Abhiram Cherukupalli, Vincent S. H. Lee, Kim V. Berghaus+1 more
AstronomerThe study proposes differencing timing residuals of sub-parsec pulsar pairs to suppress the nanohertz gravitational-wave background while retaining differential perturbations from nearby dark matter subhalos. Its analysis finds that pairs separated by 0.1 pc improve sensitivity to subhalos of roughly 10^-6 solar masses by more than an order of magnitude compared with an otherwise identical array of widely separated pulsars. Dense globular clusters naturally provide many close pairs, but perturbations from their baryonic environment must be distinguished from dark matter signals. This is a sensitivity finding, not a reported subhalo detection.
PublicClosely spaced pulsars could help astronomers search for tiny clumps of dark matter. A background of gravitational waves affects the timing of both pulsars almost equally, so comparing their timing differences can suppress that interference. A nearby dark matter clump would affect the two differently, leaving a signal. The study finds that pairs 0.1 parsec apart could improve sensitivity to clumps about a millionth of the Sun’s mass by more than tenfold. Dense star clusters contain many suitable pairs, but effects from ordinary matter must also be separated out; no dark matter detection is reported.
Young explorerPulsars are stars that send out regular flashes, like ticking clocks. Scientists suggest comparing two very close together to cancel a shared wobble and look for a different wobble from an invisible clump of dark matter. Ordinary stuff nearby could make wobbles too. They have not found a clump this way yet.
Sangjun Cha, Marceau Limousin, M. James Jee
AstronomerThis study tests whether allowing cluster-scale dark matter halos to be offset from brightest cluster galaxies improves strong-lensing predictions for Abell 370, RX J1347.5-1145, and MACS J0416.1-2403. MrMARTIAN models combine analytic mass profiles with a regularized grid; fixed and free halo-position models are compared across regularization weights using jackknife predictions for excluded source systems. Mean RMS values agree within bootstrap uncertainties, and median paired differences remain near zero, indicating comparable predictive accuracy. Broadly similar total mass distributions can yield different fitted halo offsets as regularization changes, demonstrating a non-unique mass decomposition. Within this framework and for these three clusters, the data do not require offsets to improve predictive accuracy; this does not establish that physical offsets are absent. The results caution against interpreting fitted halo positions alone as evidence about cluster dynamics or dark matter physics. Model dependence in magnification and time-delay estimates can also affect inferred high-redshift source properties or the Hubble constant.
PublicGalaxy clusters bend the light of galaxies behind them, allowing astronomers to model where the clusters' mass lies. This study asks whether models predict that bending better when they allow the main dark matter concentrations to sit away from the brightest cluster galaxies. For three clusters, the researchers tested predictions for background galaxies left out of the model fitting. Models with and without these offsets performed comparably within the uncertainties. Although the overall mass maps stayed broadly similar, the fitted offsets changed with modeling choices, showing that the same mass distribution can be divided among model components in different ways. In these clusters and with this modeling framework, offsets were not needed to improve predictions—not proof that real offsets cannot exist. The findings caution against drawing physical conclusions from fitted dark matter positions alone. Modeling choices can also affect estimates of background galaxies' intrinsic properties and the universe's expansion rate.
Young explorerBig groups of galaxies bend light from galaxies behind them. Scientists use that bent light to make maps of matter they cannot see. They tried two kinds of maps for three galaxy groups: one kept the main invisible matter clumps lined up with the brightest galaxies, and the other let them move away. Both kinds made about equally good guesses for light patterns they had not used to build the maps. Changing how the maps were made also changed where some invisible clumps seemed to sit. So a clump's place on a map may depend on how the map is made, and does not by itself tell us exactly where the real clump is.
Yifei Zhao, Jailson Alcaniz, Humberto A. Borges+2 more
AstronomerMotivated by the Hubble-constant tension, indications of dynamical dark energy, and swampland challenges to stable de Sitter vacua, the authors investigate an interacting Λ model with a general linear dark-sector coupling. They derive analytic background solutions and perturbation equations, assess physically acceptable parameters, and constrain the model using DES-Dovekie type Ia supernovae, DESI BAO, and CMB data. Their analysis suggests an allowed parameter region in which dark energy density changes from negative to positive while dark matter density remains positive. This motivates further study of an interaction-driven anti-de Sitter-like to de Sitter-like transition, rather than establishing that such a transition occurred.
PublicSome cosmological findings raise questions about whether the standard model of the universe is complete. This study explores an alternative in which dark matter and dark energy interact, allowing dark energy density to change from negative to positive. The researchers develop the model mathematically and compare it with supernova, galaxy-distance, and cosmic microwave background data. Their analysis suggests that such a change could be compatible with the data while keeping dark matter density positive. It does not demonstrate that the universe actually underwent this transition.
Young explorerScientists are testing an idea about how the universe changes. In their idea, two invisible ingredients, called dark matter and dark energy, can share energy. Their calculations let the amount of dark energy switch from a negative number to a positive one, while the amount of dark matter stays positive. They checked the idea against information from space, and it may work—but they have not shown that this switch really happened.
David Wittman, Rodrigo Stancioli, Christopher Hopp
AstronomerThe study assesses whether optical spectroscopy can detect the relativistic moving lens effect, in which a lens’s transverse motion shifts the wavelengths of lensed photons. Comparing multiple strongly lensed images of the same source could isolate this signal from much larger cosmological and Doppler shifts; a massive, rapidly moving cluster lens could produce relative wavelength differences of up to one part in a million. Keck/Deimos observations of the merging cluster RM J001938.7+033557.3 provide a feasibility case study, not a reported detection. The authors also quantify predicted transverse motions for likely merging-cluster systems in ΛCDM and find that a moving-lens measurement could distinguish outbound motion after first pericenter from a return to the same separation after first apocenter.
PublicA moving galaxy cluster can slightly change the wavelengths of light that its gravity bends from a distant source. The predicted change is extremely small, but comparing several gravitationally magnified images of the same source could reveal it. This study uses Keck/Deimos observations of a merging galaxy cluster to examine whether optical spectroscopy could measure the effect; it does not report a detection. For a massive, fast-moving cluster, the images’ wavelengths could differ by as much as one part in a million. Such a measurement could help determine whether two merging clusters are moving apart after their first close encounter or returning after reaching their greatest separation.
Young explorerA big group of galaxies can bend light and make us see more than one picture of the same faraway thing. If the group moves across the sky, it might change the light’s color by a tiny amount. Scientists studied whether they could spot that tiny change by comparing the pictures, but they have not reported finding it. If they can measure it, it could help them tell whether two groups of galaxies are moving away from each other or coming back together.
Purba Mukherjee, Arman Shafieloo, Varun Sahni+1 more
AstronomerThe authors test metastable dark energy on the minimal phantom brane using CMB observations, DESI DR2 BAO measurements, and DES-Dovekie Type Ia supernova data. They consider exponential DE decay (M1), decay into non-baryonic dark matter (M2), and decay into dark radiation (M3), comparing these with ΛCDM, CPL, and a phantom-brane model with non-decaying Λ. The inferred Γ/H₀ values are 0.362 ± 0.086, 0.539 ± 0.125, and 0.483 ± 0.112, respectively. Relative to ΛCDM, the models yield Δχ²_MAP = −17.14, −18.76, and −18.22 and ΔDIC = −8.66, −9.63, and −6.56. In these models, braneworld screening produces effective w < −1 at z ≳ 0.4, while decay drives w > −1 nearer the present, with crossing at z ≃ 0.3–0.4. The analysis favors these models over ΛCDM for the adopted data and presents a mechanism consistent with DESI hints, rather than establishing dark-energy decay or braneworld physics observationally.
