Artem Basyrov
AstronomerAsymmetric telescope beams invalidate simple harmonic-space Bℓ factorisation and couple modes across ℓ and m. The authors develop a map-domain treatment that applies beam convolution as a local, scan-dependent operation directly to time-ordered data, accommodating the full beam shape and providing a direct handle on intensity-to-polarisation leakage. In a noiseless validation against spherical-harmonic convolution, the method reproduces the input temperature and B-mode power spectra up to ℓ ≃ 1000, beyond the range relevant to primordial B-mode science. This is a computational validation, not an observational result or a test under noisy conditions. The abstract also outlines, rather than demonstrates, a sparse linear BeamOperator implementation for modular map-making.
PublicA telescope’s response to light is not perfectly symmetric. This can mix patterns in a sky map and make some intensity signal appear as polarisation. The authors develop a computational method that accounts for the telescope’s full response and how it scans the sky, applying the calculation directly to the recorded data sequence. In a test without noise, the method reproduces the input temperature and B-mode polarisation patterns’ power spectra up to a stated angular-detail limit of about ℓ = 1000, beyond the range needed for primordial B-mode studies. The result validates the calculation in that idealised test; it does not establish performance with noisy observations. The authors also outline how to incorporate the method into modular sky-map software.
Young explorerA telescope can blur a picture of the sky more in one direction than another. That can mix up different kinds of light signals. The researchers made a new way to calculate this blur while keeping track of how the telescope moves across the sky. In a computer test with no extra noise, their method matched the test picture’s patterns over the range they checked. That is a useful check, but it does not yet show how well the method works with noisy telescope data. They also describe how it could become part of a program that makes sky maps.
Matteo Longo Minnolo, Matteo Billi, Giuseppe Puglisi
AstronomerThis study forecasts sensitivity to anisotropic cosmic birefringence (CB), which remains undetected despite strengthened Planck evidence for a nonzero isotropic rotation. Anisotropy could help distinguish a homogeneous quintessence-like field from spatially varying axion-like dark matter. The authors apply patch-based localization to simulated CMB-plus-white-noise maps with Simons Observatory SAT- and LiteBIRD-like sensitivities, reconstructing local rotation angles by minimizing a chi-squared EB statistic built from the EB D-estimator. Under these idealized assumptions, forecast angular-power-spectrum statistical uncertainties improve over current Planck-based constraints by factors of 26–40 for a satellite-like mission and 11–15 for a realistic ground-based footprint. Scale-invariant fits to reconstructed bandpowers yield forecast 95% confidence upper limits of A_CB < 3.5 × 10^-4 deg² and A_CB < 7.1 × 10^-4 deg², respectively, corresponding to approximately 20-fold and 10-fold improvements over the current full-sky Planck amplitude constraint. These are simulation-based forecasts, not detections, and represent upper bounds on achievable gains.
PublicCosmic birefringence is a possible rotation of the polarization of light from the cosmic microwave background. Recent Planck analyses have strengthened evidence for a rotation that is uniform across the sky, but a rotation that varies from place to place has not been detected. Such variation could help distinguish different kinds of hypothetical fields, including one associated with axion-like dark matter. The researchers tested a method for measuring rotation in separate sky patches using simulated maps with noise levels representative of forthcoming ground- and space-based experiments. Their forecasts suggest roughly 10-fold and 20-fold improvements, respectively, in limits on the strength of a particular model of this variation. These are optimistic estimates from idealized simulations, not measurements or guaranteed improvements.
Young explorerScientists study very old light from space to see whether the direction of its tiny wiggles has turned. There are clues that it may have turned the same way across the sky, but scientists have not found different turns in different places. They practiced with pretend sky maps to see how well future telescopes might look for those differences. The practice suggests better searches are possible, but real observations may not do as well.
Alex Alarcon, Carles Sánchez
AstronomerThe study identifies cancellation between positive and negative magnification responses as a source of suppressed foreground-background clustering cross-correlations in deep photometric samples. Using DES Year 6 photometry and Balrog synthetic-source injections, it explores background selections at z ≈ 0.7–2.5 split by response sign and amplitude. The proposed BigMag framework combines foreground clustering with cross-correlations using these response-selected backgrounds to reduce cancellation. Forecasts with DES-like simulated data vectors indicate that an optimistic sample configuration and sufficiently precise response calibration could deliver constraints comparable to traditional 2×2pt using positions alone. The selected samples also enhance inverse galaxy-galaxy lensing, a position-shear correlation dominated by magnification when the position sample lies behind the shape sample. Forecast combinations of BigMag and this correlation self-calibrate magnification responses and yield marginalized S8 constraints comparable to traditional 3×2pt, or tighter in the more precise calibration scenarios examined. Near-zero-response selections could also support traditional 3×2pt and geometric lensing-ratio analyses. These are forecast capabilities, not demonstrated cosmological constraints from the observational data; further selection optimization and validation are needed.
PublicGravity bends light from distant galaxies, changing how many of them appear in a selected sample. For some galaxy selections this magnification increases the counts, while for others it decreases them, so combining the two can partly erase the signal. Using DES Year 6 galaxy data and tests that insert artificial sources, the researchers explore separating distant galaxies according to how they respond. Their proposed method, BigMag, uses galaxy positions to measure the resulting relationships between foreground and background galaxies. Simulations suggest that, with an optimistic galaxy selection and accurately calibrated responses, it could constrain cosmology as well as a standard method that also measures galaxy shapes. Combining BigMag with a related position-and-shape measurement could further improve constraints on S8, a measure of matter clustering. These projected benefits still require further optimization and validation; they are not yet demonstrated measurements of cosmological precision.
Young explorerGravity can bend light from faraway galaxies. This can make more galaxies show up in one group and fewer show up in another. If we mix those groups, their clues can cancel out. The scientists explored sorting the galaxies so the clues are easier to see. Their computer tests suggest this could help us learn about the universe, but they still need to check carefully how well it works.
Elisa J. Gao, Dhayaa Anbajagane
AstronomerUsing the IllustrisTNG runs in CAMELS, the authors quantify the cosmological and astrophysical dependence of the mean, scatter, skewness, and kurtosis of halo concentration. Normalizing flows model the concentration distribution as a function of halo mass, redshift, and six cosmological/astrophysical parameters over M_vir = 10^11–10^14.5 solar masses/h and z = 0–1. In these simulations, all higher-order moments show mass-dependent sensitivity to cosmology and astrophysics. Dark matter-only behavior is consistent with known effects of active mergers and tidal stripping in smaller halos. With galaxy formation included, scatter becomes non-monotonic near the Milky Way mass scale, with its amplitude strongly affected by the baryon fraction and supernova feedback parameters. Skewness is highly sensitive to the baryon fraction but mostly insensitive to the other parameters, while kurtosis follows the skewness behavior. ASTRID simulations show similar trends. These simulation results matter for analyses requiring the full concentration distribution, particularly at or below the Milky Way halo mass scale.
PublicA halo’s concentration describes how matter is distributed within it. This study uses computer simulations, rather than observations, to examine not just the average concentration of halos of a given mass, but also how widely concentrations vary and how uneven or tail-heavy their distribution is. The simulations show that these features respond to both cosmology and the physics of galaxy formation, with different effects at different halo masses. When galaxy formation is included, the spread in concentrations varies non-monotonically around the mass scale of the Milky Way’s halo. The strength of this pattern depends strongly on the fraction of matter in ordinary matter and on feedback from supernova explosions. The distribution’s asymmetry is also particularly sensitive to the ordinary-matter fraction. A second simulation suite shows similar behavior. The findings indicate that studies relying on the full range of halo concentrations should account for these dependencies, especially for halos no more massive than the Milky Way’s.
Young explorerGalaxies sit inside big clouds of matter called halos. Some halos have more of their matter packed toward the middle than others. Scientists made computer versions of these halos to see how they differ. In their simulations, adding the things that happen when galaxies form changed the pattern of how tightly matter was packed, especially for halos around the size of our galaxy’s halo. The amount of ordinary matter and the effects of exploding stars helped change that pattern. These are clues from computer models, not things the scientists watched happen in real halos.
Jeremy Sakstein, Harry Desmond
AstronomerThe study tests proposed rapid changes in Newton’s gravitational constant, G, 73–130 million years ago as possible resolutions of the Hubble tension. Fully convective red dwarfs below approximately 0.35 solar masses have thermal timescales comparable to these look-back times and could retain a present-day radius signature. Comparing predicted radius changes with mass-radius measurements of eight red dwarfs in detached eclipsing binaries, the authors exclude the proposed 4% G step 73 million years ago at 3.1σ and the proposed 11% step 130 million years ago at 4.0σ. These constraints apply to the two specified G-step models, rather than establishing that G has never varied.
PublicCould a sudden change in gravity’s strength help explain the Hubble tension, a disagreement about how fast the universe expands? This study tests two proposed changes: 4% about 73 million years ago and 11% about 130 million years ago. Small red dwarf stars adjust slowly enough that their sizes could still carry signs of such changes. The researchers compared predicted sizes with measurements of eight red dwarfs in pairs whose stars eclipse each other. The observations rule out the two proposed models at statistical significances of 3.1 and 4.0 sigma, respectively. This does not rule out every possible change in gravity.
Young explorerScientists wondered whether gravity, the pull that holds things together, suddenly changed a very long time ago. Little red stars change their size slowly, so their sizes today might still show clues. Scientists worked out what two suggested changes in gravity would do, then checked the sizes of eight stars. The sizes did not fit those two ideas well. That does not mean gravity could never have changed in some other way.
