth is speeding up. The pretend signals looked very similar, but when mixed with real sky information, they gave different strengths of clues that dark energy might change over time. This does not mean TianQin has found changing dark energy. It shows that the ideas scientists put into a pretend test can affect what they expect to learn.
Tomotaka Kuroda, Fumiya Sano, Yusuke Yamada
AstronomerThis theoretical Letter summarizes the Cosmological Classical Branches (CCB) framework for connecting a superposed primordial quantum state to the single classical realization of curvature perturbations assumed in standard cosmology. It argues that squeezing and decoherence alone do not establish the physical meaning of that description. CCBs instead use physical records: distinct late-time matter components encode compatible records of the same primordial configuration. One record makes the configuration readable, while a disjoint compatible record suppresses interference accessible to operations on the first component. Each branch thereby supports a common classical, c-number primordial label at finite resolution without eliminating the global quantum superposition. The abstract presents a conceptual framework, not an observational demonstration.
PublicCosmologists describe the universe’s early fluctuations using quantum physics, which allows a superposition of different configurations. Yet calculations of the universe’s later history assume one definite configuration. This theoretical paper summarizes a proposed way to connect those descriptions, called Cosmological Classical Branches. In this framework, different components of matter retain matching physical records of the same early configuration. Those records make the configuration readable and suppress quantum interference accessible through operations on one component. A branch can then be described by a shared classical label, with limited precision, even though the overall quantum superposition remains. The abstract does not report observational evidence establishing this framework.
Young explorerScientists use quantum rules to describe the very young universe, but they describe its later story as one definite story. This paper explains an idea for joining those pictures. Different parts of the universe could hold matching clues about how it began. Those clues could let each branch of the quantum picture be described like one ordinary story, without erasing the whole quantum picture. This is an idea scientists are developing, not something this paper says they have seen happen.
Mariaveronica De Angelis, Javier Rubio
AstronomerThis theoretical study addresses the tension between high-scale inflation and QCD axion dark matter produced by pre-inflationary misalignment under CMB isocurvature bounds. In a broad class of scale-invariant models, a dynamical field ratio sets the axion kinetic normalisation without dimensionful parameters in the classical action. The field-space metric today controls the abundance, while its value at horizon crossing controls primordial fluctuations. A sufficiently large inflationary metric suppresses isocurvature, permitting the classic axion window with untuned misalignment and sub-Planckian decay constants. Exact scale and Peccei-Quinn symmetries enforce a non-turning inflationary attractor, conserving super-Hubble curvature perturbations and preserving the single-field adiabatic spectrum. An explicit Higgs-Dilaton realisation deforms the Peccei-Quinn kinetic term and produces an alpha-attractor inflaton sector near the Starobinsky point. Importantly, this particular realisation has a super-Planckian present decay constant: it instead reopens the anthropic window at high inflationary scales, with an ultralight QCD axion subject to black-hole superradiance constraints. These are model results, not an axion detection.
PublicAxions are proposed particles that could make up dark matter. However, measurements of the cosmic microwave background strongly restrict a standard axion scenario when combined with inflation at high energy scales. This theoretical paper proposes a way to ease that conflict: let a changing field-dependent factor govern the axion differently during inflation and today. It could suppress early axion fluctuations without fixing today's dark matter abundance in the usual linked way. The general mechanism allows high-scale inflation in the classic axion window without a finely adjusted initial angle. The authors also construct a specific example, but it occupies a different parameter range, called the anthropic window, and contains an ultralight axion constrained by black-hole physics. The work presents theoretical possibilities, not evidence that axions have been found.
Young explorerScientists wonder whether tiny particles called axions could be the invisible matter in space. But one idea about them is hard to fit with clues from light left over from the early universe. This paper uses maths to show how changing the rules for axions as the universe grows might help the ideas fit together. It does not show that axions have been found.
Shuntaro Aoki, Masahide Yamaguchi
AstronomerThis theoretical note introduces the Hubble susceptibility of cosmological-collider masses, encoded in the scale dependence of squeezed-limit oscillations. Heavy fields generically acquire Hubble-induced mass corrections during inflation. The authors show that the local oscillation frequency and its drift can separate these corrections from an intrinsic mass contribution at leading slow-roll and adiabatic order. This is a theoretical result, not a reported observational measurement.
PublicDuring inflation, heavy fields can receive changes to their masses because of the universe’s expansion. This theoretical study introduces a way to describe that sensitivity using how an oscillating pattern changes with scale. The authors show that the pattern’s frequency and the way that frequency shifts could distinguish the expansion-related mass change from an intrinsic mass contribution. The result uses leading-order approximations and is not an observational detection.