PublicDark energy is associated with the universe’s accelerating expansion, but its nature remains uncertain. This study tests three models in which dark energy can decay, within a framework that modifies how gravity affects cosmic expansion. The models allow dark energy’s effective behavior to move across a boundary called the phantom divide: gravity-related effects dominate earlier, while decay becomes important closer to today. Using cosmic microwave background observations, DESI measurements, and supernova data, the researchers find that all three models fit the combined data better than the standard model with constant dark energy. This offers a possible explanation for DESI’s hints of changing dark energy, but does not demonstrate that dark energy actually decays or that the proposed gravity framework is correct.
Young explorerThe universe is getting bigger faster and faster. Scientists use the name dark energy for something linked to that speeding up. These scientists tried three ideas in which dark energy slowly fades or turns into other invisible things, together with a different way for gravity to work. Their ideas matched the space clues better than an idea where dark energy stays the same. That makes them interesting possibilities, but we do not yet know whether they are what really happens.
Kazuya Furusawa, Hiroyuki Tashiro
AstronomerThis theoretical study computes the intensity and circular polarization of an isotropic stochastic gravitational-wave background sourced by the anisotropic stress of helical primordial magnetic fields in phenomenological parity-violating inflationary magnetogenesis models. For several assumed magnetic-field power spectra, it uses the planned LISA-TAIJI network sensitivity to calculate signal-to-noise ratios and Fisher parameter forecasts. The authors forecast that the helical-to-non-helical power ratio r_H could be estimated with circular-polarization SNR greater than 2 for field strengths of roughly 10 nG or more for a delta-function-type spectrum, or 50 nG or more for a scale-invariant-type spectrum. These conditional forecasts, not detections, provide a prospective constraint criterion at k_LISA approximately 10^12 Mpc^-1.
PublicMagnetic fields from the very early universe could have produced a background of gravitational waves, or ripples in spacetime. If those fields had a preferred twist, the waves could favor one direction of circular polarization. The researchers calculate this possible signal for several assumed patterns of magnetic-field strength across different scales, then forecast what the planned LISA-TAIJI detector network might learn. Their calculations suggest that sufficiently strong fields could allow the network to estimate how much of the magnetic-field power has this preferred twist. The required strength depends on the assumed pattern: roughly 10 or 50 billionths of a gauss for two cases studied. This is a forecast based on models and planned sensitivity, not an observation of ancient magnetic fields or their waves.
Young explorerScientists wonder whether magnetic fields when the universe was very young made tiny ripples in space. If the fields had a special twist, the ripples might carry a clue about it. The scientists used calculations to see whether planned space detectors could find that clue. They think it might be possible if the fields were strong enough, but they have not found these ripples yet.
Fumiya Okamatsu, Tomo Takahashi, Shuichiro Yokoyama
AstronomerThis study assesses the prospective ability of Dark Ages 21 cm power-spectrum observations to constrain the scale dependence of the primordial power spectrum and discriminate among inflationary models beyond scales accessible to current CMB observations. Models with unconventional scale dependence could be stringently tested, whereas models predicting nearly identical running spectral indices may remain difficult to distinguish. Combining future 21 cm measurements with CMB data is projected to improve constraints significantly, even for a moderate observational configuration. The study also examines how the choice of pivot scale affects the constraints; these are prospective capabilities, not results from new observations.
PublicThe study explores how future measurements of a radio signal from the universe’s early Dark Ages could test theories of inflation, its proposed early expansion. Patterns in this 21-centimeter signal could reveal how primordial fluctuations vary across scales beyond the reach of current cosmic microwave background observations. The analysis suggests that theories with unusual scale dependence could be tested strongly, but theories with very similar changes across scales might still be hard to tell apart. Combining the future radio measurements with cosmic microwave background data could improve the tests, even with a moderate observing setup. The study also considers how the reference scale used in the analysis affects the constraints.
Young explorerScientists want to use a radio signal from when the universe was very young to learn about its tiny early bumps. Future measurements might help them check different ideas about how the universe grew so fast at the beginning. Some ideas may look too much alike to tell apart. Using this signal together with another kind of light from the young universe could help. These are things scientists think future measurements could do, not things they have already seen.
D. Sanchez-Cid, J. Sanchez, I. Sevilla-Noarbe+19 more
AstronomerThe authors present the first fully photometric harmonic-space 3×2pt analysis using LSST-DESC pipelines on HSC Year 1 data, combining cosmic shear, galaxy clustering, and galaxy–galaxy lensing angular power spectra. They perform null tests, use mode deprojection to mitigate observing-condition effects on density and shear fields, and reproduce the official HSC Y1 cosmic-shear constraints with the DESC inference code. They constrain ΛCDM and wCDM using individual and combined probes. The joint ΛCDM analysis yields Ωm = 0.249 (+0.061/−0.051), σ8 = 0.904 (+0.098/−0.091), and S8 = 0.821 (+0.018/−0.021). HSC Y1 has depth and galaxy density similar to those expected for LSST Year 1, making this a survey-data validation of the complete DESC 3×2pt infrastructure rather than an analysis of LSST observations.
PublicResearchers combined three clues from Hyper Suprime-Cam images: how galaxies cluster, how gravity distorts their apparent shapes, and how those distortions relate to foreground galaxies. Together, these measurements constrain how much matter the universe contains and how strongly it is clumped, within the cosmological models tested. The team checked its analysis and corrected for effects of observing conditions. Because these images resemble the depth and galaxy density expected from LSST’s first year, the study provides a real-data test of the tools intended for that future analysis; it does not report LSST results.
Young explorerGravity can bend light and make faraway galaxies look a little stretched. Scientists studied those shapes and where galaxies gather together to learn about how much matter is in the universe and how it bunches up. They also checked their tools for mistakes. They used pictures already taken to get ready for studying new pictures from LSST.
Yuting Liu, Masamune Oguri
AstronomerThis reanalysis of the cluster-lensed quasar SDSS J1004+4112 and supernova Refsdal in MACS J1149.5+2223 replaces elliptical NFW main halos with cored elliptical NFW profiles and jointly infers H0 and the dimensionless core size beta = rc/rs. The brightest cluster galaxy (BCG) is treated using member-galaxy scaling relations or modeled separately with different stellar-mass priors. For SDSS J1004+4112, both beta and H0 depend strongly on the BCG treatment: an unconstrained BCG mass implies a large core, whereas a reasonable mass assumption favors a nearly cuspy halo with beta approximately 0.001. For MACS J1149.5+2223, beta is approximately 0.5 without a prior and 0.0410 (+0.0865, -0.0276) with a Salpeter-IMF stellar-mass prior. Its H0 constraint remains stable across BCG assumptions; the Salpeter-prior result is 65.9 (+3.5, -3.4) km/s/Mpc, with median shifts below one sigma. Translating core constraints into self-interacting dark matter cross sections yields sigma/m < 0.035 cm²/g at 95% confidence for SDSS J1004+4112 and 0.071 (+0.15, -0.045) cm²/g at 68% confidence for MACS J1149.5+2223. These are model-based inferences, with important sensitivity to BCG mass assumptions.
PublicGalaxy clusters bend light from objects behind them, producing multiple images whose light arrives at different times. Researchers reanalyzed two such systems to test how the assumed concentration of dark matter near each cluster’s center affects estimates of the universe’s expansion rate. They found that assumptions about the mass of the cluster’s brightest galaxy strongly affect the inferred dark matter core and expansion rate in one system. In the other, the expansion-rate estimate remained comparatively stable: one model gave about 66 km/s/Mpc. The inferred core sizes also provided constraints on how strongly dark matter particles might interact with one another, rather than a direct detection of those interactions.
Young explorerBig groups of galaxies bend light, so we can see the same faraway object more than once. Scientists used light arriving at different times to work out how fast the universe is growing. Their answers sometimes changed when they changed their guesses about a big galaxy and the invisible matter around it.
