Neal Weiner, Soubhik Kumar, Wenzer Qin+3 more
AstronomerThe study tests a redshift-localized early reionization contribution motivated by enhanced small-scale primordial overdensities, which could collapse into halos around z ∼ 100 and host stars and black holes. A temporary ionizing episode followed by recombination could leave low ionization approaching cosmic dawn while increasing optical depth with comparatively weak low-ℓ polarization signatures. Fits to a broad suite of cosmological data show an approximately 2–2.5σ preference for this additional component, not a confirmed detection. Across the tested Planck PR3 and PR4 processing choices, the inferred contribution is consistently Δτ_burst ∼ 0.012, with 0.001 < Δτ_burst < 0.022 at 95%, and total τ ∼ 0.073. The preferred epoch is processing-dependent: HiLLiPoP favors z ∼ 45, CamSpec z ∼ 100, and plik z ∼ 165. Conditional on a source at 40 ≲ z ≲ 150, the authors predict that LiteBIRD should detect it and Simons Observatory should constrain it.
PublicCould the universe have experienced an extra, temporary episode when its gas became ionized very early in its history? The researchers test a scenario in which unusually dense small regions formed early, allowing stars and black holes to free electrons from atoms. The electrons could later have recombined, leaving the gas mostly neutral again before cosmic dawn. Their analysis of cosmological data finds a modest statistical preference for this extra episode, but does not establish that it happened. Different versions of Planck data processing favor a similar added contribution to the universe’s optical depth, a measure of how light is affected along its journey, but disagree about when the episode occurred. If it happened within the specified early-time range, the authors predict that LiteBIRD should detect it and Simons Observatory should help constrain it.
Young explorerThe scientists wonder whether stars and black holes formed very early and briefly knocked tiny particles called electrons out of atoms in space. Those electrons might later have joined atoms again. The scientists looked for clues and found a small hint, but they are not sure this happened or exactly when. Future observations might help check the idea.
Pavel Zhelnin, Gonzalo Herrera, Nicholas Kamp+1 more
AstronomerA newly measured correlation between Seyfert neutrino and X-ray luminosities has enabled the first neutrino-based Hubble-constant measurement, currently H0 = 66 (+44/−37) km s⁻¹ Mpc⁻¹. The authors forecast that full-sky IceCube exposures combined with KM3NeT-ARCA and Baikal-GVD by 2030 could narrow this to 66 (+15/−13) km s⁻¹ Mpc⁻¹. They also project a disk-corona luminosity-relation slope of β = 0.72 ± 0.04 for Lν ∝ LX^β, allowing exclusion of the calorimetric value β = 1 at ≥5σ. These improvements are forecasts, not current measurements. An independent determination of Ωm and the dark-energy equation-of-state parameter w would additionally require identifying a high-redshift neutrino-source population, potentially JWST's little red dots, that obeys the same luminosity relation.
PublicA measured link between the neutrino and X-ray brightness of Seyfert galaxies has provided the first neutrino-based estimate of how fast the universe is expanding, though its uncertainty is currently large. The researchers predict that a global network combining IceCube, KM3NeT-ARCA and Baikal-GVD observations by 2030 could substantially improve that precision. They also forecast a more precise test of how neutrino brightness changes with X-ray brightness, potentially ruling out a particular model value. These are projected improvements, not results already achieved. If a population of distant neutrino sources is identified and follows the same brightness relationship, it could also provide independent measurements of the universe's matter content and a property of dark energy. JWST's little red dots are suggested as a possible population, not established here as neutrino sources.
Young explorerSome galaxies send out tiny particles called neutrinos and light called X-rays. Scientists found a link between how brightly the galaxies shine in these two ways and used it to estimate how fast the universe is growing. Their answer is still quite uncertain. They think that using more neutrino telescopes together by 2030 could make the answer clearer. If they find faraway galaxies that send neutrinos and follow the same link, those galaxies might also help them learn about the matter and dark energy in the universe. That part has not happened yet.