Young explorerImagine a wiggly pattern that could give clues about the universe when it was very young. Scientists worked out how the wiggles might help tell apart two parts of something’s mass: a part of its own and a change caused by the universe growing. This is a math idea with simplifying assumptions, not something they have seen.
Digvijay Wadekar, Barak Zackay, Mark Ho-Yeuk Cheung+7 more
AstronomerThe authors present a two-image lensing search method that constructs matched-filter outputs from the SNR time series already computed with unlensed templates. Its marginalized detection statistic requires no additional matched filtering and is reported to be more than 150 times faster than an explicit lensed template bank. For overlapping images in the geometric-optics regime, it recovers at least approximately 97% of optimal SNR for point-mass and singular isothermal lenses, whereas unlensed templates can recover as little as 67%; substantial gains are also reported for Chang-Refsdal and cored isothermal lenses. The method also restores signal consistency for overlapping lensed signals otherwise down-ranked as noise transients, increasing sensitive volume roughly two- to fourfold for those strongly down-ranked signals. For separated images, it enables coherent searches for pairs with neither image individually significant. Near fold caustics, reported sensitive-volume gains are factors of 1.8–2.6 over requiring two independent detections and up to 1.6 over a targeted counterpart search. These are method-performance results, not reported astrophysical detections. The construction applies to any matched-filtering search.
PublicGravity can split the signal from a merging pair of objects into two copies that either overlap or arrive separately. The authors describe a faster way to search for these lensed signals by reusing calculations that existing searches already perform. They report that it is more than 150 times faster than explicitly searching a bank of lensed signal patterns. For several lens models, it captures signal strength that ordinary searches miss and helps prevent overlapping copies from being rejected as noise. It can also combine two separated copies even when neither is convincing alone. The reported improvements depend on the lens and signal configuration; they demonstrate a search method’s performance, rather than announce a detected lensed merger.
Young explorerWhen two objects in space join together, their signal can reach us along two paths because gravity bends its way. The two copies might arrive together or one after the other. Scientists describe a quicker way to look for both copies using work their searches already do. Their tests show it can help find signals that other searches might miss, but they are not announcing a new discovery in space.
Itzi Aldecoa-Tamayo
AstronomerThis thesis studies primordial black hole (PBH) evolution in Randall–Sundrum Type II braneworld cosmology, including a preliminary discussion of early gravitational collapse in the small-black-hole limit. A fully relativistic accretion analysis combines Michel theory with the covariant Shiromizu–Maeda–Sasaki formalism. Within this model, higher-dimensional effects enhance early accretion onto light PBHs: discrepancies from previous mass estimates grow as t^0.33 and reach several orders of magnitude by the end of strong accretion, changing the inferred mapping from initial masses to present-day populations. A second study reanalyses Hawking-radiation, diffuse gamma-ray, microlensing, and cosmic microwave background energy-injection constraints using higher-dimensional evaporation dynamics and updated surveys. The combined analysis identifies parameter regions allowing PBHs to constitute all dark matter while satisfying current bounds. Enhanced accretion also permits PBHs contributing significantly to dark matter to originate below the effective four-dimensional Planck mass. These are model-dependent theoretical and constraint-analysis results, not a detection of PBH dark matter.
PublicCould black holes formed in the early universe make up all dark matter? This thesis explores that possibility in a theory with an extra spatial dimension. Its calculations suggest that light primordial black holes would gather matter much more efficiently early on than previous estimates indicated, substantially changing how their birth masses relate to their masses today. The work also reassesses limits from radiation, gravitational lensing, and the cosmic microwave background, accounting for how black holes evaporate in this theory. Some combinations of model parameters remain compatible with current observations even if primordial black holes supply all dark matter. This establishes a theoretical possibility within the model, not evidence that such black holes actually explain dark matter.
Young explorerScientists wonder if black holes born when the universe was very young could be the hidden stuff called dark matter. This study uses a picture of the universe with an extra direction in space. In that picture, little black holes could grow faster than earlier guesses suggested. They might make up all the dark matter without breaking the rules set by what we see, but we do not know if they really do.
David Touzeau, Francis Bernardeau, Karim Benabed+1 more
AstronomerThe authors design a null test based on the Bernardeau–Nishimichi–Taruya (BNT) transform for tomographic cosmic shear and forecast its performance for Stage IV weak-lensing surveys. The transform nulls contributions from low-redshift lenses and depends on the cosmic expansion rate rather than matter-distribution properties, allowing background-evolution constraints even from nonlinear scales. Fisher-matrix analysis combined with parameter sampling indicates that the approach could significantly tighten constraints on the dark-energy equation of state. These are forecasts, not observational results. Apart from photometric-redshift uncertainties, performance is expected to be limited primarily by shape noise rather than cosmic variance, suggesting scope for improvement through future survey design.