A. Holas, S. Taubenberger, C. Vogl+41 more
AstronomerUsing flux-calibrated, host-subtracted spectrophotometry of low-redshift SNfactory Type II-P supernovae, the authors improve expansion-velocity estimation with Gaussian Process regression and extend the standardized candle method with an H-alpha absorption-to-emission ratio correction in a hierarchical Bayesian framework. Standardization improves especially 30–40 days after explosion, reducing Hubble-flow scatter from 0.28 to 0.18 mag relative to previous work. With an existing Cepheid- or TRGB-calibrated SN II sample, they obtain H0 = 70.6 (+4.5/-4.3) km s^-1 Mpc^-1, with statistical uncertainty only and 6.2% precision, compared with 73.0 (+6.9/-6.1) km s^-1 Mpc^-1 and 8.9% precision without the added correction. Hierarchical-model variants shift H0 by 1.4 km s^-1 Mpc^-1, within the quoted statistical uncertainty. Differences between inferred calibrator and Hubble-flow parent populations remain unexplained by simple magnitude selection and require further attention as samples grow.
PublicThe researchers refined a way to use Type II-P exploding stars as distance indicators for measuring the universe’s expansion. Their method combines improved estimates of how fast the stellar material expands with a correction based on the balance of absorption and emission in a hydrogen spectral feature. In the observed sample, this made the distance indicators more consistent, especially 30–40 days after an explosion. Using supernovae with previously calibrated distances, they measured an expansion rate of 70.6 (+4.5/-4.3) kilometers per second per megaparsec, improving statistical precision from 8.9% without the new correction to 6.2% with it. Those error bars include only statistical uncertainty. The nearby calibration sample and the more distant comparison sample also show differences that the researchers have not fully explained, leaving an important issue for future work.
Young explorerExploding stars can help scientists work out how far away things are and how fast the universe is growing. But these stars do not all shine the same way. The researchers found a better way to compare one kind of exploding star by looking at its light and how fast its material moves. This made their answer about the universe’s growth more precise. They still found differences between the groups of stars they compared, so there is more to check.
Miguel Aparicio Resco, Florencia A. Teppa Pannia
AstronomerThis theoretical study connects the scale- and redshift-dependent correlation dimension D2 directly to a cosmological model's matter power spectrum. An analytical approximation using an effective filtering cut-off, k_cut = alpha/r with alpha approximately 2.39, reproduces the exact D2 to better than 1% for the representative cases considered. Nonlinear evolution generally reduces D2 relative to the linear prediction on small scales, especially at low redshift. Complementary derivative-based and variance-based sensitivity analyses in w0waCDM identify Omega_m as the dominant parameter for linear D2 and A_s for the nonlinear-to-linear ratio; w0 and wa alter the nonlinear contribution in scale- and redshift-dependent ways. These calculations provide a framework for characterizing clustering and the transition toward homogeneity, rather than an observational measurement.
PublicHow evenly is matter spread through the universe when we look over different distances and at different cosmic times? This study explores that question through cosmological calculations using a measure called the correlation dimension. The calculations show that nonlinear evolution generally makes matter appear more clustered on small scales than a simpler linear model predicts, with a stronger effect at more recent times. The researchers develop a shortcut that agrees with their exact calculation to better than 1% in the examples tested. They also examine how the measure responds to model parameters describing matter, initial fluctuations, and dark energy. The work offers a theoretical tool for studying cosmic structure, not a new observation of the universe.
Young explorerMatter in the universe is spread out in a lumpy pattern. Scientists used math to study how that pattern looks when they think about small pieces or very big pieces of space, and about different times. Their more detailed math usually gives a lumpier picture on small scales than their simpler math. They also found a math shortcut that worked very well in the examples they checked. This was a study using calculations, not a new picture taken of space.
Yu-Ning Wang, Paulo Montero-Camacho, Ziwei Wang+2 more
AstronomerThe study tests whether electromagnetic energy injection from dark matter decaying into electron–positron pairs can supply the additional reionization optical depth favored by the DESI DR2 BAO–CMB discrepancy. Using a simulation-calibrated Gompertzian astrophysical reionization model, it computes optical depth self-consistently from the free-electron history and jointly constrains cosmology, reionization, and decay rate with ACT+Planck CMB anisotropies, CMB lensing, BAO, and quasar damping-wing data. For a 1 GeV dark matter particle, including decay raises the marginalized optical depth from 0.064 to 0.072 without significantly improving the fit; the increase comes mainly from a broad dark-age ionization tail, not earlier astrophysical reionization. Across masses of 2 MeV–7 GeV, the central 68% credible intervals remain below approximately 0.08, a previously identified threshold for reducing both the neutrino-mass tension and the exclusion of ΛCDM below 2σ. The inferred lifetime constraints complement cosmic-ray and gas-heating bounds and compete with previous CMB limits. Within this model, allowed decay moves the optical depth in the desired direction but does not substantially alleviate the discrepancy.
PublicMeasurements of large-scale cosmic structure and the cosmic microwave background disagree in a way that could favor more scattering of ancient light by free electrons than microwave-background polarization indicates. The researchers tested whether dark matter decaying into electrons and positrons could add enough energy to free more electrons from atoms. Combining several kinds of astronomical data with a model of how the universe became ionized, they found that allowing these decays modestly raises the inferred amount of scattering, but does not significantly improve agreement with the data. In the model, the extra free electrons appear mainly over a long stretch of the cosmic dark ages, rather than because ordinary astrophysical reionization begins earlier. Across the particle masses studied, the permitted increase is too small to substantially resolve the discrepancy. This is a constraint on a proposed explanation, not a detection of dark matter decay.
Young explorerVery old light and the way galaxies are spread out give scientists clues about the universe, but the clues do not quite agree. Scientists tested an idea: could invisible dark matter break apart and give atoms enough energy to let tiny electrons loose? Those electrons could scatter the old light. Their model allowed a little more scattering, but not enough to make the clues agree much better. They did not discover dark matter breaking apart; they tested whether that idea could help.
Milad Noorikuhani, Jeremy Tinker
AstronomerThe authors present a fast method for assigning subhalos to simulated dark matter halos using a high-resolution reference simulation with the same cosmology but arbitrary initial conditions. A classifier built on a decision tree regressor predicts whether each target halo hosts any subhalo above a specified mass threshold. Predicted hosts are then matched to reference hosts through a nearest-neighbor search over selected halo properties, and their subhalos are mapped to the targets. Tests assess subhalo abundances, distributions, and three-dimensional and projected two-point correlation functions; prediction errors are well below 5% in most cases, not universally. The method can populate low-resolution simulations and investigate correlations of halo properties with subhalo abundance and clustering, supporting galaxy-halo modeling without resolving every subhalo directly.
PublicDetailed computer simulations of dark matter can reveal smaller clumps inside larger ones, but running many such simulations is expensive. This study presents a shortcut: predict which large clumps should contain smaller ones, find similar large clumps in a detailed reference simulation, and transfer their smaller-clump patterns. The reference and target simulations must use the same cosmological model, though their starting arrangements can differ. In simulation tests, errors in predicted counts, distributions, and clustering were well below 5% in most cases. The method could help build simulated galaxy catalogs and explore how the properties of large dark matter clumps relate to the smaller clumps they contain; these are simulation results, not observations of the sky.
Young explorerScientists make pretend universes on computers. These have big clumps of invisible dark matter, sometimes with little clumps inside. Making all the tiny details takes lots of computer work. The scientists made a shortcut that guesses which big clumps need little ones, then copies a pattern from a similar clump in a more detailed pretend universe. In most tests, the shortcut was close to the detailed answer, but it was not perfect.
Thomas Essinger-Hileman, Caleigh Ryan, Yunyang Li+25 more
AstronomerCLASS combines 90, 150, and 220 GHz observations with previous 40 GHz results to tighten constraints on CMB circular polarization, Stokes V. The multifrequency analysis improves upper limits by approximately a factor of five at 10 < ℓ < 30 and extends constraints to ℓ = 700. It also constrains atmospheric circular polarization across all CLASS frequencies and compares these constraints with an atmospheric spectral model. Combining CLASS with Planck temperature data yields the first limits on the TV power spectrum. Both VV and TV spectra are consistent with zero: the reported VV upper limit is 5.4 × 10⁻³ μK_CMB² at 10 < ℓ < 30, while the TV upper limit is 5.8 × 10⁻¹ μK_CMB² at 95% confidence for 30 < ℓ < 50.