Chris Clarkson, Roy Maartens
AstronomerThis theoretical study develops a covariant kinetic completion of cold-dark-matter dust cosmography without assuming a background spacetime or geometrical symmetry. Dust flow is geodesic and has no intrinsic local Hubble dipole, but its description fails at stream crossing. Starting from the exact massive Vlasov hierarchy, the authors construct energy-integrated moments ordered by velocity weight. A self-consistent quadrupole truncation closes the dynamics on energy density, isotropic pressure and anisotropic pressure. Pressure gradients generate matter-frame 4-acceleration; the authors obtain an exact nonlinear solution of the momentum constraint that remains valid without truncation, rather than prescribing an arbitrary acceleration. They also derive nonlinear vorticity evolution, with velocity dispersion sourcing vorticity through the acceleration's curl. In covariant local cosmography, this acceleration supplies the intrinsic Hubble dipole and contributes to deceleration multipoles. The framework identifies quantities needed to test collisionless matter with local distance–redshift data; it does not report an observational detection. A companion paper specialises the hierarchy to perturbed FLRW spacetime and predicts signal amplitudes.
PublicThis paper develops a theoretical description of cold dark matter when streams of particles cross. Treating dark matter as pressureless dust becomes inadequate in that situation, whereas a model allowing particles to have different velocities can handle it. The authors derive equations linking those velocity differences to pressure, acceleration of the collective matter flow and rotational motion. They then show how this acceleration enters the mathematical description of nearby cosmic expansion, producing an intrinsic directional component and affecting the description of how expansion changes. The framework does not assume a particular background geometry. It identifies what would need to be tested using nearby objects' distances and redshifts, but reports no observational detection. Predictions of signal sizes are left to a companion paper.
Young explorerImagine streams of invisible space matter crossing, with particles moving at different speeds. A very simple picture cannot describe this well, so scientists made a more careful set of equations. Their equations show how these motions could make nearby space's expansion look different in different directions. This is a math study, not a report that they have seen that effect in the sky.
Yu Zhou, Yun Wang, Haozhe Zhang+4 more
AstronomerUsing Fisher-matrix forecasts for halo catalogs from the Quijote and Quijote-PNG simulations, this study tests the redshift-space monopole power spectrum of the Zel'dovich-inspired (ZI) transformed halo density field. The local nonlinear transform can Gaussianize the late-time matter field and encode higher-order correlation information in its power spectrum, with eta controlling the weighting of that information. A joint statistic combining eta = 1, 10, and positive infinity forecasts substantially tighter constraints than the conventional halo monopole on standard cosmological parameters, summed neutrino mass, and primordial non-Gaussianity amplitudes, and outperforms the marked power spectrum for many parameters. A calibrated scale-dependent noise correction further improves the forecasts: relative to the conventional halo monopole, constraints on equilateral and orthogonal f_NL, M_nu, and n_s improve by factors of 5.6, 5.5, 5.2, and 5.8, respectively. These are simulation-based forecasts, not observational measurements, and suggest that ZI power spectra could complement standard two-point statistics. The forecasts may be conservative because the simulated halo catalogs have substantially lower number densities than expected for forthcoming galaxy surveys.
PublicResearchers tested a way to extract more information from the pattern of matter in the universe using simulated catalogs of dark matter halos. Their method reshapes the density map so that its power spectrum—a measure of clustering—can capture information from more complex patterns that a conventional power spectrum does not capture. Combining three versions of this transformation gave tighter predicted limits on cosmological parameters, including the total mass of neutrinos and possible departures from Gaussian patterns in the early universe. Correcting for noise that varies with scale improved the predictions further; for four highlighted parameters, the predicted limits were tighter by factors of about five to six compared with the conventional halo power spectrum. These findings come from simulations and statistical forecasts, not measurements of the real universe. The method could complement existing clustering analyses, and its forecasts may be conservative because future galaxy surveys are expected to sample objects more densely than the simulated catalogs used here.
Young explorerScientists used computer-made universes to try a new way of studying where matter gathers in clumps. They changed the maps in three different ways and studied them together to find more clues in the patterns. In their computer tests, this helped them predict how closely they might learn some things about the universe, including how much tiny particles called neutrinos weigh altogether. Accounting for noise in the maps helped too. They have not shown this with real sky measurements yet, but the method might help scientists learn more from future maps of galaxies.
Yupeng Zhang, Shuxun Tian, Zhengxiang Li
AstronomerThis study forecasts a spectroscopic probe of the moving-lens effect, in which transverse motion of a gravitational potential shifts photon frequencies. Complementing recently reported statistical evidence from CMB–large-scale-structure cross-correlations, it considers differential redshifts between widely separated images of the lensed quasar SDSS J1004+4112. Monte Carlo forecasts combine information across the C IV and C III] broad-line profiles for an ELT-like configuration and include photon noise only. Assuming a lens transverse velocity of 500 km/s and an orientation that maximizes the signal, the expected moving-lens differential redshift is about 6.7 × 10⁻⁷ in magnitude. A 40-hour integration yields a forecast joint uncertainty of about 2.5 × 10⁻⁷, with C IV providing most of the constraint and C III] adding modest improvement. These are sensitivity forecasts, not a detection: photon statistics can reach the characteristic signal scale, but practical detectability depends on controlling astrophysical and instrumental systematics.
PublicA gravitational lens moving sideways can slightly change the frequencies of light passing through it. Researchers explore whether this effect could be measured by comparing the spectra of different images of the same distant quasar, SDSS J1004+4112, whose light takes different paths through a foreground lens. Their computer forecasts use two broad emission lines and an ELT-like telescope setup. With an assumed sideways lens speed of 500 km/s and the most favorable direction of motion, the predicted difference in redshift is about 6.7 × 10⁻⁷. For 40 hours of observing, the forecast uncertainty from photon noise alone is about 2.5 × 10⁻⁷. One line, C IV, supplies most of the sensitivity. The study does not report a detection with this method: it shows that enough photons could be collected to approach the signal’s scale, while effects from the astronomical source and the instrument remain practical challenges.
Young explorerGravity can bend light from a faraway bright object so that we see it in several places. If the thing bending the light moves sideways, it can also change the light’s color by a tiny amount. Scientists used computer tests to ask whether a big telescope could spot that tiny difference between the pictures. The tests suggest that collecting light for many hours might help, but they only counted one kind of fuzziness in the measurement. Other things in space and in the telescope could make it harder. They have not spotted this tiny change with this method yet.
Gabriel P. Lynch, Jens Chluba, Richard Battye+1 more
AstronomerThe authors constrain unresolved, small-scale electron density fluctuations by implementing two effects in the modified Boltzmann code classito: accelerated recombination and a reduction in effective Thomson scattering from line-of-sight correlations, which enhances diffusion damping increasingly with coherence length. Using Planck, ACT DR6, and SPT-3G D1 data, they report the first limits incorporating this modified photon transport and find no evidence for the fluctuations. The electron density contrast variance is below 0.21 at 95% confidence, tightening to 0.033 for a coherence length of 2 Mpc; limits are also expressed in terms of the electron power spectrum over approximately 1–100 Mpc^-1. As a proposed resolution of the Hubble tension, the fluctuations fare differently across datasets. In Planck, partial degeneracy between transport and accelerated recombination broadens the allowed H0 range; with a distance-ladder prior, H0 = 71.1 ± 0.7 km s^-1 Mpc^-1 and the fit improves relative to LCDM. ACT and SPT-3G break that degeneracy chiefly through damping-tail temperature–E-mode correlations; with the same prior, they give H0 = 69.3 ± 0.5 km s^-1 Mpc^-1 and no preference over LCDM. The publicly available implementation enables tests of models through their predicted fluctuation variance and coherence length.
PublicThis study tests whether tiny variations in electron density in the early universe could have changed the cosmic microwave background, the light left over from that era. The researchers modeled two effects: the variations would speed up the process by which electrons joined atoms, and correlated variations along light’s path would reduce effective scattering, making small-scale patterns in that light more strongly smoothed. Comparing the model with Planck, ACT, and SPT-3G observations, they found no evidence for these variations and set upper limits on their strength. The limits become tighter when the variations remain correlated across larger distances. The team also revisited the idea that these variations might explain the disagreement over the universe’s expansion rate. Planck data combined with a distance-ladder prior allowed a higher expansion rate and a better fit than the standard LCDM model. But ACT and SPT-3G data, using the same prior, favored a lower rate and showed no preference for the proposed explanation over LCDM. The findings therefore limit, rather than establish, this possible solution.
Young explorerLong ago, the universe had light and tiny particles called electrons. Scientists wondered whether some places had more electrons than others, making little clumps. They worked out how those clumps could change the old light we can still study today. When they compared their model with observations, they found no sign of the clumps, though very small ones could still be hiding. They also checked whether clumps could help explain why different ways of measuring how fast the universe grows give different answers. One set of observations made the idea look helpful, but the other sets did not. So the clumps are still an idea, not something scientists have found.
I. Y. Park
AstronomerThe study tests two finite-temperature quantum-gravitational corrections to the cosmological constant, parameterized by ΩΛ2 and ΩΛ3, whose associated density terms scale as a⁻⁴ and a⁻², respectively. Extending earlier machine-learning best-fit analyses, the authors use Bayesian MCMC with modified CLASS and Planck 2018 likelihoods to obtain marginalized constraints. Both parameters are consistent with zero, and ΩΛ3 is constrained only from one side. A separate CMB pipeline based on Weinberg’s kinetic-theory formulation and validated against CLASS is used for theoretical response analysis. It finds that the ΩΛ3 response is almost entirely absorbed by a shift in h across well-measured acoustic multipoles; the remaining signal lies at low ℓ, where cosmic variance dominates. The ΩΛ2 response is nearly degenerate with the spectrum’s overall amplitude. The authors attribute the weak constraints and lack of detection to these degeneracies and to the small CMB effects of the higher-order thermal corrections.