PublicThis study proposes a way to learn about the Universe’s expansion from the subtle distortions of distant galaxies caused by intervening matter. A mathematical transformation removes the contribution from relatively nearby matter in a way that depends on cosmic expansion, without depending on the properties of matter’s distribution. Forecast calculations for next-generation surveys suggest that the method could substantially improve constraints on dark energy’s equation of state, which relates its pressure to its energy density. This improvement has not yet been demonstrated with observations. Uncertain galaxy-distance estimates remain important; otherwise, the forecasts suggest that noise from galaxy shapes would matter more than variation between surveyed regions of the Universe.
Young explorerMatter between us and faraway galaxies can make those galaxies look a little bent. Scientists propose a way to leave out the bending caused by nearby matter and learn how the Universe grows. Their calculations suggest it could help us understand dark energy better, but they have not shown this with real observations yet. Unclear galaxy shapes and uncertain distances could make the job harder.
Xiaoyun Shao, Facundo Toscano, Diego Garcia Lambas+5 more
AstronomerThe authors examine the CMB’s apparent approach to homogeneity at smaller angular scales than expected in standard ΛCDM, using the homogeneity scale H and the slope of the homogeneity index at θ = 90°. Removing low multipoles, particularly the quadrupole, from both observations and synthetic ΛCDM maps significantly improves their consistency. Masking regions affected by an extragalactic foreground, especially those associated with local galaxies expected to influence large angular scales, yields only a small improvement and does not resolve the discrepancy. The authors interpret the results as further evidence that the low CMB quadrupole contributes importantly to the homogeneity anomaly, while emphasizing the need for more exhaustive analysis.
PublicThe cosmic microwave background appears to become statistically uniform across smaller angles on the sky than the standard cosmological model predicts. The researchers compared observations with simulated skies and found substantially better agreement when they removed the broadest patterns, especially one called the quadrupole, from both. They also tested whether a foreground signal associated with nearby galaxies could explain the mismatch by excluding affected regions. That helped only slightly and did not resolve the disagreement. The findings point to the unusually weak quadrupole as an important contributor to the anomaly, but further analysis is needed.
Young explorerScientists studied a sky map of light called the cosmic microwave background. It looks even across smaller parts of the sky than their model expects. When they left out some of the biggest patterns in both the real map and pretend maps made with the model, the maps agreed better. Hiding places that might be affected by nearby galaxies helped only a little. One big pattern that is unusually weak may be an important part of the puzzle, but scientists still need to check more carefully.
Ziwen Yin, Hanyu Cheng, Luca Visinelli
AstronomerThe authors constrain the initial abundance of evaporating primordial black holes with masses of approximately 3.2 × 10^13–5 × 10^14 g through their modeled effects on reionization. BlackHawk calculations track mass evolution and the full Hawking-emission spectrum, while DarkHistory propagates photons and electrons and computes energy deposition into IGM ionization, excitation, and heating. These effects enter a Gaussian Process reconstruction of the free-electron fraction using Planck low-multipole CMB polarization data, separating possible high-redshift energy injection from late-time astrophysical reionization. Consistency with the measured CMB yields upper abundance limits, not a PBH detection. The authors report that these limits are robust against reionization-modeling uncertainties and systematically more conservative than existing bounds, reflecting their fully numerical, time-dependent treatment.
PublicThis study uses measurements of the cosmic microwave background to limit how many small primordial black holes could have existed initially. Such black holes are predicted to release particles as they evaporate through Hawking radiation, potentially heating intergalactic gas and freeing electrons from atoms. The researchers calculate these effects and compare the resulting histories of free electrons with Planck observations, while allowing flexibility in how ordinary astrophysical sources reionized the gas later. They derive upper limits rather than detect primordial black holes. The authors report that their limits are less restrictive than earlier bounds but robust against uncertainties in modeling reionization.
Young explorerScientists wondered whether tiny black holes from the early universe could have given off energy and changed the gas between galaxies. They used computer calculations to work out how that might happen, then checked against measurements of very old light. They did not find these black holes. Instead, they worked out a limit on how many could have been there, while allowing for uncertainty about how the gas changed later.