S. Schuldt, C. Grillo, S. H. Suyu+7 more
AstronomerThe authors infer H0 and Ωm from the strongly lensed SN Refsdal in MACS J1149.5+2223, augmenting an image-position-based cluster mass model with an extended surface-brightness reconstruction of the supernova host using 77,000 HST pixels. Within flat ΛCDM, they test parameterizations with H0 and Ωm free or H0 alone free, and explore four mass-model realizations addressing constraint weighting and source reconstruction. Their final estimates are H0 = 65.0 (+2.0/−1.8) km/s/Mpc and Ωm = 0.30 (+0.08/−0.09), consistent with previous lensed-supernova results. Adding surface-brightness information halves the H0 uncertainty, yielding a reported 3.0% precision, which the authors identify as the best from a single strong lens to date. Crucially, the total-mass parameterization remains fixed to the previous point-like model, so a known major systematic is not explored. Lens-mass and measured time-delay uncertainties now contribute comparably to the H0 error; further precision gains depend on better time delays and continued systematic control. The prospect of unprecedented precision with sub-percent cluster-scale time delays is forward-looking, not a demonstrated result.
PublicResearchers used the strongly lensed supernova SN Refsdal to estimate how fast the universe is expanding and the fraction of its contents represented by matter. A galaxy cluster bends the supernova’s light, and interpreting this effect requires a model of the cluster’s mass. By adding detailed information about the brightness across the supernova’s host galaxy, the team cut the uncertainty in its expansion-rate estimate in half. Assuming a flat ΛCDM cosmological model, they infer an expansion rate of 65.0 kilometers per second per megaparsec, with about 3% uncertainty, and a matter fraction of about 30%. The authors report that this is the most precise expansion-rate estimate yet obtained from a single strong lens. However, they kept the mathematical description of the cluster’s total mass fixed, leaving an important source of modeling uncertainty untested. More precise measurements of the light’s arrival-time differences and better control of modeling uncertainties could improve future estimates.
Young explorerA big group of galaxies bends light from an exploding star, a little like a lens. Scientists studied that light and a detailed picture of the star’s home galaxy to work out how fast the universe is growing. The extra picture helped make their answer less uncertain. But the answer still depends on how they describe the galaxies that bend the light, and they did not try changing one important part of that description. Better measurements of when the light arrives could help them get a clearer answer in the future.
Anna C. Tsai, Dylan L. Jow, Ue-Li Pen
AstronomerThis theoretical study examines helicity in a primordial gravitational-wave background; it reports no detection. Such a detection would provide compelling evidence for early-universe parity violation and point beyond the standard inflationary picture. Because big bang cosmology lacks time-translation invariance, the authors identify regular and often-neglected irregular solutions as independent degrees of freedom that could carry different, even opposite, helicities, complicating the interpretation of measured net helicity. They introduce a universal helicity efficiency coefficient to unify the geometric description of detector sensitivity, generalizing and improving previous estimators. They use it to estimate helicity sensitivity for future gravitational-wave experiments spanning twenty orders of magnitude in frequency, assuming a fully helical background with an amplitude just below current constraints.
PublicGravitational waves from the early universe might have a preferred handedness. Detecting that preference would be strong evidence that early-universe physics distinguished left from right, pointing beyond the standard account of inflation. This paper does not report such a detection. Instead, it argues that two independent kinds of wave solutions could have different or opposite handedness, making an overall measurement harder to interpret. The authors introduce a common geometric measure for comparing detectors' sensitivity to handedness and estimate the prospects for future experiments over an enormous frequency range. Those estimates assume a background with a complete handedness preference and a strength just below existing limits.
Young explorerScientists wonder whether tiny ripples from when the universe was very young could have a left-or-right preference. Two kinds of ripples might have opposite preferences, making the answer tricky. This study did not find those ripples. It worked out a way to compare how well future detectors might notice their preference, if the ripples are strong enough.
Daniel Tassie, Steven Cunnington, David Bacon+2 more
AstronomerThis simulation and forecasting study assesses MeerKLASS 21 cm intensity mapping as a probe of redshift-space distortions (RSD) and gravity over MeerKAT’s UHF range, 0.4<z<1.45. The proposed multipole-based pipeline models the HI power-spectrum quadrupole while accounting for blind foreground removal, the primary beam, and k-cuts, and uses a foreground transfer function to reconstruct the distorted signal. For 1,115 square degrees of simulated observations at 0.4<z<1.0, it yields a 6.7σ detection of an RSD-induced quadrupole relative to a quadrupole from anisotropic observational effects alone; this is not a detection in real survey data. Forecasts for the full 10,000-square-degree survey suggest that tomography, redshift-dependent models for HI bias and density, and simulation-informed priors can alleviate parameter degeneracies. Under those assumptions, MeerKLASS could achieve competitive precision on simple modified-gravity probes.