PublicResearchers used CLASS observations at four microwave frequencies to search for circular polarization—a twisting pattern in light’s electric field—in the cosmic microwave background. They found no statistically significant signal, but tightened the limits on how strong it could be by about fivefold on the largest angular scales studied and extended the search to smaller scales. Combining CLASS observations with Planck temperature measurements also produced the first limits on a possible relationship between temperature variations and circular polarization. That relationship is likewise consistent with zero. The study also examines circular polarization from Earth’s atmosphere, comparing its constraints with a model.
Young explorerScientists looked at microwave light from space for a special kind of twist. They used CLASS to look in more ways than before, but did not find a clear sign of the twist. That does not mean there is no twist at all—it could be too small to see. Their new work gives a tighter limit on how big it could be. They also checked whether warmer and cooler patches of this light went along with the twist, and found no clear sign of that either.
Robin Y. Wen, Lukas Tobias Hergt, Niayesh Afshordi+1 more
AstronomerCombined BAO and CMB data mildly favor departures from ΛCDM. The authors report that a one-parameter cosmic-glitch model, in which the cosmological gravitational coupling differs from Newton's constant as in Hořava gravity, fits at least as well as two-parameter dynamical dark energy. Planck+ACT+SPT and DESI DR2 yield G_cosmo/G_N = 0.9920 ± 0.0025, a 3.3σ preference for weaker cosmological gravity that persists when CMB lensing and supernovae are included. When fitted to CMB data alone, the glitch model predicts DESI distances, whereas w0waCDM does not. These findings favor, but do not establish, a departure from standard cosmology.
PublicMeasurements of the universe's ancient light and large-scale structure are showing a modest preference for something beyond the standard cosmological model. Rather than changing how dark energy evolves, this study considers a model with one adjustable parameter that makes gravity slightly weaker on cosmological scales than the strength described by Newton's constant. It fits the combined data at least as well as a dark-energy model with two adjustable parameters. The inferred difference is about 0.8%, with a statistical preference of 3.3 sigma—not a confirmed discovery. The preference persists when additional observations are included, and fitting the model only to the ancient-light data successfully predicts the DESI distances.
Young explorerGravity is the pull that helps hold things together. Scientists looked at very old light and patterns in where galaxies are. They tried an idea that gravity across the whole universe might be a tiny bit weaker than usual. The idea fits the clues well, and using just the old light, it also predicts distances that scientists measured. But the clues are not strong enough to say for sure that gravity really is different.
Kevin S. Croker, Joshua Cohon, Viktor T. Toth+13 more
AstronomerMotivated by interest following DESI Data Release 2, the authors construct a linear-order general-relativistic solution whose Hernandez-Misner-Sharp mass grows passively as a^κ. The constant κ appears in every eigenvalue of the Weyl and stress-tensor operators, identifying the growth as physical in both free-field and material sectors. The solution is causal over the spacetime relevant to stellar-collapse compact objects, and κ = 3 yields a cloud of energized vacuum, complementing previously predicted a^3 mass scaling for energized-vacuum black holes. This is a theoretical step toward exact κ ≈ 3 cosmologically coupled black-hole solutions and observational tests with pulsar binaries, not a demonstrated explanation of late-time acceleration; known models grow too slowly to drive it.
PublicCould black holes gain mass simply because the universe expands, and help explain why that expansion is speeding up? Existing models do not produce fast enough growth. This study develops an approximate solution to Einstein’s theory in which mass increases with cosmic expansion, and argues that the increase is physically meaningful rather than a mathematical artifact. A particular growth rate produces a cloud of energized vacuum in the model. The work is a theoretical first step toward more complete black-hole models that could be tested using pairs of objects containing pulsars; it does not report observations confirming this growth or its role in cosmic acceleration.
Young explorerSpace is getting bigger, and scientists wonder whether that could make black holes heavier. They made a math model in which mass grows as space grows. It is an early idea, not something they have seen happen. Later, they could check it by watching pairs of space objects that include a star sending out regular flashes.
Ibrahim Elsharkawy, Victoria Knapp-Perez, Wahid Bhimji+1 more
AstronomerThe authors present hAIthem, a computational framework for exploring testable beyond-Standard-Model signatures, demonstrated on a restricted set of single dark scalar multiplet models. Its reinforcement-learning agent is an autoregressive Large Lagrangian Model, pretrained on approximately one billion tokens from about 10,000 Lagrangians and fine-tuned through a Battleship-style interaction with phenomenology tools. It searches for parameter regions not excluded by selected subsets of constraints. A decision tree then separates these regions using computed observables, while competing LLM agents propose signatures for regions that remain degenerate. In this proof of concept, the RL search finds more viable and physically diverse regions than an evolutionary-algorithm baseline. Proposed signatures include applying a halo-independent kinematic ratio to paleo-detectors. These are computational search results and experimental suggestions, not detections of dark matter or demonstrations that the surviving regions satisfy every constraint.
PublicGravity provides strong evidence for dark matter, but it does not tell researchers which of many competing models is correct. The authors introduce hAIthem, an AI framework that searches theoretical possibilities and suggests ways to distinguish them experimentally. In a limited computational demonstration, its reinforcement-learning search found more varied possibilities consistent with selected constraints than a comparison search method. Other AI agents then proposed combinations of previously studied observables that might help separate similar models. The work suggests possible tests; it does not report a dark matter detection or establish that any model is correct.
Young explorerScientists have clues from gravity about mysterious matter, but they do not know exactly what it is. They made an AI helper that plays a searching game with possible explanations and suggests tests to tell them apart. The helper found ideas to explore, not the mysterious matter itself.
Damiano F. G. Fiorillo
AstronomerThis theoretical study examines singularities in neutrino flavor-wave dispersion relations when nonzero masses introduce a velocity spread. It distinguishes mode degeneracies from abrupt termination at branch cuts of the flavor dielectric function, deriving local expansions and conditions for both. Masses lift degeneracies along the symmetry axis, although degeneracy lines may remain elsewhere in three-dimensional wavevector space. Abrupt termination persists generically, with exceptions for special energy distributions that are entire functions. The authors also establish an exact equivalence between a collisionless plasma with a Lorentzian neutrino-frequency distribution and a monochromatic plasma with an effective collision rate, motivating sums of Lorentzians as a simplifying approximation for general distributions.
PublicNeutrinos can collectively change their type, or “flavor,” in wave-like patterns. This mathematical study asks how those waves change when neutrinos have mass and therefore a spread of speeds. It examines two behaviors: distinct wave modes merging and modes ending abruptly. Including mass removes the mergers along a symmetry axis, though mergers might still occur elsewhere; abrupt endings generally remain, except for special distributions of neutrino energies. The study also finds a mathematical shortcut: a particular spread of neutrino frequencies behaves exactly like a single-frequency model with an effective collision rate. This is a theoretical equivalence, not evidence that collisions actually occur.
Young explorerNeutrinos are tiny particles that can change from one kind into another. When many do this together, the changes can make waves. Scientists used math to study what happens when the particles travel at different speeds. Some waves that joined together in a simpler model no longer join in the same way, but waves can still stop suddenly. The scientists also found a shortcut that makes some of the wave math easier. They studied this with equations, not by watching the waves.