Shubo Li, Moritz S. Fischer, Zixiang Jia+3 more
AstronomerThe study benchmarks the semi-analytical isothermal Jeans model against a high-resolution, isolated N-body simulation of a self-interacting dark matter halo evolving into deep core collapse. The model reproduces the density evolution through much of collapse but misses the sharp increase in central velocity dispersion. For strong-lensing quantities, including projected mass and logarithmic density slope, it follows the simulated evolution more closely than a parametric approach in the deep-collapse regime. This simulation-based comparison supports the model as a computationally efficient description of SIDM halo evolution, with a significant limitation in its central kinematics; it is not a test against observed lenses.
PublicResearchers tested a relatively fast mathematical model against a detailed computer simulation of a dark matter halo whose particles interact with one another as its core collapses. The model reproduced how the simulated density changed through much of the collapse, but missed a sharp increase in the spread of particle speeds near the center. It also tracked quantities relevant to gravitational lensing—how the halo bends light—more closely than another modeling approach during deep collapse. The results support the model's usefulness for efficient calculations, while revealing a limitation. The comparison used a simulation, not observations of an actual halo.
Young explorerScientists used a detailed computer simulation to follow a big cloud of dark matter as its middle squeezed tighter. They tested a simpler, faster way to describe it. The simpler way mostly matched how crowded the cloud became, but it missed how much more varied the speeds of the dark matter bits became near the middle. It also did better than another method at following clues about how the cloud would bend light. This was a computer test, not something they watched happen in the sky.
Luca Gomez Bachar, Cora Dvorkin, Alberto Daniel Supanitsky
AstronomerThis simulation study tests how CNN-based Galactic foreground cleaning generalizes beyond the foreground models used for training, a key concern for searches for primordial CMB B-mode polarization and inference of the tensor-to-scalar ratio. The authors train several CNN architectures on different foreground models and evaluate them on models excluded from training. They construct a statistical complexity hierarchy using variance, skewness, and Shannon entropy. In these tests, training on more complex foreground models reduces bias and improves precision on unseen models, while training on the simplest model can introduce systematic errors. The results identify limited generalization as a source of systematic uncertainty; they do not demonstrate performance on real data or a detection of primordial B-modes.
PublicA particular polarization pattern in the cosmic microwave background, called primordial B-modes, would be strong evidence for gravitational waves from the early universe. Finding it requires accurately removing polarized emission from our own Galaxy. This study uses simulated data to test whether neural networks trained to remove that emission can handle Galactic models they have not seen before. Networks trained on statistically more complex models produced less biased and more precise results in these tests, while training on the simplest model could cause systematic errors. The findings highlight a risk that needs to be understood before these methods are applied to real observations; they are not a detection of the sought-after signal.
Young explorerScientists want to find a special pattern in very old light from space, but light from our own galaxy gets in the way. They taught computers to separate the light using pretend skies, then tested them on different pretend skies. Computers that practiced with more complicated examples did better on the new examples. Practicing with only the simplest examples could lead to mistakes. Scientists still need to understand those mistakes before using this method on real sky pictures.
Tiago Sinde, José Fonseca
AstronomerThis study forecasts whether combining photometric galaxy surveys with HI intensity mapping can jointly constrain the galaxy magnification bias s^G(z) and the Weyl-potential amplitude parameter β. Using a Fisher-matrix analysis, the authors consider DES-like, LSST-like and Euclid-like surveys, individually and paired with MeerKLASS or SKAO over overlapping sky areas. Relative to galaxy surveys alone, the multi-tracer combinations are forecast to improve constraints on β by factors of 18–50, depending on the surveys; improvements for s^G(z) range from marginal to factors of 2–4. Cross-correlations between tracers break parameter degeneracies, allowing simultaneous constraints. These are forecasts, not measured constraints, and suggest an additional route to constrain Φ+Ψ and test general relativity on cosmological scales.
PublicGravity bends light, subtly changing the apparent distribution of galaxies. This study asks whether combining galaxy surveys with maps of neutral hydrogen could help extract that lensing signal and test gravity across the Universe. The researchers use a statistical forecasting method rather than report new measurements. For the survey combinations studied, they predict constraints on a parameter describing the gravitational potential responsible for lensing could become 18–50 times tighter than with galaxy surveys alone. Improvements in parameters describing how galaxy counts respond to magnification range from small to factors of 2–4. Comparing the two kinds of maps helps separate effects that are difficult to distinguish using galaxy surveys alone. The forecasts point to a promising additional test of general relativity, rather than an actual test result.
Young explorerGravity can bend light, making the pattern of faraway galaxies look a little different. Scientists asked whether putting a galaxy map together with a map of hydrogen gas could help them understand that bending better. Their calculations suggest that using both maps could work much better than using the galaxy map alone. They have not measured this improvement yet. If it works as predicted, it could help check our ideas about how gravity works across the Universe.