PublicThe study explores whether MeerKLASS maps of neutral hydrogen’s 21-centimetre signal could reveal how cosmic structure grows and help test gravity. The researchers used simulated observations, not actual survey measurements, to examine how foreground removal and the telescope’s response can distort the signal. Their proposed analysis recovered a statistically strong signature of redshift-space distortions in a simulated survey covering 1,115 square degrees, distinguishing it from directional patterns caused by observational effects alone. Forecasts for the larger planned survey suggest that analysing different redshift ranges together could reduce uncertainty caused by overlapping effects of hydrogen abundance and its relationship to cosmic structure. The prospects for precise gravity tests depend on the adopted models and assumptions informed by simulations.
Young explorerScientists want to use radio signals from hydrogen in space to learn how big groups of things in the universe grow and to check ideas about gravity. They practised with pretend telescope maps made on computers. Their method found a pattern they were looking for, even though the pretend telescope and other signals could make confusing patterns too. This does not mean they have found it in real telescope maps yet. Their computer tests suggest that a bigger map might help, but that depends on the ideas they use to understand the hydrogen.
Gianmassimo Tasinato
AstronomerThe authors propose cosmic acceleration as a transient phase of dark-sector relaxation rather than an approach to eternal de Sitter expansion. Guided by linear response and Onsager’s near-equilibrium regression hypothesis, they introduce a composition variable and extend constant fractional relaxation to obtain w = w0 a^(-n), with n the relaxation rate per e-fold of expansion. The resulting background history links early dark-energy suppression, an upward phantom crossing and a dark-energy density maximum to a future stationary matter-to-dark-energy density ratio, with both components ultimately diluting like pressureless matter. Fits to DESI DR2 BAO and Planck distance priors, with and without three alternative supernova compilations, yield a nominal 2.6–3.6 sigma preference for nonzero relaxation over constant w; this is not a confirmation of the proposed mechanism. A motivated linear-perturbation prescription is regular at phantom crossing and, near equilibrium, gives leading-order background-rate relaxation for regular long-wavelength composition disturbances and damped sound waves on small scales. However, the authors prove that, for separately conserved matter and dark energy, the pointwise constitutive relation cannot maintain a regular, gradient-stable negative-pressure branch throughout its full past evolution. They explore pressure-response modifications and requirements for a consistent extension beyond the near-equilibrium regime.
PublicThis paper proposes that the universe’s accelerated expansion might be temporary. In the model, matter and dark energy gradually settle into a fixed balance, eventually thinning out as the universe expands in the same way that pressureless matter does. This differs from a positive cosmological constant, which would lead to eternal accelerated expansion. Comparisons with DESI DR2 measurements, Planck distance information and alternative supernova datasets give a nominal statistical preference of 2.6–3.6 sigma for relaxation over a model with a constant dark-energy equation of state. That preference does not establish that the proposed physical explanation is correct. The authors also examine how small disturbances would behave. Their description works near equilibrium, but they prove that its original local pressure rule cannot remain both regular and stable against spatial disturbances throughout the model’s past if matter and dark energy are separately conserved. They discuss possible changes needed to make the proposal consistent over the full cosmic history.
Young explorerThe universe is getting bigger, and its growing is speeding up. These scientists suggest that the speeding up might not last forever. In their idea, matter and a mysterious thing called dark energy slowly settle into a steady balance. They compared their idea with information about the universe and found some hints in its favor, but that does not prove it is right. They also found a problem: one of their rules cannot keep little ripples behaving well all the way through the universe’s past. The idea needs more work.
Oliver H. E. Philcox
AstronomerThe authors present a complete two-loop model of the redshift-space galaxy power spectrum within the Effective Field Theory of Large Scale Structure, with 49 free coefficients accounting for fifth-order bias, redshift-space distortions, small-scale nonlinearities, spatial non-locality, bulk flows, coordinate distortions, and stochasticity. The model also encodes all deterministic contributions to the one-loop bispectrum and trispectrum and tree-level quadspectrum and pentaspectrum. Precomputing loop integrals with vegas enables millisecond likelihood evaluations. Validation against high-resolution dark-matter and realistic-galaxy simulations extends the modeled range for a luminous red galaxy sample at z = 0.5 from k_max = 0.2 to 0.34 h Mpc^-1. However, additional fifth-order biases and counterterms absorb much of the extra information, so including two-loop terms does not significantly improve constraints on sigma_8. Broader implications for cosmological inference, including joint use with higher-order statistics, remain for future work.