Juan P. Luengas, Maxim Pospelov, Harikrishnan Ramani
AstronomerThe authors analyze solar capture, energy loss, and annihilation of scalar and fermionic electroweak-multiplet dark matter, extending earlier Higgsino results. Sub-MeV mass splittings can permit large inelastic scattering cross sections. Doublets show somewhat distinct behavior, whereas higher representations behave self-similarly. For higher multiplets, the analysis of IceCube results constrains the splitting to approximately δ ≥ 350 keV for dark matter masses up to 100 TeV. Assuming thermal freeze-out and a Standard Halo Model velocity distribution, this excludes most electroweak dark matter models as explanations of LZ’s single reported high-recoil event. A high-velocity tail, such as one induced by the Large Magellanic Cloud, can instead move the LZ-preferred splitting above the solar bounds for many multiplets.
PublicThis study tests a family of hypothetical dark matter particles by calculating how they could be captured by the Sun, lose energy, and annihilate. Using IceCube results, the authors place limits on the mass difference between related particle states. Under specific assumptions about how dark matter formed and how fast it moves, these limits rule out most of the models studied as explanations for a single high-recoil event reported by the LZ collaboration—not as dark matter candidates altogether. The interpretation changes if the dark matter population includes more fast-moving particles, potentially because of the Large Magellanic Cloud: many of the models could then explain the event without violating the solar limits. The event is not established here as a dark matter detection.
Young explorerScientists are studying possible kinds of dark matter, invisible stuff in space. They worked out what might happen if the Sun caught some of its tiny particles, then compared their ideas with telescope results. Many of the ideas do not fit one unusual detector event if dark matter moves in the way they assumed. But if some particles move extra fast, more ideas might fit. This does not show that the unusual event really came from dark matter.
Dibash Plaban Kalita, Shreya Banerjee
AstronomerThis theoretical study examines primordial tensor perturbations in a Lorentz-violating Einstein-Æther-type inflationary framework with a non-canonical scalar kinetic term K_3X^2. For an analytically tractable, potential-free background, the authors derive the tensor propagation speed and examine effective couplings q_k = λ_Tφ_k^2 and q_k = λ_Tφ_k^4. The models yield distinct consistency relations between the tensor spectral index n_T and its running α_T, suggesting possible signatures in the primordial gravitational-wave spectrum. Derived constraints are compared with the late-time speed bound from GW170817/GRB170817A, but applying that bound to inflation requires an assumption about the intervening evolution of the tensor-sector coupling. These are theoretical predictions and constraints, not a detection of primordial Lorentz violation.
PublicThe researchers explore a theoretical model of the Universe's early rapid expansion in which gravitational waves can behave differently from what Lorentz symmetry normally allows. They calculate how the waves' speed and spectrum depend on the model's coupling, finding two different predicted relationships that could help distinguish such models. They also compare their work with the strong gravitational-wave speed limit inferred from GW170817/GRB170817A in the late Universe. That limit cannot automatically be applied to the early Universe: doing so requires assuming how the relevant coupling changed over cosmic history. The study offers a possible way to test these ideas, rather than evidence that Lorentz symmetry was broken.
Young explorerScientists used math to imagine tiny ripples in space when the Universe was very young and growing quickly. In their ideas, the ripples could move differently and leave different patterns. Those patterns might help scientists test the ideas someday. But a rule about how fast ripples travel today does not automatically tell us how fast they traveled long ago. This is a math study, not a discovery of those early ripples.
Giovani Dalla Valle Garcia, Juan Herrero-Garc\'ıa
AstronomerThe authors present a self-interacting dark-matter model comprising heavy dark baryons in a confining SU(N) sector with N approximately 10–100. Chromo-electric polarizability produces van der Waals interactions, yielding a predicted cross section per unit mass of roughly 30–100 cm²/g at dwarf-galaxy velocities, lower values compatible with galaxy-cluster requirements, and 100–1000 cm²/g at velocities of a few km/s. The low-velocity enhancement is motivated by the second perturber of JVAS B1938+666, rather than constituting a detection of dark baryons. For a specified heavy-constituent mass to dark-confinement-scale ratio, m_Q/Λ_d, the authors argue that astrophysical self-interaction constraints can infer N. The phenomenology favors GeV-scale dark baryons independently of relic-abundance considerations; at these masses, a dark baryon asymmetry comparable to the visible-sector asymmetry could account for the observed dark-matter abundance.
PublicThis theoretical study proposes that dark matter could consist of composite particles called dark baryons, whose interactions become stronger or weaker depending on how fast they move relative to one another. The model predicts strong interactions at the speeds typical of dwarf galaxies, weaker interactions at galaxy-cluster speeds, and especially strong interactions at very low speeds, as suggested by a perturber associated with JVAS B1938+666. These are model predictions, not a discovery of the proposed particles. Within the model, astronomical evidence could help determine the number of dark-sector “colors,” a property of the force binding the particles, provided a key mass-to-binding-scale ratio is specified. The preferred particle masses are around the GeV scale, where a dark-matter particle–antiparticle imbalance comparable to that of ordinary matter could explain the observed amount of dark matter.
Young explorerScientists are exploring an idea about dark matter, the invisible stuff in space. They imagine it is made of little bundles that push or pull on one another differently depending on how fast they move. Their calculations suggest the bundles could affect one another strongly when moving slowly and less strongly when moving fast. This might help explain clues from space, but scientists have not shown that these bundles really exist.
Giovani Dalla Valle Garcia, Juan Herrero-Garc\'ıa
AstronomerThis theoretical study models self-interacting dark matter as compact, Coulombic heavy baryons in a confining dark SU(N) gauge theory with one heavy vector-like quark and m_Q much larger than the confinement scale. Adapting the quarkonium operator-product expansion to heavy baryons, the authors derive leading interactions comprising non-retarded London dispersion, retarded Casimir-Polder forces, and Yukawa contributions from dark glueball exchange. Within the minimal setup, attraction cannot overcome short-distance Pauli repulsion for N=2 or 3, preventing phenomenologically relevant velocity dependence. At sufficiently large N, attraction can compete with the repulsive core. A representative SU(10) model has parameter regions compatible with self-interaction requirements inferred from dwarf galaxies and clusters, while permitting much larger low-velocity cross sections relevant to gravothermal evolution. These regions involve GeV-scale dark baryons and a confinement scale near that of QCD, motivating—but not establishing—an asymmetric dark matter origin.
PublicThe researchers explore a theoretical possibility: dark matter could consist of tightly bound particles whose interactions change with their relative speed. Their calculations include both attraction between these particles and repulsion when they get very close. In the simplest versions examined, repulsion prevents the strong speed dependence they seek. In a version with a larger number of internal particle types called colors, the calculated interactions can meet requirements inferred from dwarf galaxies and galaxy clusters, while becoming much stronger at low speeds. This could matter for how dark matter redistributes energy within galaxies. The study identifies promising properties for hypothetical dark matter particles; it does not detect them or establish that this model describes real dark matter.
Young explorerScientists are trying to understand dark matter, something in space we cannot see directly. They tried a mathematical idea in which tiny dark matter bundles can pull toward each other but push apart when they get too close. Some versions did not give the behavior they wanted. Another version could let slow-moving bundles affect each other much more strongly and could fit clues from galaxies. This is an idea worked out with math, not a discovery of those tiny bundles.
Pierce Giffin, Pankaj Munbodh, Elisa G. M. Ferreira
AstronomerThis theoretical study examines Bose-enhanced gravitational capture of ultralight axions into solar-bound gravitational atom states. Capture becomes exponentially efficient for axion masses of approximately 10^-14–10^-13 eV. For a representative decay constant of about 3.5 × 10^7 GeV, the calculations predict that the axion dark matter density at Earth can exceed ten times the standard Galactic value of 0.4 GeV/cm³. Assuming this overdensity, the authors derive updated axion-photon coupling limits from existing satellite and terrestrial measurements and improved sensitivity projections for upcoming experiments. The overdensity is a theoretical prediction, not a reported detection.