Yiheng Liu, Xinyu Li
AstronomerSimulations of stellar-cluster evolution in fuzzy dark matter (FDM) halos show that tidal heating dominates at sufficiently low particle masses, when the de Broglie wavelength greatly exceeds the cluster size. Earlier simulation-based lower mass bounds used a diffusion approximation valid only when that wavelength is much smaller than the galaxy’s half-light radius. The new simulations also find that a reduced soliton mass and a tidally stripped halo can suppress heating. Constraints on FDM particle mass from cluster heating therefore require careful treatment of halo structure and environment; the abstract reports no revised numerical bound.
PublicGroups of stars in ultra-faint dwarf galaxies could help test fuzzy dark matter, a model in which dark matter behaves like waves. Earlier simulations used an approximation that applies only when those waves are much smaller than the galaxy’s half-light radius. New simulations find that, for sufficiently low dark matter particle masses, the waves are much larger than the star cluster and tidal forces become the main source of stellar heating, or changes in the stars’ motions. They also show that a less massive central dark matter core and a surrounding halo stripped by tidal forces can reduce this heating. The findings mean that using star clusters to constrain the particle mass requires accounting for the dark matter halo’s structure and surroundings.
Young explorerScientists used computer models to see how groups of stars might move inside dark matter that acts like waves. In some models, the waves were much bigger than the star group, and uneven pulls were the main thing stirring the stars around. Changing the dark matter around the stars could make the stirring weaker. So scientists need to understand those surroundings before using the stars to learn about this possible kind of dark matter.
A. Novelli, F. Piacentini, S. Micheli+97 more
AstronomerThe authors present an iterative algorithm for relative cross-calibration of detectors within a CMB frequency band, comparing single-detector maps with band maps. It can address calibration parameters correctable by map-level reprocessing. Validation uses simulated LiteBIRD polarisation maps, not observations. For both random individual-detector angle errors and rotations of entire detector wafers, the algorithm converges to the correct relative calibration and corrects detector polarisation-angle miscalibrations with arcminute precision. Absolute calibration remains a separate step, addressable through ground measurements or E-B nulling. Propagating residual calibration uncertainties through component separation and tensor-to-scalar ratio estimation with both FgBuster and HILC yields induced biases in r well below LiteBIRD's maximum systematics budget of 6.5 × 10^-6. These simulation results support the method's suitability for high-precision CMB experiments.
PublicA new method aims to make detectors measuring the cosmic microwave background agree with one another more accurately. It repeatedly compares each detector's sky map with a combined map from detectors observing the same frequency band. In simulated data for the upcoming LiteBIRD experiment, the method successfully corrected relative errors in the detectors' polarisation angles, whether errors affected individual detectors or whole detector wafers. The corrections reached arcminute precision. Remaining errors produced biases well below LiteBIRD's allowed systematic-error budget in two analysis approaches. These are simulation results, not a demonstration with observed data. The method aligns detectors relative to one another; establishing their absolute angle calibration still requires a separate step.
Young explorerImagine several sky cameras that need to agree about which way a light pattern points. Scientists made a computer test for a future experiment called LiteBIRD. Their method compared pretend sky pictures and fixed small differences between the cameras. It worked well in those tests, but it has not yet been shown here using real sky pictures. Making the cameras agree still leaves a separate job: checking that they all point the right way.
Paula S. Ferreira, Carlos A.P. Bengaly, Renyue Cen
AstronomerAngular auto- and cross-power spectra from DES and DESI Legacy Imaging Surveys DR8 show stronger clustering of elliptical than spiral galaxies. The authors introduce the cross-tracer clustering ratio (CTCR), an auto-to-cross-spectrum ratio probing scale-dependent relative clustering. DESI provides the cleanest constraints because the tracers have well-matched redshift distributions. The inferred relative bias is near unity at multipoles ℓ ≲ 50 and increases toward smaller angular scales; at ℓ = 200, the difference reaches 2.9–4.0σ per bin, with an inverse-variance-weighted amplitude Δb = +0.56 ± 0.06. A complementary linear-bias analysis finds ellipticals positively biased relative to matter, while spirals are consistent with weak bias or anti-bias. Checks include two covariance estimators, contamination tests, luminosity splits, and comparisons with two N-body mock catalogs. Crucially, CTCR is treated as an effective clustering ratio that bounds the physical bias ratio from above, not as a direct measurement of that ratio. Extracting the physical ratio through a joint multi-spectrum decomposition remains future work. The results provide empirical evidence for morphology-dependent clustering and offer an observable for future tests of halo occupation and assembly-bias models.