PublicThe researchers developed a more detailed mathematical model of how galaxies cluster, extending an existing approach to describe smaller-scale patterns where the simpler model breaks down. They tested it using high-resolution computer simulations of dark matter and realistic galaxy populations, rather than reporting a test on observed galaxy data. For one simulated galaxy sample, the new model successfully covered a wider range of clustering scales. Precomputed calculations also make it fast to evaluate how well the model fits data. But greater detail does not automatically mean sharper answers: the model has 49 adjustable coefficients, and much of the added information is absorbed by that flexibility. In these tests, estimates of sigma_8, a measure of the strength of matter clustering, did not improve significantly. Its wider benefits for measuring cosmological parameters still need investigation.
Young explorerGalaxies make patterns in space. Scientists made a more detailed math recipe to describe those patterns, even when galaxies are closer together. They tried it on galaxies made in a computer, and it worked for smaller patterns than the older recipe could handle. But the new recipe has lots of parts that can be adjusted, so it did not give a much clearer answer about how strongly matter clumps together. The scientists still need to study what else it can help them learn.
Trevor Cheung, Carlos Duaso-Pueyo, David Stefanyszyn+1 more
AstronomerThis theoretical study constructs a spin-1 field theory on an inflationary background subject to scale invariance, rotations, Bunch-Davies conditions and microcausality. The resulting Boostless Proca Lagrangian generalises massive Proca theory with five free parameters: four parity-even and one parity-odd. With three degrees of freedom imposed from the outset, microcausality requires gauge-invariant kinetic terms. Coupling the field to the inflaton yields no new bispectrum signals within this framework, supporting the authors’ interpretation of the known signals as a model-independent probe of new physics under these assumptions. The trispectrum and higher-point correlators instead acquire new shapes, with all five parameters measurable in principle. These are theoretical predictions, not reported observational detections.
PublicThe researchers develop a theory for how a particular kind of field could behave during inflation, an early period of cosmic expansion. Their theory has five adjustable parameters and must obey several consistency requirements, including a condition that prevents influences from travelling outside the light cone. They calculate how coupling this field to the field driving inflation would affect patterns involving three, four or more points. The three-point patterns contain no new signals beyond those already known under their assumptions, but four-point and more complex patterns can have new forms. In principle, those patterns could reveal all five parameters; the abstract reports theoretical work, not measurements or a discovery of this field.
Young explorerScientists used math to study how a field might leave patterns when the universe was very young and growing. Looking at three spots together gave no new kinds of patterns in their theory. Looking at four or more spots could give new kinds. These are ideas about what scientists might find, not patterns they have already seen.
Yanou Cui, Pankaj Saha, Evangelos I. Sfakianakis
AstronomerThe study investigates parametric resonance in the Abelian-Higgs model, which generates the dark-photon mass, as a mechanism for producing the relic abundance of ultralight dark-photon dark matter. Dedicated 3D lattice simulations extend earlier analytical work by capturing nonlinear effects, including backreaction and the partitioning of the relic abundance between the dark Higgs and dark photons. The authors also predict an associated stochastic gravitational-wave signal that could be accessible to a broad range of detectors. These are simulation-based findings and signal predictions, not an observational detection of dark photons or gravitational waves.
PublicUltralight dark photons are hypothetical particles that could make up dark matter. This study uses three-dimensional computer simulations to explore how they might have been produced through a resonant process in a model that also gives them mass. The simulations account for nonlinear feedback and how the remaining abundance is divided between dark photons and another component called the dark Higgs. The researchers also predict a background of gravitational waves that could be detectable by a broad range of detectors, potentially offering a way to test this dark-matter idea. The abstract reports no observational detection.
Young explorerScientists wonder if tiny, invisible particles called dark photons could be the hidden matter in space. They used a computer to explore one way these particles might be made. Their idea could also make little ripples in space called gravitational waves, which detectors might be able to find. This is a possibility they studied, not something they have seen.