PublicThe researchers tested a model in which temperature-related quantum-gravity effects add two small corrections to the cosmological constant. They compared the model with Planck 2018 measurements of the cosmic microwave background, accounting for uncertainty in the model’s parameters. Neither correction was detected: both remain compatible with zero, and one is bounded only on one side. To understand why, they also built a separate calculation of the microwave background and checked it against an established code. Their calculations show that one correction mostly mimics a change in the cosmic expansion parameter h, while the other nearly mimics a change in the overall strength of the background’s pattern. The distinctive part of the first correction appears mainly on large angular scales, where cosmic variance limits what the data can establish. Thus, these data provide only weak constraints rather than evidence for the proposed corrections.
Young explorerScientists looked at an old glow from space to check an idea about two tiny changes in how the universe works. They did not find a clear sign of either change, but that does not prove the changes are absent. Their calculations showed that the tiny changes could look almost like other changes in the glow, making them hard to tell apart. The part that might look different is also hard to judge from the sky we can see.
Nobuhiro Okabe
AstronomerThe authors develop a Bayesian framework for cluster mass–concentration relations that incorporates intrinsic concentration scatter, nonlinear weak-lensing calibration, measurement-error covariance, and parent mass distributions, using Hamiltonian Monte Carlo for inference. They analyze 213 X-ray-selected clusters with weak-lensing measurements from eRASS1, XXL, LoCuSS, and MCXC at 0 < z < 0.9, accounting for subsample-specific calibration and population distributions. They compare a single power law, an empirical double power law, and four simulation-calibrated theoretical models. The sample does not reach the mass and redshift regime of the simulation-predicted high-mass upturn, so discrimination rests mainly on curvature. All inferred relations agree well with recent simulations, and no model differences exceed 4σ significance. A monotonically decreasing, positive-curvature relation is modestly preferred: at 2σ over the single power law and negative-curvature decreasing model, and at 0.5–1σ over three double-power-law models. This suggests gradual flattening at higher masses, not detection of an upturn.
PublicThis study examines how the concentration of galaxy clusters—how centrally packed their mass is—changes with cluster mass. The researchers developed a statistical method that accounts for measurement uncertainties, natural variation among clusters, and differences between the surveyed populations. Using 213 X-ray-selected clusters with weak-lensing measurements, they compared six possible descriptions of the mass–concentration relationship. All gave results consistent with recent computer simulations. The data mildly favor a pattern in which concentration decreases as mass increases, but the decline becomes gentler for more massive clusters. That preference is not decisive: it reaches 2σ against two alternatives and is weaker against the others, with no differences exceeding 4σ significance. Some simulations predict that concentration eventually rises again at very high masses, but this sample does not cover the range needed to test that predicted upturn.
Young explorerScientists studied 213 huge groups of galaxies to ask how tightly their matter is packed near the middle. They compared different ideas with measurements. The clues slightly favor an idea where heavier groups are less tightly packed, but that change gets smaller as groups get heavier. The clues are not strong enough to choose for sure. Computer models predict another change for some very heavy groups, but these measurements cannot test that yet.
Yukang Zhang, Pengjie Zhang
AstronomerThe study tests whether a cosmological constant with weak violations of the cosmological principle, modeled using ΛLTB cosmology, can mimic dynamical dark energy inferred under an FRW description. DESI DR2 BAO and Planck CMB data, combined with any of UNION3, Pantheon+, DES SN5YR, or DES Dovekie SNe Ia, do not favor either explanation over the other. Adding kinematic Sunyaev–Zel’dovich constraints excludes much of the cosmological-principle-violation parameter space allowed by those combinations. Nevertheless, a region of approximately 300 Mpc/h with roughly 10% excess matter density remains allowed, not established as a detection, and provides a viable alternative to dynamical dark energy. The authors also present analytical distance–redshift and kSZ expressions for further tests of weak cosmological-principle violation.
PublicRecent evidence that dark energy may change over time could instead reflect a universe whose matter is not distributed quite as uniformly as usually assumed. The researchers tested a model with constant dark energy and a modest departure from that uniformity. Combining measurements from DESI, Planck, and four alternative supernova compilations did not favor this model over changing dark energy, or vice versa. An additional test using the kinematic Sunyaev–Zel’dovich effect ruled out many of the nonuniform possibilities. Current data still permit a region about 300 Mpc/h across in characteristic scale with roughly 10% more matter than average; this is an allowed possibility, not a detected region. The study supplies mathematical expressions to help test the alternative further.
Young explorerScientists are checking whether dark energy changes over time or stays the same. If matter is spread a little unevenly through the universe, dark energy that stays the same might look as if it is changing. The scientists compared these ideas with measurements, but neither idea clearly won. Another check ruled out many uneven patterns, though a big patch with a little extra matter could still fit. They have not shown that this patch really exists.
Ryota Himeno, Atsushi J. Nishizawa, Kiyotomo Ichiki
AstronomerThis study tests whether primordial CMB B-mode polarization improves discrimination between a cubic three-torus (E₁) topology and trivial topology. The authors construct full harmonic-space covariance matrices for temperature, E-mode, and primordial B-mode anisotropies, retaining topology-induced correlations between distinct (ℓ,m) modes. They evaluate Gaussian likelihoods on random realizations of statistically isotropic ΛCDM with trivial topology, rather than on observed CMB data. In an ideal cosmic-variance-limited setting that neglects instrumental noise and gravitational lensing, adding primordial B modes provides only marginal improvement in distinguishing E₁ from trivial topology. The authors interpret the differing constraining power of the three observables through their transfer-function responses and topology-induced off-diagonal correlations.
PublicCould space connect back on itself rather than have the simple global structure usually assumed in cosmology? The researchers investigated one such possibility: a cubic three-torus, in which opposite faces of a cube are identified. This structure could create distinctive correlations in the cosmic microwave background, the universe’s ancient background light. Using simulated skies, they tested whether adding a polarization pattern called primordial B modes would help distinguish this topology from the standard assumption. It helped only marginally, even in an idealized analysis without instrument noise or gravitational lensing. This is a simulation-based finding, not an observational detection of the universe’s shape.
Young explorerImagine a universe where going far enough in one direction could bring you back to where you started. Scientists made pretend maps of the universe’s very old light to test one version of that idea. They checked whether adding another kind of pattern in the light would make the idea easier to spot. It helped only a little, even when they left out some things that make real maps harder to study. They have not shown that our universe really loops around.
Athanasia Gkogkou, Victor Bonjean, Jean-Luc Starck+3 more
AstronomerJESSNet is a beam-aware, mask-compatible foreground-cleaning framework for single-dish H I 21 cm intensity mapping, extending SDecGMCA with multiscale angular decomposition, scale-dependent mixing matrices and channel selection, learned spherical-wavelet sparse regularization, and mask-constrained reconstruction. It is tested on simulated SKA-MID-like observations spanning 900–1300 MHz (z ≈ 0.09–0.58), including H I emission, Galactic and extragalactic foregrounds, thermal noise, and an oscillating MeerKAT-inspired chromatic beam. In these simulations, it accurately recovers the input H I angular and frequency power spectra, improves recovery at low and intermediate angular scales compared with a single-scale implementation, and reduces residual beam-induced spectral features. Tests with a synthetic survey footprint also preserve the H I power spectra under incomplete sky coverage. These are simulation results, not a demonstration on observational data; the code and analysis pipeline are publicly released.
PublicRadio maps of neutral hydrogen can help astronomers study the universe, but other radio emission can obscure the hydrogen signal. A telescope’s response also changes with frequency, complicating the separation, and surveys may cover only part of the sky. The researchers introduce JESSNet, software designed to address these problems by analyzing sky structure at multiple scales, using a learned mathematical filter, and accounting for gaps in coverage. In simulated observations resembling those expected from SKA-MID, JESSNet recovered the statistical patterns of the hydrogen signal more accurately than a single-scale version in some ranges and reduced unwanted features caused by the telescope response. It also worked with a simulated partial-sky survey. The software is publicly available, but the abstract reports tests on simulations rather than real observations.
Young explorerImagine trying to hear a quiet sound while lots of louder sounds play around it. Astronomers have a similar problem when they look for radio signals from hydrogen in space. They made a computer helper called JESSNet to separate those signals from unwanted ones, even when parts of the sky picture are missing. They tested it on pretend sky pictures made by a computer, and it did a good job of finding the patterns in the hydrogen signal. That is promising, but these tests were not done with real sky observations.
Shin'ichiro Ando
AstronomerThe authors present a resolution-free, semi-analytic SMBH-binary gravitational-wave background calculation that directly integrates an N-body-recalibrated extended Press–Schechter accretion kernel, avoiding Monte Carlo merger trees, emulators, and precomputed model banks. Their continuous coupling of simulation-calibrated satellite tidal stripping to Chandrasekhar dynamical friction predicts stalling below a nearly redshift-independent mass ratio of ξ ≃ 0.04, with 38% of accreted satellites remaining unmerged at z = 0. Including per-binary stellar-hardening turnovers and eccentric spectra, they fit a five-parameter posterior to the NANOGrav 15-year Hellings–Downs-correlated free spectrum. They exclude the 15.8 nHz bin because a subsequent chromatic-noise reanalysis attributes its excess power to pulsar noise. The fit favors a black-hole mass normalization 0.31 dex above the locally calibrated black-hole–bulge relation, with reported uncertainties of +0.20 and −0.23 dex. This preference is reported as robust to the tested delay models, merger kernels, local mass calibrations, and redshift evolution. Eccentric binaries and dense stellar environments remain compatible with the spectrum but are not required.