PublicGalaxy shape is linked to how strongly galaxies cluster together, according to measurements from two imaging surveys. Elliptical galaxies cluster more strongly than spiral galaxies, with the clearest evidence coming from the DESI survey sample, where the two groups have well-matched distance distributions. Their clustering is similar on large angular scales, but the difference grows on smaller scales. The researchers introduced a statistic that compares clustering within each galaxy type with clustering between the two types, and checked the findings using several tests and comparisons with simulated catalogs. An important limitation is that this statistic gives an upper bound on the underlying ratio of clustering strengths, rather than measuring it directly; a fuller analysis is still needed. The findings could help test models of how galaxies occupy dark matter halos and how their clustering relates to their formation histories.
Young explorerGalaxies are huge groups of stars. Some look like smooth ovals, and others have spiral shapes. Scientists looked at sky pictures and found that the oval galaxies bunch together more strongly than the spiral ones. The difference is clearer when they look at smaller patches of sky. Their measuring tool puts a limit on how big the true difference can be, but more work is needed to find that difference exactly.
Aditya Kulkarni, Lorenzo Sorbo
AstronomerThis analytical study examines the onset of strong backreaction in models coupling an axion-like inflaton to a U(1) gauge field. A Laplace transform recasts an integro-differential equation as a search for poles of an analytic function. The analysis confirms a stable region of strong backreaction previously found with a different formalism and provides what the authors describe as the first analytical formulae for studying evolution from weak to strong backreaction. These are theoretical results, not observational findings, and the strong-backreaction regime remains incompletely understood.
PublicThe researchers study a theoretical model in which the field driving cosmic inflation interacts with another field. The second field can push back strongly enough to affect the first field’s motion. Using a mathematical technique called a Laplace transform, the authors confirm earlier theoretical work indicating that this strong feedback can have a stable regime. They also present what they describe as the first analytical formulas for following the transition from weak to strong feedback. The study develops the theory rather than testing it against observations, and the strong-feedback behavior is still not fully understood.
Young explorerImagine two things that can push on each other. Scientists used math to study a model of the very early universe where one thing starts pushing back strongly on the other. Their math supports an earlier finding that strong pushing can sometimes stay steady. They also made new math tools to study how a small push becomes a big one. This is a model, not something they watched happen in the sky, and there is still more to understand.
Jose Mathew
AstronomerThis theoretical study tests potential slow-roll (PSR) approximations to the Hubble-flow hierarchy in Starobinsky inflation. The authors map analytic Jordan-frame background variables into the Einstein frame and derive Hubble-flow parameters directly. Their leading background exactly solves a controlled deformation of the Starobinsky action; linearizing the pure Starobinsky equation about it supplies a closed-form perturbative correction. With the same first-order spectral expressions used throughout, the corrected background follows the numerical evolution of the first two Hubble-flow parameters more accurately than next-to-leading-order PSR over their common physical domain. The NLO estimate of the first parameter peaks near 0.114 and then declines, preventing it from identifying inflation's endpoint through the condition that this parameter equals one. For the Planck 2018 central spectral-index value of 0.9649, the corrected background gives an e-fold number of approximately 55.60, versus 55.72 numerically and 56.98 from the conventional large-e-fold estimate. For the adopted ACT DR6 combined-data value of 0.974, it gives approximately 75.43 versus the conventional 76.92. These are model calculations conditioned on the stated spectral-index values, not new observations; the construction provides a self-consistent endpoint and an accurate first-order e-fold estimate in the numerical comparison reported.
PublicThe paper examines how accurately a mathematical shortcut describes Starobinsky inflation, a model of rapid expansion in the early universe. The researchers build an improved analytic description and compare it with numerical calculations of the model. Their corrected description follows two quantities governing the expansion more closely than a commonly used approximation, within the range where both approaches remain physically meaningful. The usual approximation also fails to identify the end of inflation using the standard condition examined here. Using a Planck 2018 value describing the primordial fluctuation spectrum, the improved calculation gives an expansion count of about 55.60 e-folds, close to the numerical result of 55.72; the conventional estimate is 56.98. An e-fold measures expansion by a fixed multiplicative factor. The authors also calculate a different expansion count using an adopted ACT DR6 combined-data value. These results improve calculations within this inflation model; they are not new observations or proof that the model describes the universe. The estimates retain a first-order approximation for the fluctuation spectrum.
Young explorerScientists use math to explore an idea that the very young universe grew very quickly. A usual math shortcut does not follow this model well enough to tell when that fast growing ends. The researchers made a better calculation and checked it against a computer calculation. Their new answer came much closer in the comparison they made and could mark the end of the fast growing in the model. This is a better way to work out the idea, not proof that the universe really grew that way.