Abdias Aires, Tatsuya Daniel
AstronomerThe authors calculate gravitational-wave production by a cosmological magnetic field with a narrow-band power spectrum. For magnetic power concentrated near comoving wavenumber k_c, the gravitational-wave spectrum peaks at 2k_c and has a sharp cutoff there. They apply this calculation to an ultralight-dark-matter magnetogenesis model operating around recombination, where an axion-photon coupling produces a helical magnetic field through parametric resonance. Sufficiently large coupling can bring the gravitational-wave frequency into the pulsar-timing band, but the predicted amplitude remains below experimental sensitivity for physically allowed magnetic-field energy densities. Extending the argument to other magnetogenesis epochs, they estimate T ≈ 160 MeV for a magnetic-field origin of the stochastic background suggested by pulsar timing arrays, and infer a lower bound T ≳ 1–10 MeV for viable models of this kind. These are theoretical calculations and conditional constraints, not a detection of magnetically generated gravitational waves.
PublicThis study calculates how magnetic fields in the early universe could generate gravitational waves—ripples in spacetime. If the magnetic field’s power is concentrated within a narrow range of spatial scales, the predicted wave spectrum has a sharp peak and cutoff. The authors examine a model in which ultralight dark matter helps generate a magnetic field around the time of recombination. A sufficiently strong interaction could put the waves in the frequency range studied by pulsar timing experiments, which track the timing of pulsar signals, but the calculated waves would still be too faint to detect within the allowed magnetic-field energy budget. If magnetic fields generated at another early-universe epoch caused the background suggested by pulsar timing arrays, the authors estimate a formation temperature of about 160 MeV and a minimum temperature of roughly 1–10 MeV. That possible origin remains an interpretation, not an established observation.
Young explorerMagnetic fields in the young universe might have made tiny ripples in space. The scientists used calculations to work out what those ripples could be like; they did not see them being made. In one idea involving dark matter, the ripples could be the right kind for experiments that watch the steady ticks of pulsars, but they would still be too faint to notice. The scientists also worked out how hot the young universe would need to be if magnetic fields made the ripple background that those experiments have hinted at. We do not yet know that magnetic fields made it.
X. G. Wang, A. W. Thomas
AstronomerThe study recasts existing exclusion limits on elastic spin-independent dark matter–proton cross sections as upper bounds on event rates, then uses those bounds to constrain other effective operators describing inelastic scattering of light dark matter in the GeV mass range. It considers three representative scenarios: isoscalar, proton-philic, and proton-philic spin-dependent inelastic dark matter. The abstract describes a reinterpretation of existing limits, not a detection, and provides no numerical bounds.
PublicThe researchers use existing limits on how strongly dark matter could interact with protons to calculate upper limits on how often such interactions could occur. They then apply those limits to other possible interactions in which a light dark matter particle changes its state during a collision. They examine three theoretical scenarios with different interaction properties. This is a way to constrain dark matter models using existing limits, not a report of finding dark matter.
Young explorerScientists are trying to learn how dark matter might bump into ordinary matter. They used earlier studies to work out limits on how often those bumps could happen, then used those limits to check three possible ideas about different kinds of bumps. They did not report finding dark matter.
J. D. McEwen
AstronomerThis mathematical and computational study unifies spherical convolution by lifting spin-s fields from S² to SO(3), convolving on the rotation group, and optionally projecting back through the adjoint lift to a field of spin s′. Kernel constraints, spin choices, and inclusion or omission of the lift and projection recover all previously considered rotation-equivariant convolutions. For fixed input and output spins, the authors prove that directional kernels, sphere-valued output, and rotation equivariance cannot coexist. They also connect spin fields to associated line bundles and identify the spin rotation phase with a character of the section twist. Sampling theorems support exact, efficient harmonic-space algorithms for band-limited fields, implemented in the open-source s2conv package. Numerical experiments confirm the operator reductions and equivariance to machine precision; applications to Earth and celestial-sky fields illustrate the methods rather than establish new astronomical findings.
PublicThe authors present a unified way to filter data spread over a sphere, such as maps of Earth or the sky. Their approach temporarily represents the data in a space of rotations, applies the filter there, and can then return the result to the sphere. It brings together earlier methods, including those for quantities whose values depend on orientation. The study also proves a limitation: when the input and output have fixed types of orientation dependence, a direction-sensitive filter cannot both return a spherical map and preserve the required behavior under rotations. The authors provide efficient algorithms for fields with a limited range of angular detail and release them in open-source software. Computer tests verify the expected mathematical behavior to machine precision, and Earth and sky maps demonstrate its use. This is a methods study, not a report of a new astronomical discovery.