PublicThe Sun’s gravity could collect hypothetical dark matter particles called ultralight axions, increasing their density near Earth. The study calculates that, for particular particle properties, this density could become more than ten times the usual Galactic dark matter density. Using that predicted increase, the authors reinterpret existing satellite and ground-based measurements to update limits on how strongly axions interact with light. They also forecast improved prospects for future experiments. The work does not report finding axions or measuring the proposed buildup.
Young explorerScientists wonder if tiny invisible particles called axions could gather around the Sun because of its gravity. Their math says that, if these particles have the right properties, there could be many more of them near Earth than usual. They use this idea to help work out what experiments might find. Nobody has found these particles in this study.
Subhojit Roy, Pedro Schwaller, Carlos E. M. Wagner
AstronomerThe authors explore two supersymmetric interpretations of LZ’s reported nuclear-recoil candidate at approximately 248 keV, rather than establishing its origin. Elastic scattering involves a bino- or singlino-like neutralino with a diagonal axial Z coupling controlled by the Higgsino asymmetry X, not the total Higgsino fraction. Noncoincident spin-dependent and spin-independent blind spots allow suppressed Higgs-mediated scattering while retaining X around 0.01. The favored low tan beta creates Higgs-mass tension in the MSSM for few-TeV squarks, relieved by the NMSSM tree-level quartic. An NMSSM benchmark with neutralino mass approximately 500 GeV and X approximately 0.007 lies below current LZ limits and obtains its relic abundance through a singlet-like pseudoscalar resonance just above threshold, suppressing present-day annihilation. Alternatively, endothermic scattering of a pseudo-Dirac Higgsino requires a splitting of a few hundred keV, generated by PeV-scale gauginos, potentially lower-scale opposite-sign bino-wino cancellation, or weak singlino mixing. Solar-neutrino searches strongly constrain the minimal thermal inelastic realization. The mechanisms predict different recoil spectra beyond the candidate event.
PublicLZ has reported a possible nuclear recoil with an energy of about 248 keV. This study asks whether either of two proposed supersymmetric dark-matter mechanisms could explain it; the event is not established as a dark-matter detection. In one mechanism, a particle scatters without changing into a heavier state, with its interactions arranged to weaken some experimental signals while preserving others. The authors present a specific model example compatible with current LZ limits that also accounts for the particle’s relic abundance. In the other mechanism, the particle absorbs energy to change into a slightly heavier state during scattering. Searches for neutrinos from the Sun strongly constrain the simplest thermal version of that scenario. The two explanations predict different patterns of recoil energies beyond the reported candidate.
Young explorerA detector reported a possible bump to the middle of an atom. Scientists explored two ideas for how an unseen particle might make that bump: it could bounce, or it could become a little heavier as it hits. Neither idea is proven. They predict different patterns of bumps.
Euclid Collaboration, V. Duret, S. Escoffier+97 more
AstronomerThis study tests photometric BAO inference using the Flagship mock galaxy catalogue, rather than observed Euclid survey data. The authors measure angular two-point correlation functions in 13 redshift bins spanning 0.2 < z < 2.5 and fit templates to extract transverse Alcock-Paczynski dilation parameters. A joint MCMC and profile-likelihood analysis at effective redshift 0.77 yields D_A/r_d = 10.764 (+0.0839, −0.0849), a three-fold improvement over current Dark Energy Survey constraints in this mock-based analysis. Separate bin fits provide weaker distance constraints but enable cosmological inference, giving Ω_m = 0.296 (+0.074, −0.059) and h r_d = 99.35 (+4.29, −4.55) Mpc. The study also quantifies sensitivity to templates, scale cuts, redshift binning, and redshift-space distortions.
PublicEuclid is expected to observe about 1.5 billion galaxies, offering a way to trace the Universe’s expansion through a characteristic spacing pattern in galaxy clustering called baryon acoustic oscillations. Here, researchers tested that approach on a simulated galaxy catalogue, not on actual Euclid observations. They divided the mock galaxies into 13 distance-related groups and measured the pattern’s apparent angular size. Combining the groups produced a distance constraint about three times tighter than current Dark Energy Survey constraints; analyzing the groups separately also constrained the Universe’s matter content and a combination of its expansion rate and the pattern’s reference scale. The researchers checked how analysis choices and effects that alter apparent galaxy positions influence these estimates. These are simulation-based results, not a demonstrated precision from Euclid data.
Young explorerGalaxies make a pattern in space that scientists can use like a ruler. The Euclid survey is expected to see lots of galaxies, so scientists practiced using this ruler with a pretend galaxy map made on a computer. They split the pretend galaxies into 13 groups and studied the pattern to learn how the Universe grows. Using all the groups together gave a more precise answer than using each group alone. They also checked whether different ways of doing the work changed the answers. This was practice with a computer map, not a result from real Euclid pictures.
Kerstin E. Kunze
AstronomerThis modeling study calculates multifrequency angular power spectra of the redshifted neutral-hydrogen 21 cm signal in cosmologies containing both the adiabatic primordial curvature mode and a compensated magnetic mode. Primordial magnetic fields enhance the linear matter power spectrum on small scales, where their contribution can dominate the adiabatic contribution. Temperature maps are simulated for illustrative field parameters B0 = 4 nG and nB = -2.9 or -2.5. Cross-frequency spectra are calculated over frequency ranges centered on those of uGMRT Band 3 and MeerKAT L-band data, and signal-to-noise ratios are estimated for these instruments and SKA1-MID using system noise alone. The simplified calculations suggest potential for constraining primordial magnetic-field parameters, particularly with SKA1-MID, but foregrounds are omitted and no observational detection is reported.
PublicThe researchers explore whether radio signals from neutral hydrogen could reveal magnetic fields present in the early universe. Comparing simulated maps at different radio frequencies, which correspond to different cosmic redshifts, could help identify how these fields change the distribution of matter on small scales. The study tests two example magnetic-field models and estimates how well uGMRT, MeerKAT and SKA1-MID could measure the resulting patterns. The calculations look promising, especially for SKA1-MID, but they include only instrument system noise and leave out foreground radio emission. This is a simulation-based assessment, not a detection of ancient magnetic fields.
Young explorerHydrogen in space sends out radio signals. Scientists made pretend maps of those signals to see whether they could give clues about magnetic fields from when the universe was very young. Comparing maps made at different radio frequencies might help. Their test looks hopeful for a telescope called SKA1-MID, but they left out other radio signals that could get in the way. They have not found these ancient magnetic fields with this test.
Qi Chen, Yuan Yin
AstronomerThis theoretical study considers heavy-particle production during inflation from a transient quadratic U(1)-breaking interaction of a complex scalar derivatively coupled to the inflaton. The rolling inflaton generates an effective chemical potential, and sufficiently strong symmetry breaking produces a tachyonic instability. Its finite duration limits fluctuation growth while allowing efficient production of particles heavier than the Hubble scale with small homogeneous backreaction in some regimes. The authors calculate a peaked gravitational-wave spectrum by tracking the full time evolution of the fluctuations’ anisotropic stress. Idealized forecasts suggest possible LISA observability for suitable parameters and production times, contingent on the assumed switching profile and reheating history.
PublicThe researchers explore a theoretical way to create very heavy particles during the universe’s early period of rapid expansion, called inflation. A brief interaction can strongly amplify fluctuations in a particle field, while its limited duration keeps their growth in check. The calculations predict that these fluctuations would generate gravitational waves concentrated around a particular frequency. Under suitable assumptions, the proposed LISA observatory might detect the signal, but this is a forecast rather than an observation, and it depends on how the interaction turns on and off and how the universe reheats after inflation.
Young explorerWhen the universe was very young, it grew very fast. Scientists used math to explore whether a short burst of activity could make tiny, heavy particles and ripples in space. A detector called LISA might someday notice those ripples, but nobody has seen this signal yet. Whether it could be spotted depends on how the burst happened and what the universe did afterward.