Danny Marfatia, Ye-Ling Zhou
AstronomerThis phenomenological study compares predicted gravitational-wave spectra from cosmic gauge string networks and superstring networks containing multiple string types. It examines how departures from scaling and changes in the early Universe’s relativistic degrees of freedom affect the spectra, and derives analytical expressions valid across frequencies relevant to pulsar timing arrays (PTAs) and laser interferometers. Comparing models with PTA observations, the authors find superstring networks consistent with NANOGrav data at 32 nHz but excluded at 3σ by data at 3.2 nHz unless the string coupling g_s < 0.2 or the strings evolve within only about 10% of the higher-dimensional volume. Gauge string networks are excluded at 3σ by NANOGrav-15 data but remain fully compatible with EPTA and PPTA data. The study also examines correlations between predicted signals at PTA and laser-interferometer frequencies. These are model-dependent constraints and compatibility tests, not detections of cosmic strings.
PublicCould hypothetical cosmic strings produce the gravitational waves studied by pulsar timing arrays? This paper compares predictions for two kinds of string networks, including superstrings with multiple string types. The calculations account for changes in the early Universe and provide formulas covering frequencies relevant to pulsar timing arrays and laser interferometers. The comparison with observations gives mixed results: superstrings fit NANOGrav data at one frequency but are strongly disfavored at a lower frequency unless their coupling is small enough or they occupy only about a tenth of the higher-dimensional space. Another type, gauge strings, is strongly disfavored by NANOGrav-15 but compatible with EPTA and PPTA data. The study tests possible explanations; it does not establish that cosmic strings exist.
Young explorerScientists wonder whether tiny, thread-like things in space could make ripples in space itself. They worked out what ripples different kinds of threads might make and compared those ideas with measurements. Some measurements fit the ideas, while others do not unless the threads behave in special ways. This does not mean anyone has found these threads.
Sougata Bhunia, Goutam Manna, Eduardo Guendelman+3 more
AstronomerThe authors study linearized, transverse-traceless tensor propagation in k-essence cosmology, with a non-canonical scalar field describing the dark sector. In the high-frequency limit on an FLRW background, they derive a modified evolution equation with strictly luminal GW speed, compatible with GW170817, and a time-dependent effective mass induced by the background scalar field. This term modifies the dispersion relation and produces an accumulated, frequency-dependent phase shift over cosmological distances without adding propagating degrees of freedom. Within the model, the effective mass is uniquely fixed by background cosmological parameters and can be reconstructed as m_eff(z). The GW and electromagnetic luminosity distances remain identical. A joint Bayesian analysis uses cosmic chronometers, BAO, Pantheon+SH0ES, and GWTC-2.1/3/4 standard-siren measurements, with fit and model performance assessed through chi-squared statistics, AIC, BIC, and DIC. The reconstruction is consistent with current data, reproduces late-time expansion, and constrains m_eff(z); the abstract does not report a detection of the predicted phase shift or establish preference over alternative models.
PublicThis theoretical study asks how gravitational waves would travel through a universe whose dark sector is described by an unconventional scalar field. In the short-wavelength approximation used by the authors, the waves retain the speed of light, but the evolving cosmic background gives their propagation an effective mass term. The model predicts that this term changes the waves’ accumulated phase—the timing of their oscillations—in a frequency-dependent way over cosmic distances, without adding new kinds of propagating waves. It also preserves agreement between distances inferred from gravitational waves and from light. The authors compare the model with several sets of cosmic-expansion and gravitational-wave data. They find it consistent with current observations and constrain how the effective mass could evolve, rather than reporting a direct detection of the predicted phase change.
Young explorerGravitational waves are tiny ripples in space. Scientists used math to explore how an invisible field might affect them as the universe grows. In their model, the ripples still travel at the speed of light, but the pattern of their wiggles can shift during a very long trip. Today’s measurements fit this idea, but that does not mean scientists have seen the predicted shift.
Yoann Launay
AstronomerThis theoretical work extends stochastic inflation beyond full General Relativity to a broad class of fully nonlinear scalar-tensor theories. The authors apply a gauge-agnostic coarse-graining procedure to the linear equations of the associated effective field theory to determine stochastic sources. Identifying the effective-theory coefficients then maps each theory to its stochastic equations of motion. Examples include Gauss-Bonnet, generalized Brans-Dicke, Horndeski, and braiding theories, with most examples described as unprecedented. The authors also demonstrate coarse-graining for multifield inflation in full General Relativity. Further extensions toward a phenomenologically complete framework are discussed rather than established, and applications beyond inflation are argued to be possible. No observational tests are reported.