PublicThis study develops a fast model of the combined gravitational waves produced by pairs of supermassive black holes and compares it with NANOGrav’s 15-year pulsar-timing data. In the model, small satellite systems can lose mass faster than they move inward, preventing them from merging: 38% of accreted satellites remain unmerged by the present day. That percentage is a model prediction, not a direct observation. The data favor a higher black-hole mass scale than the locally calibrated relationship between black-hole mass and a galaxy’s central bulge would suggest, although the estimate remains uncertain. The researchers leave out one frequency bin whose excess signal was attributed to pulsar noise in a later reanalysis. The measured spectrum allows black-hole pairs with elongated orbits or dense surrounding stars, but does not establish that either is necessary.
Young explorerTwo huge black holes moving around each other can make tiny ripples in space. Scientists made a computer model of many such pairs and checked it using the timing of flashing stars called pulsars. Their model says some small systems get stuck before they can join bigger ones. The pulsar data favor heavier black holes than a nearby-galaxy rule would suggest, but scientists are still unsure exactly how heavy they are.
Leila Ohashi, Sayan Saha, Jacqueline E. McCleary
AstronomerThe study benchmarks red-sequence-based cluster-member identification using SuperBIT multiband imaging from its April 2023 science flight. Spectroscopically identified members provide the reference sample for comparing (u-b), (b-g), and (u-g), using the 1σ member color scatter and the purity of the identification algorithm. Across the cluster sample and redshift range probed, (b-g) consistently has the smallest scatter and highest purity. The authors therefore recommend (b-g) for red-sequence-based membership selection in future SuperBIT analyses. The finding is scoped to the tested sample and redshift range; the abstract reports no numerical performance values.
PublicMaps of how galaxies are distributed within a cluster can help trace its stellar mass, but images taken in several color bands do not always make it easy to tell which galaxies belong to the cluster. Researchers tested three color comparisons using images from SuperBIT’s April 2023 balloon flight, checking their performance against galaxies already identified as cluster members through spectroscopy. The (b-g) comparison showed the least variation among confirmed members and the highest purity, meaning the largest fraction of selected galaxies were genuine members. The researchers recommend this color for future cluster-membership studies with SuperBIT, within the range of cluster distances tested.
Young explorerGalaxies can gather in big groups, but it can be hard to tell which ones belong together. Scientists used pictures from a telescope carried by a balloon and tried three ways of comparing galaxy colors. They checked their choices using galaxies already known to belong to the groups. One color comparison, called (b-g), worked best in the groups they tested: the known members had more similar colors, and it picked out members more reliably. The scientists suggest using that comparison in future studies.
Xiaowen Zhang, Patrick Lachance, Rupert A.C. Croft+2 more
AstronomerThe authors present a cosmology-conditioned GAN for particle-phase-space super-resolution of N-body simulations, jointly generating displacements and velocities from evolved low-resolution fields and five ΛCDM parameters: Ωm, Ωb, h, ns, and σ8. A single model is trained on 100 matched Quijote Latin-hypercube pairs at z = 0, mapping 512³ to 1024³ particles in 1 h⁻¹ Gpc boxes. Tests on ten cosmologies excluded from training reproduce the broad matter distribution and cosmology-dependent changes in clustering and halo abundances. Across 0.1 < k < 3 h Mpc⁻¹, the mean of the per-cosmology maximum absolute power-spectrum errors is 3.6%. Friends-of-friends halo abundances agree with high-resolution simulations within 15% in the analyzed mass bins below 10^14.8 h⁻¹ solar masses, but satellite abundances and occupations show larger, mass-dependent discrepancies. Corrections derived at one near-fiducial cosmology reduce a shared component of systematic error in the other nine test cosmologies. Calibration also reduces mean shifts in all five parameters in a power-spectrum-based inference test. These are simulation-validation results; applications to nonlinear structure and field-level cosmological inference are intended subsequent uses.
PublicResearchers developed an AI model that adds detail to computer simulations of how matter is distributed and moves in the universe. It is given both a lower-resolution simulation and five parameters describing the simulated cosmology. After training on 100 paired simulations, it was tested on ten cosmologies not used in training. It recovered the broad matter distribution and how clustering and the numbers of matter clumps change between cosmologies. For one clustering measure, the average of the largest errors in each test cosmology was 3.6% over the tested range. Counts of larger matter clumps agreed within 15% in the analyzed mass ranges, but smaller satellite clumps remained less accurate. Corrections based on one test cosmology improved some shared errors in the others and reduced parameter shifts in an inference test. The work concerns simulated universes, not direct observations, and its proposed scientific applications still require further study.
Young explorerScientists make pretend universes on computers using lots of tiny dots. They taught an AI to turn a less-detailed pretend universe into one with more dots, showing where the dots are and how they move. It worked fairly well on new kinds of pretend universes, but some smaller groups of dots were still not quite right. A correction helped with some mistakes. This was a computer test, not a picture of the real universe.
Dario Primignani, Lorenzo Pizzuti, Antonaldo Diaferio+1 more
AstronomerThe study tests Refracted Gravity (RG), a phenomenological modification of the Poisson equation with an effective gravitational permittivity dependent on baryonic density, designed to mimic dark-matter effects. Member-galaxy kinematics from 74 CIRS galaxy clusters are analysed in three stacks of increasing velocity dispersion to mitigate systematics arising from departures from dynamical equilibrium and spherical symmetry. Using MG-MAMPOSSt, the authors reconstruct the RG gravitational potential and jointly infer RG parameters and gas and stellar mass-profile parameters under broad, physically informed baryonic priors. Across the three main stacks, inferred vacuum permittivity values, epsilon_0, range from 0.04 to 0.37, depending on the hot-gas model. The constraints are mutually compatible within quoted uncertainties and overlap previous cluster-scale estimates. Selecting less-disturbed clusters reduces the sensitivity of this agreement to gas parametrisation. The results characterize the dependence of cluster-scale RG constraints on baryonic modelling and sample selection; they do not establish RG as the correct description of gravity.
PublicResearchers used the motions of galaxies in 74 galaxy clusters to test Refracted Gravity, a proposed change to gravity intended to reproduce effects attributed to dark matter. In this model, gravity depends on the density of ordinary matter. They combined clusters into three groups based on the spread of galaxy speeds to reduce some sources of error. Their estimates of a key model parameter ranged from 0.04 to 0.37, depending on how they described the clusters’ hot gas. The estimates agree within their uncertainties and overlap earlier cluster studies. Choosing less-disturbed clusters made that agreement less dependent on the gas description. This is a test of how the model’s estimates depend on modelling choices, not proof that it replaces dark matter.
Young explorerScientists watched how galaxies move in 74 big groups. They tested an idea that changes how gravity works depending on how much ordinary stuff is nearby. Their answers depended on how they described the hot gas in those groups. The answers could agree, but this does not prove the idea is right.
Igor Bandos, Bohdan Zvorskyi
AstronomerThis theoretical analysis finds that Maxwell electrodynamics interacting with a planar Chern-Simons interface admits no plane-wave solutions localized on the interface. The authors re-examine Kaloper’s derivation in Phys. Rev. D 114 (2026) L051903 and identify omitted terms in an intermediate equation; restoring them changes the earlier conclusion. They also argue that the method used in arXiv:2606.12513 to reproduce that conclusion is inconsistent. These are mathematical findings about the specified model, not observational results.
PublicThe paper revisits a theoretical claim that electromagnetic waves could remain confined to a flat boundary with a particular interaction called a Chern-Simons interaction. The authors report that an earlier calculation left out terms and that including them shows the model does not support the claimed boundary-confined plane waves. They also find a separate method used to support the earlier claim inconsistent. The work checks mathematical descriptions rather than reporting an experiment or astronomical observation.
Young explorerScientists checked some math about whether a certain kind of light wave could stay close to a flat surface in a special model. They found that an earlier calculation had left out some pieces. When those pieces are included, the math says those waves cannot stay there as claimed. This was a check of a model, not something they watched happen.
Mian Zhu, Jun Tao, Peng Wang
AstronomerThe authors introduce quasinormal-mode collider spectroscopy (QCS), a theoretical framework for organizing and predicting nonlinear black-hole ringdown responses through mode interactions and intermediate states. They establish that, at an isolated, nondegenerate intermediate pole, the cubic strain residue factorizes into an excitation amplitude and a quadratic conversion coefficient. This yields rank constraints across output channels and choices of second-order initial data, offering consistency tests of the intermediate-mode description. They also establish that the intermediate pole residue can be reconstructed from its horizon and infinity radiation. With the first-order field and third-order data fixed, this reconstruction extends to the full cubic waveform difference produced by changing second-order initial data. These are structural theoretical results, not reported observational detections, and connect lower-order radiation to higher-order observables.
PublicAfter a black-hole merger, the remnant has characteristic oscillations that encode its properties and can test gravity under extreme conditions. These oscillations have usually been treated as independent, but nonlinear effects can reveal how they interact. The authors introduce a theoretical framework called quasinormal-mode collider spectroscopy to describe those interactions. Under a specific condition—an isolated intermediate response without degeneracy—they show that part of the third-order signal separates into two factors, creating consistency checks for the interaction model. They also show how that intermediate contribution can be reconstructed from radiation at the black-hole horizon and at infinity. With certain other inputs held fixed, the reconstruction also captures changes in the full third-order waveform caused by changing second-order initial data. The abstract reports theoretical results, not a detection of these effects.