Maria C. Straight, Tanvi Karwal, José Luis Bernal+1 more
AstronomerUsing Planck 2018 cosmic microwave background anisotropy data, the authors derive frequentist profile-likelihood constraints on velocity-independent dark matter–proton scattering, allowing only a fraction of dark matter to interact. They show that Bayesian posteriors suffer from prior-volume effects: as either the scattering cross section or interacting fraction approaches zero, other interaction-model parameters become unconstrained, favoring those regions of parameter space. Compared with the prior-independent profile-likelihood analysis, Bayesian inference consistently overestimates the constraints on the cross section. The authors recommend supplementing Bayesian limits with frequentist analyses to assess sensitivity to priors; this is a constraints analysis, not a detection of scattering.
PublicThe researchers used Planck measurements of the universe’s oldest light to assess how much dark matter could scatter off protons, including scenarios where only some dark matter interacts this way. They found that assumptions built into a commonly used statistical method can make the scattering appear more tightly constrained than an alternative analysis does. This happens because, when interactions become very weak or involve very little dark matter, the data no longer restrict some of the model’s other parameters. The study does not report finding these interactions. Instead, it recommends comparing statistical methods to check how much the inferred limits depend on prior assumptions.
Young explorerScientists studied very old light from space to see how much invisible dark matter might bump into tiny bits of ordinary matter. They did not find that these bumps happen. They found that one way of checking the clues can make the rules about possible bumps seem stricter than another way does. They suggest checking both ways so the answer does not depend too much on the assumptions they start with.
Sohini Dutta, Philip Bull, Jacob Burba+3 more
AstronomerThe authors extend the hydra-pspec Gibbs sampler to jointly infer the 21cm signal, its power spectrum, foregrounds, and multiplicative systematics in delay–fringe-rate space. The model addresses cable reflections, which place attenuated foreground copies outside the foreground wedge. Marginalising over the systematics avoids the additional signal loss associated with filtering them out. Tests on simulated single-baseline visibilities recover the 21cm delay power spectrum well across different systematic locations in delay–fringe-rate space; this is not a demonstration on observed data. The implementation is also suitable for modelling other multiplicative visibility effects, such as residual gain errors.
PublicDetecting the faint radio signal from the universe's reionisation era is difficult because much brighter radio emission and instrumental effects can obscure it. Reflections in telescope cables create faint copies of that bright emission in regions where researchers hope to isolate the early-universe signal. This study develops a statistical method that accounts for those reflections alongside the desired signal, rather than filtering them away and losing some of the signal too. In simulated data for one pair of antennas, the method recovered the signal's power spectrum well even when the reflections occupied different locations in the analysis. Its performance on real observations is not demonstrated here.
Young explorerScientists want to hear a very quiet radio message from the universe long ago, but louder messages get in the way. Telescope cables can make little echoes of those loud messages. The researchers made a computer method that accounts for the echoes instead of cutting them out and losing some of the quiet message too. It worked well in pretend telescope data from one pair of antennas, but this study did not show it working on real sky data.
Cian Roche, Mark Vogelsberger, Michael McDonald+9 more
AstronomerThe authors present a fully simulation-based procedure for cluster strong lensing that combines structure-preserving volume remapping with multi-plane ray tracing. Primary lenses, source galaxies, and all resolved intervening objects are drawn self-consistently from the simulated large-scale structure, avoiding some omissions and redshift-correlation losses of hybrid forecasts. Example light cones and images generated from IllustrisTNG provide a conservative assessment of line-of-sight effects. In these simulations, uncorrelated line-of-sight structure shifts relative image positions by several arcseconds and produces approximately 6% scatter in the primary critical-curve area. At source redshift z_s = 4, the reported change in total critical area within 100 arcseconds of the cluster potential minimum is 16%, with quoted uncertainties of +20% and -14%. These are simulation findings, not measurements from observed cluster lenses.
PublicA galaxy cluster can bend light from distant galaxies into multiple images. The authors developed a computer-simulation method that includes the cluster, distant galaxies, and other resolved objects along the light's path together, rather than assembling them separately. Their simulated examples show that intervening cosmic structure can shift the images and change the regions where strong lensing occurs. For example, unrelated structure along the viewing direction produces about 6% variation in one measure of the cluster's lensing area. The results demonstrate why matter along the full light path matters when predicting gravitational-lensing images; they are not new observations of real clusters.
Young explorerA big bunch of galaxies can bend light and make a faraway galaxy look like it has several pictures. Scientists made pretend galaxies in a computer and followed the light past them. In their computer pictures, other things along the way could move the pictures around and change where the strongest bending happens.
Rodrigo Fraga, Rafael C. Nunes
AstronomerThis forecasting study examines beyond-GR effects in the stochastic gravitational-wave background from unresolved binary black hole mergers, separating parametrized post-Einsteinian waveform-generation corrections from propagation effects encoded in a modified gravitational-wave luminosity distance. Injection-recovery analyses for Advanced LIGO, the Einstein Telescope, and Cosmic Explorer jointly vary gravity and population parameters, using a Power-Law plus Peak mass distribution and Madau–Dickinson merger-rate evolution. The forecasts indicate that frequency-dependent generation corrections distort the background spectrum and could be meaningfully constrained by third-generation detectors, particularly Cosmic Explorer. Propagation modifications mainly rescale the amplitude and are more strongly degenerate with population uncertainties. These are prospective constraints, not observed evidence of departures from GR.
PublicThe combined gravitational waves from many black hole mergers too faint to distinguish individually could offer a new way to test Einstein’s theory of gravity. This study uses simulations and detector forecasts to explore changes both in how those waves are produced and in how they travel across the universe, while allowing for uncertainty about the black hole population. Changes in wave production alter the background’s pattern across frequencies and may be testable with future detectors, especially Cosmic Explorer. Changes during travel mostly alter the overall signal strength, making them harder to separate from uncertainties about the mergers themselves. The study predicts future testing opportunities; it does not report a detected failure of Einstein’s theory.
Young explorerWhen black holes join together, they make ripples in space. Lots of faraway ripples can mix into one big background. Scientists used computer tests to ask whether future listening machines could find clues that gravity works differently than Einstein said. Changes in how the ripples are made might leave a special pattern. Changes as they travel could be harder to spot, because not knowing enough about the black holes can make the signal look similar. They have not found that gravity works differently.
Y. Nakato, W. L. K. Wu, Y. Omori+92 more
AstronomerThe authors construct CMB lensing B-mode templates using SPT-3G 2019–2020 E-mode and lensing-reconstruction data, supplemented by a Planck cosmic infrared background lensing tracer. They compare standard GMV, profile-hardened GMV, and polarization-only quadratic reconstructions, validating the templates with Gaussian and Agora simulations. In simulations, the profile-hardened GMV + CIB template suppresses foreground-induced power-spectrum bias to below 10% of its statistical uncertainty; data difference tests also show no evidence of significant foreground contamination. This template achieves average residual lensing BB power A_lens^res ≈ 0.48 over 20 ≤ ℓ ≤ 200, reported as the highest-efficiency delensing template to date. The method is intended for upcoming delensed BICEP searches for primordial gravitational-wave B modes, not a detection of those modes.
PublicGravity bends the light of the cosmic microwave background, creating a polarization pattern that can hide a similar signal from gravitational waves in the early universe. The researchers use SPT-3G and Planck observations to build a template of this unwanted lensing pattern. Simulations indicate that their preferred method strongly reduces bias from foreground emission, while tests of the real data find no evidence of significant foreground contamination. The template leaves about 48% of the original lensing polarization power, averaged over the range of angular scales studied, which the authors report as the best performance of such a template so far. It will be used in future BICEP analyses to improve searches for primordial gravitational waves; this work does not report finding them.
Young explorerScientists look at very old light from space for clues about tiny ripples from when the universe was young. But gravity bends that light and makes another pattern that can get in the way. The scientists made a map of the extra pattern so they can clean it away. Their tests suggest the map works well, though it does not remove everything. They plan to use it to help look for the tiny ripples, but they have not found them in this study.