PublicDuring the proposed early period of rapid cosmic expansion called inflation, tiny quantum fluctuations can be stretched to enormous scales and behave like classical disturbances. This theoretical study broadens a method that represents their influence using random sources in equations describing the universe. The authors show how to construct these equations for several theories that extend General Relativity, and also demonstrate the averaging procedure for inflation involving multiple fields within General Relativity. These are mathematical developments, not observational discoveries. A more complete framework and uses beyond inflation remain directions for further work.
Young explorerScientists study an idea that the baby universe grew very fast, stretching tiny wiggles into huge ones. They made new math recipes that use a little randomness to describe those wiggles in different theories of the universe. This is work with equations, not something newly seen in the sky.
Eugenio Megias, Miguel Prieto, Mariano Quiros
AstronomerThis theoretical study explores two possible dark-matter components in a warped extra-dimensional brane-world cosmology with a linear dilaton background and a gapped graviton continuum. Self-energy radiative corrections can generate an isolated massive-graviton resonance, proposed as a long-lived, feebly interacting dark-matter candidate produced through freeze-in. The authors find that this candidate satisfies theoretical and experimental constraints in the sub-MeV mass range within their framework. They connect its existence to a brane-localized inflaton of mass around 10^11 GeV and a sub-TeV reheating temperature, in an inflationary scenario capable of reproducing recent cosmological observables. Separately, they identify the graviton continuum, a five-dimensional realization of unparticle physics, as a holographic fluid that could constitute dark matter. Its ultraviolet freeze-in abundance depends mainly on the reheating temperature. The mass gap and reheating temperature determine whether one or both components can be present; these are theoretical possibilities, not dark-matter detections.
PublicCould dark matter take two different forms in a universe with an extra dimension? This theoretical study explores that possibility rather than reporting a detection. One proposed form is a very light, long-lived particle associated with gravity, produced gradually through extremely weak interactions in the early universe. The authors find that it can meet theoretical and experimental constraints within their model, and link it to a proposed explanation of the universe's early rapid expansion. The other possible form is a continuous range of gravity-related states that collectively behave as a fluid. How much of this fluid forms depends mainly on the temperature reached when the universe reheats after that expansion. Depending on this temperature and the minimum mass of the continuous states, the model could contain either one or both kinds of dark matter.
Young explorerScientists are exploring a mathematical idea about dark matter, the invisible stuff in space. Their idea includes an extra direction in space and could make two kinds of dark matter: one kind made of tiny particles, and another that acts like a fluid. Whether there could be one kind or both depends on conditions when the universe was very young. This is an idea they are studying, not something they have found.
Hansong Zhang, Huai-Ke Guo, Mairi Sakellariadou+2 more
AstronomerThis work formally unifies discrete harmonic and continuous burst-superposition descriptions of the gravitational-wave background from cosmic-string loops. The representations converge on the scale-invariant spectral plateau but diverge along the rising low-frequency branch, where the first few harmonics make discreteness important. The authors apply this framework in joint Bayesian inference using NANOGrav, EPTA, and LIGO–Virgo–KAGRA data across four representative loop-distribution models, jointly sampling string tension Gμ and average cusp and kink numbers to account for loop-radiation uncertainties. Using the harmonic expansion strengthens the LVK bounds by 21%–31% for three models. The LVK constraints also prevent three of the four models from explaining the observed PTA common signal. For the remaining model, the multi-band analysis improves the inferred upper limit on Gμ. These are model-dependent constraints, not a detection of cosmic strings.
PublicThe researchers connect two mathematical ways of predicting gravitational waves from cosmic-string loops. The methods agree on a flat part of the predicted spectrum but differ at low frequencies, where treating the radiation as distinct harmonics matters. They then combine pulsar-timing and LIGO–Virgo–KAGRA data to test four models of how cosmic-string loops are distributed, allowing for uncertainty in how the loops radiate. Using the harmonic calculation tightens the LIGO–Virgo–KAGRA constraints by 21%–31% for three models. Those data also rule out three of the four models as explanations for the shared signal seen in pulsar-timing measurements. The remaining model receives a tighter limit on string tension; it is not confirmed as the signal’s source.
Young explorerScientists studied whether tiny loops of possible space strings could make ripples in space. They showed how two ways of calculating those ripples fit together, and where they differ. Then they checked four ideas about the loops against telescope data. Three could not explain a shared signal in measurements of pulsing stars while still fitting the other data. One idea is still possible, but this does not show that space strings are real.