Young explorerAfter two black holes join, the new black hole can wobble in different ways, a bit like a bell ringing with several notes. Scientists made a new mathematical way to study how those wobbles affect one another. Their calculations show that, in certain cases, simpler parts of the ringing can help them work out more complicated parts. This is a result from mathematics, not a report that they heard these special effects in a real black hole.
L. Giani, C. Howlett, K. Said+2 more
AstronomerThe authors propose an effective model for the bias Laniakea may induce in cosmological observables, using its definition from Cosmicflows-4 peculiar-velocity data. They approximate the supercluster as a triaxial ellipsoid with constant expansion rates along its principal axes. After subtraction of the background expansion, the best fits suggest contraction along the two shorter axes and expansion along the longest, with a predicted mean residual expansion of about −1.7 km/s/Mpc. The resulting direction-dependent luminosity-distance corrections are applied to low-redshift Pantheon+ Type Ia supernovae and 63 surface-brightness-fluctuation measurements of massive early-type galaxies from the MASSIVE survey. Within this model, distance corrections are approximately 2–3%, shifting the best-fit Hubble constant by about 0.6 km/s/Mpc for the supernova sample and 1.4 km/s/Mpc for the surface-brightness-fluctuation sample. These model-dependent shifts appear to worsen the Hubble tension.
PublicLaniakea, the supercluster that contains the Milky Way, may affect estimates of how fast the universe expands. The authors propose a model that represents this region as an ellipsoid whose three main directions expand at different rates. Their fits suggest that, relative to the universe’s overall expansion, the region contracts in two directions and expands in the third. This would change calculated galaxy distances by different amounts depending on the direction we look. Applying the model to two nearby-universe datasets—Type Ia supernovae and galaxy surface-brightness fluctuations—the authors obtain distance corrections of about 2–3%. These corrections shift the inferred expansion rate by about 0.6 and 1.4 km/s/Mpc, respectively. The shifts seem to make the disagreement between estimates of the universe’s expansion rate, known as the Hubble tension, worse rather than resolve it; the conclusion depends on the proposed model.
Young explorerOur Milky Way lives in a huge group of galaxies called Laniakea. Scientists made a model—a simplified picture—to see whether the way this group moves could change how far away other galaxies seem. Their model suggests that the group squeezes in two directions and stretches in another, compared with the universe’s usual stretching. Using this model changed their distance calculations a little. It also changed their estimates of how fast the universe grows, and seemed to make those estimates agree less well with other estimates. This is what their model suggests, not something they know for certain.
Armin Hatefi, Ehsan Hatefi, I. Y. Park
AstronomerThe authors investigate a phenomenological model of finite-temperature quantum-gravity corrections to the Hubble parameter by modifying the Cosmic Linear Anisotropy Solving System. Two new density parameters, Omega_Lambda_2 and Omega_Lambda_3, encode off-shell vacuum-bubble contributions from Standard Model fields, including heavy fields that cannot be treated as on-shell radiation; alternatively, they represent corrections to the early plasma’s effective equation of state. Using neural networks and stochastic optimization to analyze their effects on the CMB power spectrum, the authors find a negative Omega_Lambda_2, which they describe as consistent with dimensional regularization, and an improved fit to 2018 Planck data when both parameters are included. These are model-fitting results, not a direct detection of quantum-gravity effects. A first-principles derivation rigorously separating on-shell kinetic-theory content from off-shell vacuum contributions remains absent, and the Hubble tension persists. Higher-order thermal effects and polarization constraints are identified as directions for further investigation.
PublicThis study tests whether proposed temperature-dependent quantum effects could improve our description of how the universe expands. The researchers added two terms to a cosmology computer model and used machine-learning methods to study their influence on the cosmic microwave background, the ancient light left over from the early universe. Including both terms improved the model’s fit to 2018 Planck observations, and one fitted parameter was negative. However, a better fit does not establish that these quantum-gravity effects occur in nature. The model is exploratory, and its underlying contributions have not yet been rigorously derived from fundamental physics. It also does not resolve the Hubble tension, the disagreement over the universe’s expansion rate. The authors suggest further work on temperature effects and constraints from the polarization of the ancient light.
Young explorerScientists made a computer model to explore how the universe grows. They added two new pieces to represent possible tiny effects in the hot, young universe. With those pieces, the model matched measurements of very old light better. But that does not prove the new pieces describe what really happened, and the scientists still need to check the ideas behind them. The model also did not solve a puzzle about how fast the universe is growing.
Caio B. de S. Nascimento, Marilena Loverde
AstronomerThis theoretical study improves models of neutrino and hot dark matter (HDM) wakes—the preferential downstream accumulation of hot particles behind moving cold dark matter structures—and forecasts their detectability under more realistic survey conditions. The forecasts indicate that 2D weak lensing surveys are unlikely ever to detect these wakes. Idealized 3D maps of an HDM tracer could instead yield high-significance detections if the effective free-streaming length is sufficiently small; for an HDM species comprising 1% of total dark matter, present-day k_fs,0 ≳ 0.03 Mpc⁻¹ is an example threshold for SNR ≳ 1, not itself a high-significance detection. The authors identify wakes as a distinctive signature of free-streaming that cannot be mimicked by changes to the background expansion history, including dynamical dark energy. This offers a potential complement to traditional searches for massive neutrinos and other hot dark matter components, rather than a reported observational detection.
PublicMoving structures of cold dark matter can leave a wake where neutrinos or other hot dark matter particles preferentially gather behind them. This study develops better theoretical models and predicts how difficult these wakes would be to detect; it does not report seeing one. The forecasts suggest that two-dimensional weak lensing surveys are unlikely ever to reveal the effect. Idealized three-dimensional maps tracing hot dark matter could detect it strongly under suitable conditions, particularly if the particles' effective free-streaming distance is small enough. Such a wake would provide a distinctive clue to free-streaming that changes in the universe's overall expansion could not imitate, potentially offering another way to search for massive neutrinos and hot dark matter.
Young explorerScientists think tiny particles could gather behind moving clumps of dark matter, making a trail called a wake. They used mathematical models to work out whether we could find these trails, but they have not spotted one in this study. Their predictions say flat maps of space probably would not show them. An ideal map with depth might, if the particles do not travel too far freely. Finding a trail could help scientists learn about these hard-to-see particles.
Yourong Frank Wang
AstronomerThis simulation study compares Lyman-alpha forest flux statistics in ΛCDM and mixed fuzzy-plus-cold dark matter using the Fluctuating Gunn–Peterson Approximation (FGPA). For an axion mass of 10^-24 eV and an FDM fraction of 0.1, the authors evolve dark matter from z = 120 to z = 2, comparing a full Schrödinger–Poisson treatment with a particle-only mixed-dark-matter proxy and a ΛCDM baseline, all sharing random phases. The two mixed models have matched initial total-matter density power but different initial velocity prescriptions, so their differences reflect both an inherited velocity offset and subsequent evolution. At z = 4 and k ≈ 10 h Mpc^-1, their nonlinear matter power spectra differ by about 25%, while the full treatment retains about 44% of the proxy's unfiltered line-of-sight velocity power. At k = 0.1 s km^-1, their flux power spectra differ by 21% at z = 4 and 3% at z = 2, with larger differences toward higher redshift and smaller scales. Within this framework, suppressed initial density power alone does not make the particle-only proxy reproduce the flux statistics; velocities also matter. These are idealised, dark-matter-only results with a prescribed FGPA thermal state and a preliminary neutral-hydrogen-weighted velocity diagnostic. Full hydrodynamical simulations are needed to test robustness to baryonic response and thermal-history uncertainty.
PublicThe researchers used computer simulations to study how a mixture of fuzzy and cold dark matter could affect the Lyman-alpha forest, a pattern of hydrogen absorption in light from distant sources. They compared a simulation that includes fuzzy dark matter's wave behaviour with a simpler particle-based approximation. Although the two mixed-dark-matter models started with matching density-pattern power, they used different starting velocities. Their predicted absorption-pattern power differed by 21% at redshift 4 and 3% at redshift 2 at the scale quoted in the study, with larger differences at earlier times and smaller scales. The comparison indicates that motion matters, not just how dark matter is distributed, and that the simpler approximation does not reproduce these predictions within the tested framework. The differences cannot be attributed solely to wave evolution because the initial velocities also differed. These are simulation results, not measured absorption differences: the study models only dark matter and estimates absorption using an assumed gas temperature state. More complete simulations including gas physics are needed to see whether the differences persist.
Young explorerScientists made computer models of invisible stuff called dark matter. In one model, some of it behaved like waves; in another, it was treated as little particles. They used the models to guess how hydrogen would block some light travelling through space. The guesses were different, showing that how the dark matter moves matters, not just where it is. But the models also started with different motions, so waves alone may not explain the difference. The scientists still need models that include how the gas moves and heats up to check whether this happens outside their simplified computer worlds.
Wassim Kabalan, Arianna Rizzieri, Wuhyun Sohn+6 more
AstronomerThe authors present a JAX-powered extension of fgbuster’s parametric component-separation formalism within FURAX, designed for CMB polarization analysis with spatially varying foreground spectral energy distributions. Pixels are grouped by shared foreground spectral parameters, and thousands of configurations are scanned to assess the trade-off between model complexity and residual systematic contamination. Vectorized GPU processing supports spectral-likelihood evaluation, map reconstruction, and diagnostics across tens of thousands of configurations, noise realizations, and sky regions. The implementation reports up to approximately 100-fold speed-up over fgbuster’s scipy TNC optimizer on GPUs, with more robust results. In LiteBIRD-like simulations, an optimized K-means configuration lowers the 68% upper limit on the tensor-to-scalar ratio r by approximately 30% relative to a fixed, previously derived multi-resolution configuration, while maintaining competitive statistical uncertainties. This improvement is demonstrated in simulations, not observational data.