Weiqiang Yang, Sibo Zhang, Dinorah Barbosa+3 more
AstronomerThe study constrains a dark matter–dark energy interaction model with Q = Γρ_x, where Γ is constant, considering vacuum-like (w_x = −1), phantom (w_x < −1), and quintessential (w_x > −1) dark energy. It uses Planck 2018 CMB, DESI DR2 BAO, and the PantheonPlus, Union3, and DES-Dovekie SNIa compilations. Combined CMB, BAO, and SNIa analyses support an interaction in the vacuum-like and phantom cases, but Bayesian model comparison still favors ΛCDM over those interacting models. The quintessential case yields mildly lower S_8 estimates across the datasets.
PublicResearchers tested whether dark matter and dark energy could exchange energy, comparing three versions of a model with observations of the early universe, galaxy clustering, and exploding stars. The combined data support an interaction in two versions, but a statistical comparison still favors the standard cosmological model, ΛCDM, over those alternatives. The third version gives slightly lower estimates of S_8, a measure related to how clumped matter is. These findings do not establish that dark matter and dark energy interact.
Young explorerScientists wondered whether two mysterious parts of the universe, called dark matter and dark energy, might pass energy between them. They checked three different ideas against clues from space. Two ideas showed hints that this could happen, but the usual explanation of the universe still did better in their comparison. The hints are not proof.
Bilal Tüdes, Luca Amendola
AstronomerThis study forecasts DESI and Euclid constraints on coupled dark energy using the one-loop galaxy power spectrum, examining sensitivity to the fiducial coupling, fixed potential slope, maximum wavenumber, and priors. Including mildly nonlinear scales improves the forecast coupling constraints by roughly a factor of five. The coupling distinguishable from zero at approximately 1σ is β = 0.15 for the reference case with k_max = 0.2 h/Mpc, falling to 0.05 in the most optimistic case with k_max = 0.3 h/Mpc and a Planck prior on Ω_m0. These are forecasts, not detections. Both thresholds exceed current constraints obtained under the assumption of constant coupling from at least decoupling to today; because this analysis uses only late-time data, the authors conclude that detectable models would need time-varying couplings.
PublicThe researchers estimate how well DESI and Euclid data could test a model in which dark energy is coupled to another component of the universe. Their forecasts suggest that including galaxy clustering on somewhat smaller, mildly nonlinear scales could improve limits on the coupling strength by about fivefold. A coupling of 0.15 could be distinguished from zero at the modest one-standard-deviation level in their reference setup; under the most optimistic assumptions, the threshold falls to 0.05. This is not evidence that such a coupling exists. Existing limits are tighter, but assume the coupling stayed constant over much of cosmic history. The authors argue that a coupling detectable using late-time data would therefore need to change over time.
Young explorerScientists want to see whether dark energy has a special connection to something else in the universe. They calculated how well maps of galaxies might help them look for it; they have not found it. Looking at more details in the maps could help, but a small connection would still be hard to spot. Their calculations suggest that a connection these maps could spot would need to change as the universe gets older.
Zhe Feng
AstronomerThis theoretical study examines slow-roll inflation in f(R, T, R_ab T^ab) gravity, where T is the energy-momentum trace and R and R_ab are the Ricci scalar and tensor. The authors derive the field equations in a spatially flat FLRW background with an inflaton as the matter source, retaining only the minimal curvature–inflaton coupling term. Under the slow-roll approximation, the resulting equations coincide with those of f(R, T) gravity containing an RT mixing term. Several inflaton potentials are explored through approximate analytical treatments and numerical calculations, with comparisons to existing observational data; the abstract does not state the outcome of those comparisons. An additional inflaton perturbation analysis neglects metric perturbations.
PublicThe researchers investigate a modified theory of gravity as a framework for inflation, the proposed period of rapid expansion in the early universe. They calculate how an inflation-driving field would behave when it is coupled to spacetime curvature. With a restricted coupling and an approximation in which the field changes slowly, their equations match those of another modified-gravity model. They examine several possible forms of the field’s potential energy using analytical approximations and numerical calculations, and compare the calculations with existing observations. The abstract does not say how well the models agree with the data. A separate analysis of small disturbances in the field leaves out disturbances in spacetime itself.
Young explorerScientists used math to study an idea about how the universe might have grown very quickly when it was young. They tried changing the rules of gravity and studying a slowly changing field that could help the universe grow. With some simplifying rules, their math looked the same as another gravity idea. They also compared their calculations with information about the universe, but this summary does not tell us whether the ideas matched well.
Ehsan Ebrahimian, Ali Akbar Abolhasani, Mehrdad Mirbabayi
AstronomerThis theoretical study examines primordial black hole formation from rare fluctuations during an early matter-dominated epoch. Flatter peaks have lower collapse thresholds but are rarer. For the extreme top-hat limit, previous work argued that velocity dispersion suppresses collapse unless ζ exceeds a threshold scaling as ζ_rms^(2/5). Accounting for the peak-shape distribution, the authors find a larger effective threshold, ζ_th ∼ ζ_rms^(1/10), for a realistic cosmic PBH abundance. The model requires ζ_rms ∼ 0.1, much larger than the observed fluctuation amplitude on CMB scales, making matter-era formation barely more efficient than radiation-era formation. The estimated dimensionless rms spin is a_rms ∼ ζ_rms^(7/4) ≪ 1, slightly higher than for radiation-era PBHs. These are model results, not detections of primordial black holes.
PublicThe researchers model how unusually dense regions in the early universe might have collapsed into primordial black holes during a period when matter dominated. The shape of each region matters: flatter regions can collapse more easily, but they are also less common. Including this trade-off raises the effective strength of fluctuations needed to produce a realistic abundance of these black holes. The model requires fluctuations much stronger than those observed on the scales measured by the cosmic microwave background. It therefore suggests that forming black holes in a matter-dominated period is only slightly easier than in a radiation-dominated period. The predicted black holes would spin slowly, though slightly faster than those formed during radiation domination. The study does not establish that primordial black holes exist.
Young explorerScientists used a model to ask whether extra-crowded places in the very young universe could squeeze into black holes. The shape of those places mattered: some shapes made squeezing easier, but those shapes were harder to find. Their model says making lots of black holes would still need very strong crowded spots. It also suggests these black holes would turn slowly. This is an idea tested with a model, not black holes the scientists have found.
Vincenzo Branchina, Riccardo Gandolfo, Arcangelo Pernace
AstronomerThis theoretical study proposes an infrared origin for the observed cosmological constant within an Einstein-Hilbert plus R² truncation of gravity. Across a wide region of parameter space, instabilities generate large-amplitude quantum fluctuations that dominate the renormalization-group flow. Once this regime is entered, the flow remains there toward the infrared and progressively loses sensitivity to its boundary conditions, approaching Λ_k ~ λ_IR k² with λ_IR = 1/[2(π − 2)]. Identifying the deepest infrared scale with the current Hubble scale, k_IR ~ H₀, yields Λ_IR ~ H₀². The claimed screening mechanism is a result of this truncated theoretical treatment, not a new observational measurement.
PublicThe cosmological constant describes a contribution to the universe’s expansion. This theoretical study suggests that its observed value could be controlled by the universe’s largest present-day scale rather than by microscopic contributions to vacuum energy. In an approximate model of gravity, strong quantum fluctuations make the calculated cosmological constant increasingly insensitive to the model’s starting conditions. Taking the final scale to be the current Hubble scale then gives the proposed size of the observed constant. This is a theoretical mechanism within a particular approximation, not an observational confirmation.
Young explorerScientists made a math model to explain a number that helps describe how the universe expands. In their model, tiny quantum wiggles in gravity become strong and make that number depend less on how the calculation started. They suggest that the biggest scale of today’s universe sets the number instead. This is an idea from a model, not something they have proved by watching the sky.