Young explorerImagine a picture wrapped around a ball. The researchers made a way to use many different picture filters on that ball, including filters that care which way things point. Their trick is to work with the different ways the ball can turn, then bring the answer back to the ball when needed. They also proved that some things we might want a filter to do cannot all happen together. They wrote computer code and checked that it followed the turning rules extremely closely. Pictures of Earth and the sky help show how the method works.
Anderson C. M. Lai, Yurii Kvasiuk, Moritz Münchmeyer
AstronomerUsing ACT DR6 and DESI-LS DR9, the authors reconstruct velocities from the kinetic Sunyaev-Zel'dovich (kSZ) signal and estimate their cross-power with galaxy density using a novel quadratic maximum likelihood (QML) estimator in redshift-binned spherical coordinates. The cross-correlation yields a 10σ kSZ detection, with amplitude A = 0.42 ± 0.042 relative to a halo-model prediction. This lower amplitude may indicate strong feedback in massive halos, consistent with previous studies, but that interpretation is not established. Compared with a pseudo-Cℓ analysis of the same data, QML improves the signal-to-noise ratio by approximately 20%. The analysis demonstrates feasibility at the required resolution; its usefulness for upcoming high-resolution surveys is prospective.
PublicResearchers combined ACT DR6 and DESI-LS DR9 sky data to estimate cosmic motions using the kinetic Sunyaev-Zel'dovich signal and compare those estimates with the distribution of galaxies. They detected the signal with high statistical significance, at 10 sigma. Its measured strength was 0.42 ± 0.042 times a theoretical model's prediction. The weaker signal could point to strong feedback processes affecting gas in massive dark-matter halos, but this is a possible explanation rather than a confirmed cause. Their new statistical method improved the signal-to-noise ratio by about 20% over another method applied to the same data, demonstrating an approach that could benefit future surveys.
Young explorerScientists used two sets of sky information to estimate how things in space are moving. They found a clear connection between those movement clues and where galaxies are. The signal was less than half as strong as their model expected. That might mean something is changing the gas around big groups of matter, but they are not sure. Their new way of studying the information made the signal easier to pick out than the older way.
Jiaxin Han
AstronomerThis review examines the collapse physics, identification, observation, and applications of dark matter halo boundaries. The conventional picture of a monolithic, virialized halo bounded by its virial radius does not capture ongoing accretion. As accretion continues, infalling particle orbits shrink, confining newly accreted matter to a growing layer outside the virialized region. Proposed splashback and depletion radii characterize this layer from different perspectives, while the larger turnaround radius encloses the entire infall region. Together, these boundaries motivate a stratified description of halos. Theoretical models largely explain their existence, but unified, quantitative predictions of their properties remain challenging. The review discusses their potential for probing halo growth and improving structure-formation modeling, rather than reporting a new observational detection, and provides SpheriC, a Python package implementing key spherical collapse models.
PublicThis review asks where a dark matter halo—the extended structure of dark matter—really ends. The usual definition marks the edge of its settled inner region, but halos keep growing as more matter falls in. That growth creates an outer layer that the traditional boundary does not capture. Researchers have proposed different boundaries, called splashback and depletion radii, to describe this layer, while a still larger turnaround radius surrounds the whole region of infalling matter. The resulting picture is a halo with several layers rather than one simple edge. Theory can explain much of why these boundaries exist, but predicting their properties together and precisely remains difficult. Studying them could help researchers trace halo growth and better model how cosmic structures form. The authors also provide software for key spherical collapse models.
Young explorerA dark matter halo is a big gathering of matter we cannot see directly. More matter keeps falling into it, so it keeps growing. This review explains why drawing just one edge around its settled middle can miss the growing parts outside. Scientists have suggested several edges to describe those different parts, including a bigger edge around everything that is falling in. Their ideas explain a lot, but they cannot yet predict all the edges precisely. Studying these edges could help us understand how big things in space grow.
Gerasimos Kouniatalis
AstronomerThe authors propose a single minimally coupled canonical scalar field within standard general relativity to address the H0 tension, the mild preference for lower S8, and recent indications of evolving dark energy. Its smooth potential combines a localized bump with an exponential tail. In the model, the bump produces transient pre-recombination energy injection, increasing the expansion rate, reducing the sound horizon, and shifting the CMB-inferred H0 upward. A subsequent kination-like phase rapidly dilutes the field’s energy density. At low redshift, the tail produces quintessence-like evolution with w0 > -1 and wa < 0, suppressing linear structure growth and shifting S8 in the observationally preferred direction. The analysis demonstrates the proposed sequence of early enhancement, rapid dilution, and late-time thawing; the abstract does not report a quantitative observational fit establishing resolution of the anomalies.