PublicResearchers developed faster software to separate polarization in the cosmic microwave background from foreground signals whose frequency dependence changes across the sky. The method groups sky pixels with similar foreground properties and tests many grouping choices, balancing a more detailed model against unwanted signal left behind. Using graphics processors, the software runs up to about 100 times faster than the comparison optimizer and is reported to give more robust results. In simulations resembling LiteBIRD data, an optimized grouping method reduced an upper limit on the parameter r, which compares tensor and scalar contributions, by about 30% relative to a previously developed fixed grouping scheme, while keeping statistical uncertainties competitive. These are software and simulation results, not a detection in the real sky.
Young explorerScientists want to study a very old light in the sky, but other light gets mixed in with it. They made a fast computer tool that puts little pieces of the sky into groups and tries lots of ways to separate the light. In pretend sky tests, one way of making the groups worked better than an older way. That is promising, but the tests do not show that the tool has found anything new in the real sky.
Vaishali R, Dipayan Mukherjee, Akshank Tyagi+1 more
AstronomerHigh-precision CMB observations have revealed anomalies that may indicate violations of statistical isotropy, but do not establish such violations. The authors introduce a geometric real-space framework complementary to the Bipolar Spherical Harmonics (BipoSH) formalism. Averaging the angular correlation function over rotated configurations with Wigner-matrix weights systematically isolates statistically anisotropic components and provides a geometric interpretation of the rotational-symmetry breaking encoded by BipoSH coefficients. For an analytical dipole-modulation model, they numerically implement these rotational averages and demonstrate agreement with the corresponding harmonic-space measures. This is a model-based demonstration, not a new observational detection of anisotropy. Potential advantages include extracting anisotropy information at a given multipole directly from the correlation function without computing BipoSH coefficients to arbitrarily high internal ranks. The authors also argue that real-space temperature-map analysis can circumvent partial-sky effects that complicate harmonic-space methods. Applications to primordial non-Gaussianity, CMB polarization, weak gravitational lensing, and general random fields on a sphere are envisaged rather than demonstrated here.
PublicThe cosmic microwave background is ancient light whose patterns can be studied across the sky. Some observed anomalies suggest that its statistical properties might depend on direction, although this is not established. This paper presents a new way to investigate that possibility by working directly with correlations between sky directions. The method averages these correlations over rotated arrangements, using mathematical weights to separate out direction-dependent patterns. In a mathematical model with a particular directional modulation, numerical tests agree with an existing method that represents sky patterns using spherical harmonics. That agreement tests the technique; it does not show that the real sky has this modulation. The authors suggest that the approach could simplify some calculations and avoid complications associated with observing only part of the sky. They also propose broader applications, which are not demonstrated in this work.
Young explorerScientists study very old light in the sky. Some patterns look surprising, but scientists are not sure whether they really change with direction. This paper offers a new way to check, by turning patterns around in a calculation and comparing them. The new way matched an older way in a pretend mathematical sky. That is a useful test, but it does not prove that the real sky is different in different directions.
Jianfeng Meng, Xiaofeng Yang, Yunliang Ren+4 more
AstronomerThe study combines high-redshift GRB distance moduli from the 15-year Fermi/GBM GOLD and FULL samples with Pantheon+ Type Ia supernovae to compare flat ΛCDM, wCDM, IDE-ρ_de, and IDE-ρ_c. The Amati relation is calibrated using the corresponding low-redshift GRBs; its intercept–slope covariance is propagated into a full, non-diagonal distance-modulus covariance, while an effective residual scatter is fitted jointly with cosmological parameters. GOLD and FULL give very similar constraints on the main cosmological parameters. With either full or diagonal GRB covariance, the IDE models' likelihood improvements do not offset their additional parameters under BIC, which favors ΛCDM. Relative to supernovae alone, GRBs generally add modest constraining power. These distance data provide no significant evidence for either IDE interaction tested, rather than ruling out interacting dark energy in general.
PublicResearchers used Type Ia supernovae and gamma-ray bursts to compare explanations for how the universe expands. Gamma-ray bursts extend these distance measurements farther into the universe, but require careful calibration and accounting for uncertainty. The team tested the standard ΛCDM model alongside three alternatives, including two interacting dark energy models. Two collections of gamma-ray bursts gave very similar results, and the bursts generally added only modest information beyond the supernovae. A statistical comparison that penalizes extra model complexity favored ΛCDM: the interacting models did not improve the fit enough to justify their additional adjustable parameters. The measurements therefore show no significant evidence for the two dark energy interactions tested, but do not prove that all such interactions are absent.
Young explorerScientists want to understand how the universe is growing. They used exploding stars and bright flashes called gamma-ray bursts to help measure distances in space. They carefully checked how uncertain those measurements were and compared several ideas about the universe. The bright flashes added a little extra help, but the usual idea worked best in a test that also counts how complicated each idea is. They did not find a clear sign of the two kinds of dark energy interaction they looked for. That does not mean those ideas are impossible.
Sarah C. Johnston, Simon May, Tibor Dome+5 more
AstronomerNumerical simulations with AxiREPO examine the halo mass function (HMF) in mixed cold and fuzzy dark matter cosmologies, with an ultralight axion-like mass of 10^-24.5 eV and fuzzy dark matter fraction f ≤ 0.3. A new grid-based halo finder combines the particle-based cold and wave-like fuzzy components into a unified density field. In the simulations, fuzzy dark matter traces the large-scale cold dark matter distribution but suppresses small-scale structure through wave interference, reducing low-mass halo abundance. Increasing the fuzzy fraction systematically lowers the HMF and changes its high-mass slope, with effects depending on redshift and fraction. A phenomenological suppression model maps cold dark matter HMFs to mixed-dark-matter HMFs, reproducing the simulated functions to approximately 0.1–0.2 dex over the explored range 1 ≤ z ≤ 4 and f ≤ 0.3. This offers an efficient alternative to dedicated simulations within the tested parameter space; the findings are simulation results, not observational measurements.
PublicThe researchers used computer simulations to study how cosmic structure changes if dark matter is a mixture of a cold component and an ultralight, wave-like component called fuzzy dark matter. In the models explored, fuzzy dark matter makes up no more than 30% of the total. The team developed a way to identify dark matter concentrations, called haloes, by combining both components into one density map. The simulations show that fuzzy dark matter follows the cold component on large scales, while interference between its waves reduces small-scale structure and leaves fewer low-mass haloes. Increasing its share also changes the abundance of more massive haloes, and the effects vary with cosmic epoch. The researchers built a mathematical approximation that reproduces the simulated halo abundances to about 0.1–0.2 dex within the tested range, allowing faster predictions without a new simulation for every case. These results describe simulated universes and do not establish that real dark matter has this mixture.
Young explorerScientists used computers to pretend to make a universe with two kinds of dark matter, stuff in space that we cannot see. One kind acts like tiny particles, and the other acts like waves. In their pretend universes, adding more of the wave-like kind meant fewer small clumps of dark matter formed. The scientists also made a math shortcut that gives answers close to their computer tests. This tells us what might happen with this mixture, not that the real universe is definitely made this way.
Ottavia Truttero, Maria Tsedrik, Joe Zuntz+4 more
AstronomerThis mock-based LSST Y1/Y10 3x2pt analysis examines the trade-off between nonlinear modelling complexity and scale cuts, using BACCO to model HEFT galaxy bias and baryonification-based feedback. A linear bias model yields percent-level unbiased constraints on Ωm and σ8 only up to kmax = 0.1 h/Mpc; extending to smaller scales requires a perturbative treatment. A minimal bias variant with fixed higher-order terms remains unbiased for these constraints in ΛCDM even at kmax = 0.7 h/Mpc. Higher-order bias can mimic baryonic suppression, but baryonic feedback cannot reproduce the full range of higher-order bias behaviour within BACCO's allowed baryonification parameter range. The analysis suggests that total neutrino mass could be detected in both Y1 and Y10 using scales with k ≥ 0.5 h/Mpc, at least when photometric-redshift uncertainties and related nuisance parameters are precisely known. However, the inferred mass is not robust across equally plausible mock scenarios and can be significantly biased by the minimal bias model. These are modelling and forecast findings, not observational detections. The work also introduces MGL, an independent open-source analysis pipeline.
PublicThe researchers use mock LSST data to test how reliably future surveys could measure the Universe's matter content, the strength of matter clustering, and the total mass of neutrinos. Smaller-scale patterns offer useful information, but their interpretation is complicated by how galaxies trace matter and how ordinary matter changes those patterns. A simple galaxy model works only over a restricted range of scales. A more elaborate but still simplified model recovers the matter and clustering parameters accurately in the tested ΛCDM setting, yet can give a substantially biased neutrino mass. The study forecasts a possible neutrino-mass detection from both the first-year and ten-year datasets if sufficiently small scales are used and certain uncertainties are precisely known. It does not report an actual detection: equally plausible mock scenarios yield different inferred masses. The authors also introduce an open-source analysis pipeline.
Young explorerScientists practiced with pretend sky data to see what a future sky survey might teach us. They tried different ways to explain how galaxies and matter make patterns. A simple explanation worked for some patterns, but smaller patterns needed more care. They might be able to learn how much tiny particles called neutrinos weigh. But different explanations could give the wrong answer, so this is a possibility to test, not something they have already measured.
Michael M. Wyatt, Nikolaos Triantafyllou, Steven R. Furlanetto+4 more
AstronomerThis study introduces the persistent-homology Betti-0 curve as a summary statistic for Lyman-alpha emitter (LAE) clustering and forecasts its ability to constrain the global neutral hydrogen fraction during reionization. The authors forward-model LAE observations with 21cmFAST, adding Lyman-alpha emission in post-processing and accounting for cosmic variance, within the SILVERRUSH catalog framework at z = 5.7 and 6.6. Fisher-information comparisons indicate that the Betti-0 curve performs as well as or better than the angular correlation function (ACF) and void probability function (VPF). The three statistics are most sensitive to different physical scales and therefore provide complementary information. Combining them improves forecast constraints by approximately a factor of two relative to the ACF alone. Predicted minimum uncertainties on the neutral fraction are approximately 0.03 at x_HI = 0.05 and z = 5.7, and 0.07 at x_HI = 0.20 and z = 6.6. These are model-based forecasts, not measured neutral fractions. The results motivate further exploration of persistent homology in wide-field surveys, including those enabled by the Nancy Grace Roman Telescope.
PublicThe way galaxies that emit Lyman-alpha light cluster together could help reveal how much hydrogen remained neutral during the universe's reionization era. This study tests a mathematical tool called the Betti-0 curve, which describes how separate groups in a galaxy distribution connect as the linking scale changes. Using simulated observations designed around the SILVERRUSH catalog and allowing for variation between cosmic regions, the researchers forecast that this tool could match or outperform two existing clustering measures. Because the three measures emphasize different scales, combining them could make neutral-hydrogen constraints about twice as precise as using the angular correlation function alone. These are predictions from modeling, not new measurements of the universe's neutral hydrogen fraction. The authors suggest exploring the approach in future wide-field surveys.
Young explorerLong ago, the universe's hydrogen gas was changing. Scientists want to learn about that change by looking at how galaxies bunch together. They tested a new way to count galaxy groups in pretend skies made by a computer. Combining it with two other methods could give better clues. They still need to explore how well it works with real skies.
Luis A. Anchordoqui, Alek Bedroya, Dieter Lüst
AstronomerThis theoretical study revisits primordial black hole production through inflation, phase transitions, and cosmic strings within the Swampland-motivated Dark Dimension Scenario. Applying quantum gravity constraints, the authors argue that viable production mechanisms necessarily yield five-dimensional primordial black holes, unless exotic low-energy physics intervenes. They also find that cosmic-string-produced primordial black holes can have lifetimes comparable to the age of the universe. As a possible observational implication, they discuss a connection to KM3NeT's recent high-energy neutrino detection, whose energy is close to the scenario's five-dimensional Planck scale. This connection is suggested, not established by the detection.
PublicThe paper explores how black holes could have formed in the early universe in a theoretical framework called the Dark Dimension Scenario. The authors examine three possible routes: inflation, phase transitions, and cosmic strings. Under this framework's quantum gravity constraints, they conclude that viable routes would produce five-dimensional black holes, unless unusual new physics operates at low energies. Their calculations also indicate that black holes formed from cosmic strings could live for about as long as the universe has existed. They suggest a possible link to a high-energy neutrino recently detected by KM3NeT because its energy is close to a characteristic quantum gravity energy scale in the model. That link remains a possibility, not evidence that these black holes have been found.
Young explorerScientists used a theory with an extra dimension to think about how black holes might have formed when the universe was very young. In their theory, the black holes would be five-dimensional, unless nature has some unusual new rules. Some made from things called cosmic strings could last about as long as the universe has been around. The scientists also wonder whether a very energetic tiny particle that was detected could be connected to these black holes, but they do not know that it is.
Andrea Begnoni, Walter Del Pozzo, Matteo Pegorin+2 more
AstronomerThis study forecasts tests of General Relativity with binary black hole mergers observed by the proposed third-generation Einstein Telescope (ET). It uses Fisher-matrix parameter-estimation simulations for large source catalogs and combines events in a Bayesian hierarchical framework, comparing ET configurations and constraining parametrized deviations in inspiral post-Newtonian coefficients. The forecasts suggest that about four months of ET observations could tighten current LIGO-Virgo-KAGRA GWTC-3 bounds by roughly four orders of magnitude for the dipole radiation term and about two orders for higher-order coefficients. The study also assesses the detection counts needed to confidently identify deviations at different post-Newtonian orders and for different configurations. These are simulation-based forecasts, not observed improvements or evidence of departures from General Relativity.
PublicGravitational waves from merging black holes let scientists test Einstein's theory of gravity, General Relativity. Existing LIGO-Virgo-KAGRA observations have already provided stringent checks of its predictions. This study uses simulations to estimate how much more precisely the proposed Einstein Telescope could test the theory by combining many mergers. The forecasts suggest that roughly four months of observations could make limits on a possible dipole-radiation contribution about 10,000 times tighter than current GWTC-3 limits, and limits on higher-order contributions about 100 times tighter. The researchers also compare telescope designs and assess how many detections would be needed to confidently identify departures from the theory. These improvements are predictions, not measurements, and the study does not report a failure of Einstein's theory.
Young explorerWhen two black holes come together, they make ripples in space. Scientists use those ripples to check Einstein's ideas about gravity. In this study, they used computer simulations to imagine what a planned detector called the Einstein Telescope might learn from lots of black hole pairs. Their calculations suggest it could check some parts of Einstein's ideas much more carefully than today's detectors. But these are guesses based on simulations, not things the new detector has seen, and they do not show that Einstein's ideas are wrong.
K.S. Babu, Sai Charan Chandrasekar, Zurab Tavartkiladze
AstronomerThis theoretical study presents three generalizations of the DFSZ axion model in which a gauged U(1)_F flavor symmetry generates hierarchical fermion masses and mixings through the Froggatt–Nielsen mechanism. An accidental global Peccei–Quinn symmetry with a nonzero QCD anomaly supplies an axion that addresses the strong CP problem, while the gauge symmetry protects its potential against quantum-gravity corrections. Explicit ultraviolet completions of the flavor sectors preserve this axion quality, and the right-handed neutrino mass scale is identified with the Froggatt–Nielsen scale. Within these models, the axion also acts as a flavon, yielding testable predictions for flavor-changing neutral-meson decays. The authors report that the models can provide the required axion dark-matter relic abundance without cosmological domain-wall problems and generate baryon asymmetry through calculable leptogenesis at the right order of magnitude. These are model results and predictions, not reported observational detections.
PublicThe authors propose three theoretical models that connect several puzzles in particle physics and cosmology. A shared mathematical framework explains why matter particles have very different masses and mixings, while producing a hypothetical particle called the axion that addresses the strong CP problem in the theory of the strong nuclear force. The framework also protects the axion mechanism from disruptive quantum-gravity effects, including in the authors’ more fundamental versions of the models. In these models, axions can supply the required amount of dark matter without creating problematic boundaries between cosmic domains. The models also generate a matter–antimatter imbalance of roughly the required size through a process called leptogenesis. They predict flavor-changing decays of neutral mesons that could be tested. The abstract reports theoretical calculations, not evidence that these axions have been observed.
Young explorerScientists made three math models to connect some big puzzles: why tiny particles have different masses, what the universe’s invisible dark matter could be, and why there is more matter than antimatter. Their models use a possible tiny particle called an axion. In the models, axions can make the needed dark matter, and another process can make about the needed matter–antimatter difference. The models also suggest changes in some particles that scientists could look for. These are ideas worked out with math, not a discovery of the axion.
Siddhartha Bandyopadhyay, Ujjal Kumar Dey
AstronomerThis theoretical study calculates Stodolsky-effect energy shifts using the most general neutrino–electron interactions below the electroweak scale, considering all Lorentz-invariant operators respecting SU(3)⊗U(1) symmetry. Both Dirac and Majorana neutrinos are treated. Beyond the Standard Model contribution, the authors find nonzero contributions only from non-standard neutrino interactions and tensor interaction terms. They examine implications for possible cosmic neutrino background detection and discuss how a considerable asymmetry in that background could affect the scenario. The abstract reports calculations, not a detection, and gives no numerical energy shifts or detection sensitivities.
PublicThe researchers calculate how neutrinos interacting with electrons could produce changes in electron energy known as the Stodolsky effect. They consider two possible types of neutrinos and a broad range of interaction rules. Their calculations identify which interactions could contribute beyond those in the Standard Model of particle physics. They explore whether these energy changes might help detect the cosmic neutrino background and discuss the possible role of an imbalance in that background. This is a theoretical investigation, not a reported detection.
Young explorerNeutrinos are tiny particles. Scientists used math to study how they might change the energy of other tiny particles called electrons. They tried different rules for how the particles could interact. These changes might someday help scientists find the neutrinos that make up the cosmic neutrino background, but this study did not find them.
D. Kraiko, A. Racioppi
AstronomerThis theoretical study revisits natural inflation in metric-affine gravity with a periodic non-minimal coupling between the inflaton and the Nieh-Yan term. With that coupling alone, the strong-coupling limit gives linear-inflation predictions and does not restore the viability of natural inflation. Adding an analogous non-minimal coupling to the Ricci scalar allows agreement with data, including for a sub-Planckian periodicity scale and non-minimal couplings of order unity. These are conclusions about the model’s predictions and compatibility with data, not an observational detection of the proposed couplings.
PublicThe researchers examine a version of natural inflation, a theory of rapid expansion in the early universe, using a modified framework for gravity. One proposed periodic interaction between the field driving inflation and a gravitational term called the Nieh-Yan term does not, by itself, make the theory agree with data; at strong interaction strength, its predictions approach those of linear inflation. Adding a second interaction involving the Ricci scalar, which describes spacetime curvature, allows agreement with data. The model can remain viable with a periodicity scale below the Planck scale and relatively modest interaction strengths. This is a theoretical compatibility result, not evidence that these interactions actually occurred.