PublicThe paper proposes one evolving field to address three puzzles: disagreement over the Universe’s expansion rate, a mild preference for less cosmic clumping, and hints that dark energy changes over time. In the model, the field briefly speeds up expansion in the early Universe, shifting the expansion rate inferred from the cosmic microwave background upward. Its energy then fades rapidly, before the field takes on a dark-energy-like role later and reduces the growth of cosmic structure. The authors show how their model can produce this sequence. This is a proposed explanation, not observational confirmation that the three puzzles are solved.
Young explorerScientists have puzzles about how fast the Universe grows and how matter gathers into clumps. This paper suggests one ingredient that changes over time: it could make the Universe grow faster early on, fade away quickly, and later help it grow while making clumps grow less. The idea has not been shown here to solve all the puzzles.
Tianyi Yang, Yan-Chuan Cai, Weiguang Cui+5 more
AstronomerThe authors search for rotational kinetic Sunyaev–Zeldovich (rkSZ) signatures of ionised gas in selected fast-rotating galaxy groups from SDSS-DR7. A clear satellite-galaxy redshift dipole in the stacked sample provides estimates of the projected angular-momentum directions, which are used to orient and stack the Planck CMB temperature map. Within the groups’ virial radii, they report a tentative 2.3-sigma rkSZ dipole detection, with a null-hypothesis probability of 0.96%, for a sample with average mass 10^14 h^-1 solar masses. They estimate average rotational velocities of approximately 100–200 km/s and report a maximum value of 158.8 ± 13.6 km/s. The results agree within uncertainties with predictions from the ELUCID constrained-realisation simulation, although the predicted rkSZ amplitude is slightly lower near the centre. A systematic bias in rotational velocities inferred from observed galaxy redshifts is identified but found to be subdominant in this analysis.
PublicResearchers looked for signs that ionised gas rotates inside groups of galaxies by examining its imprint on the cosmic microwave background, the light left over from the early universe. They first used differences in satellite galaxies’ redshifts to estimate each selected group’s rotation direction, then aligned and combined Planck microwave maps around those groups. The combined galaxy data show a clear redshift pattern, but the microwave evidence for gas rotation is only tentative, at 2.3-sigma significance. The estimated gas rotation speeds are roughly 100–200 kilometres per second. The findings are consistent, within their uncertainties, with predictions from a simulation, though its predicted microwave signal is slightly weaker near the centre. The authors also identify a bias in estimating rotation from galaxy redshifts, but find that it has a relatively small effect on this analysis.
Young explorerGroups of galaxies may have gas spinning inside them. Scientists looked for a tiny pattern that this moving gas could leave in very old light from space. They lined up pictures of many galaxy groups and put them together to help the pattern show up. They found a possible sign of spinning gas, but it is not strong enough to be sure yet. A computer model predicts something similar.
Tsutomu T. Takeuchi
AstronomerThis theoretical study formulates observer-motion responses directly at the level of cosmological pair observables, retaining arbitrary marked kernels, nonfactorizable pair inclusion, and explicit reference measures. For independent selection, the residual response is a covariance between the selection score and pair excess; a rank-one bias model reduces this to the logarithmic response of the selected mean bias. The authors demonstrate that populations with identical count-dipole coefficients and isotropic correlations can nevertheless have opposite two-point boost responses. Local division by endpoint means is not equivalent to scalar normalization of integrated pair counts, and discrete harmonic estimators require contact terms and self-pair subtraction. Exchange symmetry allows pair-midpoint anisotropy but excludes an ordinary unordered same-tracer separation dipole. The framework recovers known neighboring-multipole templates and identifies conditions for velocity–selection degeneracy and its uncertainty penalty. Finite-boost forward models independently test the response, including a nonfactorizable pair-selection case. These numerical illustrations are controlled models, not survey forecasts or observational detections. Radio and infrared catalog selections, full-pipeline response calibration, and common-velocity consistency tests are proposed as an observational route.