Young explorerScientists are checking an idea about how the universe might have grown very quickly when it was very young. In their maths, adding one new connection to gravity is not enough to make the idea fit what we know about the universe. Adding a second connection can make it fit. That makes the idea worth considering, but it does not prove that the universe really grew that way.
Simon Cléry, Alejandro Ibarra, Onur Yonar
AstronomerThe authors propose a leptogenesis mechanism in which right-handed neutrinos exceed the Universe’s maximum temperature and are never produced on-shell, either thermally or non-thermally. A new scalar field, φ, lighter than these neutrinos and coupled to them through a Yukawa interaction, undergoes four-body decay into two lepton doublets and two Higgs doublets through off-shell right-handed neutrinos. The authors derive the decay’s CP asymmetry from tree–loop interference and show theoretically that the resulting baryon asymmetry can reproduce the observed value in two scenarios: φ drives reheating, or φ is a generic scalar maintained in thermal equilibrium with the plasma. This is a proposed mechanism, not an observational detection of the new particles.
PublicThe paper proposes a way to explain why the Universe has more matter than antimatter. In this theoretical scenario, very heavy right-handed neutrinos are never produced as real particles, but they can still act as virtual intermediaries in the decay of a new, lighter particle. The authors calculate an imbalance between matter-related and antimatter-related decay processes and show that the mechanism can account for the observed matter excess. It can work whether the new particle reheats the Universe or stays in thermal balance with the surrounding hot particles. The study presents a possible explanation, not evidence that these proposed particles exist.
Young explorerThe Universe has more matter—the stuff that makes stars and people—than antimatter, its opposite partner. The scientists suggest that a new kind of tiny particle could break apart in a way that helps make this extra matter. Their calculations say the idea could work whether that particle helps heat the young Universe or stays mixed with its hot particle soup. This is an idea they worked out, not a new particle they have found.
Rodrigo Calderon, Eric V. Linder
AstronomerThe authors study effective dark-energy equation-of-state crossings of w = -1 in Horndeski gravity with shift-symmetric terms and a linear potential. They emphasize the role of a nearly conserved scalar charge, report strong predictivity for early phantom behavior, and identify three crossing mechanisms. None reproduces the conditions suggested by current data particularly well. Their main conclusion is that the less elaborate models considered, whose potentials lack a cosmological constant and which cross w = -1 only once, struggle to fit current data. These are theoretical model findings, not an observational detection of a crossing. An online interactive application lets readers solve the evolution equations and explore alternative scenarios.
PublicThe researchers explore modified-gravity models in which the behavior of effective dark energy passes through a reference value called w = -1. A quantity associated with the models’ scalar field stays nearly constant and helps tightly constrain their early behavior. The team identifies three ways this transition can happen mathematically, but none matches the conditions suggested by current observations very well. The difficulty is especially important for simpler models that leave out a cosmological constant and make the transition only once; it is not a rejection of all modified-gravity models. The authors also provide an online tool for exploring how different model scenarios evolve.
Young explorerScientists made math models to explore how dark energy might behave in the universe. They found three ways it could change from one kind of behavior to another. But none of those ways fits the clues we have about the universe very well. Their simpler models have particular trouble. This is a finding about their math models, not a change they watched happen in the sky. They also made an online tool so people can try different versions of the models.
Arturo de Giorgi, James Ingoldby, Valentin V. Khoze+1 more
AstronomerThis theoretical study revisits metastable cosmic strings as a possible explanation of the nanohertz stochastic gravitational-wave background reported by Pulsar Timing Array experiments. A minimal dark-sector model uses a complex Higgs doublet to break SU(2) × U(1) to U(1)_IR at one scale, predicting metastable Z-strings with monopole-like endpoints. The authors find that, when the string-forming transition occurs in a thermal plasma, thermally induced nucleation on the string worldsheet dominates over zero-temperature monopole nucleation. They obtain T_nuc from a one-loop finite-temperature effective potential with daisy resummation, adopt it as the reference string-formation scale, and evaluate the worldsheet bounce action across parameter space. Requiring a PTA-compatible signal selects a narrow region in the plane of the dark weak mixing parameter sin²θ_w and √β, where β is the squared Higgs-to-Z mass ratio. Thermal effects shift this region toward lower dark fine-structure constant α′ and larger monopole-to-string-tension ratio κ. Compatibility with the reported background does not establish cosmic strings as its source.
PublicThe study explores whether temporary cosmic strings—hypothetical threadlike defects in the universe—could explain the low-frequency gravitational-wave background reported by Pulsar Timing Array experiments. In the proposed dark-sector model, strings can break through the creation of defects at their ends. The calculations indicate that heat in the surrounding plasma makes a heat-driven breakup process more important than the process calculated at zero temperature. Including these thermal effects substantially changes which model settings could produce a signal compatible with the reported background, leaving only a narrow allowed region. This is a theoretical explanation under investigation, not a detection of cosmic strings.
Young explorerScientists have reported very slow ripples in space. This study asks whether tiny, invisible threads could help explain them. In the scientists’ calculations, heat helps these pretend-for-now threads break apart and changes which kinds might explain the ripples. Nobody has shown that these threads are really there.
Marcos H. Cruz, Miguel Cruz, Joel Saavedra+1 more
AstronomerThis theoretical study uses the generalized second law (GSL) to constrain generalized horizon entropy proposals at the homogeneous-background level. In a modified Friedmann framework specified by an arbitrary f(H), allowing the apparent horizon and cosmic fluid to be out of thermal equilibrium yields model-independent bounds on the asymptotic scaling S_A proportional to A^k. Phantom evolution requires k >= (3ω−1)/(2ω), where ω is the total fluid equation-of-state parameter, while quintessence requires the complementary upper bound. Exact thermal equilibrium enforces k <= 2 through the dynamical coupling. As the phantom divide is approached, the bounds converge to k = 2, thermodynamically associating smooth crossing with quadratic entropy-area scaling and a limiting logarithmic gravity framework. Applications constrain many representative entropy proposals, while multiparameter constructions are naturally compatible with the required asymptotic behavior. The authors also extend the criterion to derivative-dependent f(H, dH/dt) cosmologies. These are theoretical constraints, not observational findings.
PublicMany proposed descriptions of cosmic expansion assign different entropy laws to the universe’s apparent horizon. This theoretical study argues that the generalized second law of thermodynamics can help distinguish among them. For models treating the universe as spatially uniform, the authors derive limits on how horizon entropy can scale with horizon area, even when the horizon and cosmic contents are not in thermal equilibrium. Two types of evolution, called phantom and quintessence, impose opposite bounds. As their dividing point is approached, both bounds select entropy proportional to the square of the area, suggesting that this scaling is required for a smooth transition within the framework studied. Many representative proposals are constrained, while models with several adjustable parameters can accommodate the required behavior. The criterion also extends to a broader class of expansion models. No observational test is reported.
Young explorerScientists have different mathematical ideas about how the universe grows. This study uses a rule about entropy to check which ideas can work. In their calculations, two kinds of growth put different limits on those ideas. Where the two kinds meet, the limits point to one special rule for the universe’s boundary. This is a result from mathematics, not something the scientists saw through a telescope.
Alexander Stewart
AstronomerThis theoretical study analyzes cosmological stasis in coupled dark matter–dark energy models where a scalar field drives dark energy and determines the dark matter mass, motivated by the Dark Dimension scenario. An autonomous-system treatment including baryons and radiation shows that exact stasis requires exponential slopes along the trajectory; running slopes yield exact stasis or drifting quasi-stasis depending on integrability. Constant-abundance solutions correspond to stationary solutions of coupled quintessence, interpreted here as stasis epochs with calculable lifetimes and exits. When anchored to measured abundances at matter–radiation equality and today, the model's stasis region cannot accelerate, regardless of initial conditions. The total equation of state is never phantom, although effective dark energy inferred through a ΛCDM fit can appear phantom. In the Dark Dimension realization, imposing dark fifth-force bounds excludes future capture into stasis for geometric sources of the potential. Dark matter production from the Standard Model brane permits an additional stasis solution that the standard scenario does not reach. These theoretical solutions give parameter-space exclusions independent of initial conditions; they are not observations of a stasis epoch.
PublicThe researchers explore a theoretical possibility called cosmological stasis: an era when the relative shares of the universe's ingredients stay constant, rather than the universe itself standing still. In their model, a field responsible for dark energy also controls the mass of dark matter. They derive conditions for a steady balance or a slowly drifting near-balance, and work out how such periods can end. Using measured cosmic abundances at two stages of cosmic history to constrain the model, they find that its stasis phase cannot produce accelerating expansion, whatever its starting conditions. They also find that the combined cosmic contents never have a 'phantom' equation of state, although fitting this model's behavior with the standard ΛCDM framework could make dark energy appear to have one. For the motivating Dark Dimension scenario, limits on an extra force acting on dark matter rule out future entry into stasis for the potential sources considered. Another stasis solution is possible with dark matter production from a Standard Model brane, but the standard scenario does not reach it. These are mathematical results about a proposed model, not evidence that the universe has experienced stasis.
Young explorerImagine the universe has a recipe with different ingredients, including dark matter and dark energy. Scientists used math to ask whether the shares of those ingredients could stay the same for a while, even as the universe grows. In their pretend-universe model, one field links dark energy to how much mass dark matter has. They found rules for when the recipe could stay steady and when it could change. After checking the model against measured amounts in our universe, they found that its steady-recipe stage cannot make the universe grow faster and faster. This is an idea studied with math, not something they have seen happen in the sky.