PublicAn observer’s motion can affect both which cosmic sources enter a catalog and how their clustering is measured. This paper develops a mathematical framework for keeping those effects separate while accounting for how pairs of sources are selected and normalized. Its models show that two populations can have the same directional imbalance in source counts and the same direction-averaged clustering, yet their pair statistics can respond oppositely to observer motion. The authors also show that different ways of normalizing pair measurements are not interchangeable. Controlled numerical models test the framework; they are not measurements of the sky or forecasts for surveys. The paper proposes future checks using radio and infrared catalogs, including calibration of the complete analysis procedure, and explains when selection effects can be confused with motion, increasing uncertainty.
Young explorerImagine counting things in the sky while you are moving. Moving can change which things make it onto your list and how pairs of them seem grouped together. The researchers made math rules to help tell these effects apart. They checked the rules with computer models, not real sky measurements. They also suggested ways to check them with sky lists later.
Md Riajul Haque, Fabio Iocco, Luca Visinelli
AstronomerThe LVK candidate S251112cm suggests at least one subsolar-mass component, potentially indicating a formation channel outside standard stellar evolution. The authors assess a two-primordial-black-hole interpretation over 0.20–1 solar masses, within the parameter space directly covered by the O4a subsolar search. They combine analytic merger-rate estimates, observational abundance constraints, and LVK search sensitivity to calculate detection probabilities for monochromatic and extended lognormal PBH mass functions. Under relaxed abundance constraints, the calculated detection probability can approach unity near the upper end of this mass range. A moderately wide lognormal distribution can enhance the probability relative to a monochromatic distribution, while a broader distribution can suppress it. The analysis finds that a PBH interpretation is compatible with current bounds even for a subdominant PBH abundance, but astrophysical uncertainties, including those affecting abundance constraints, prevent a conclusive identification. Subsolar gravitational-wave events could probe PBHs and their contribution to dark matter.
PublicA candidate gravitational-wave event, S251112cm, hints that at least one of the merging objects had less mass than the Sun. Such an object would require an explanation outside standard stellar evolution. The researchers explore whether the signal could come from two primordial black holes—black holes formed by collapsing density fluctuations in the early universe. Their calculations combine expected merger rates, limits on how common these black holes could be, and the sensitivity of gravitational-wave searches. They find that this explanation can fit current observational limits even if primordial black holes make up only a minor share of dark matter. With relaxed limits on their abundance, the calculated chance of detecting such a merger can approach certainty toward the heavier end of the studied range. That chance also depends on how their masses are distributed. These are conditional calculations, not proof of the candidate’s identity: uncertainties in the astrophysical constraints leave its nature unresolved.
Young explorerScientists found a possible ripple in space that hints two objects came together, with at least one having less mass than our Sun. They wondered whether the objects could be tiny black holes made when the universe was very young. Their calculations say that idea could fit what we know, even if there are not very many of those black holes. But some parts of the calculation are uncertain, so scientists cannot yet say that this is what really happened.
Antoine Rocher
AstronomerThe authors extend the standard Poisson satellite-occupation assumption at fixed halo mass in HOD models with a Conway-Maxwell-Poisson distribution, adding one parameter, ν, to allow sub- and super-Poisson variance. They derive analytical approximations for the expectation parameter λ and a numerical scheme connecting small- and large-λ regimes, reporting approximately 5% accuracy for 0.5 < ν < 2. Tests on HODDIES mock galaxy catalogues yield small-scale clustering deviations of up to 10% in projected clustering and 5% in the monopole and quadrupole. Counts-in-cylinders vary by up to approximately 30%, whereas the tree-level galaxy bispectrum in the Sugiyama basis changes by less than 2% up to k_max = 0.3. These modelling results, rather than observational measurements, suggest that non-Poisson satellite statistics matter for small-scale analyses but should have limited impact on cosmological constraints from large-scale power-spectrum and bispectrum measurements with k_max < 0.3.
PublicGalaxies occupy dark matter halos, and models often assume a particular statistical rule, called a Poisson distribution, for the number of satellite galaxies in halos of a given mass. This study introduces a one-parameter extension that lets those numbers fluctuate more or less than the usual rule allows. In computer-generated galaxy catalogues, changing these fluctuations alters small-scale clustering measures by up to 10%. A measure that counts galaxies inside cylindrical regions changes by about 30%, while the studied three-galaxy clustering statistic changes by less than 2% over the tested range. These are results from modelling, not observations of real galaxies. They suggest that the extra flexibility is important when studying clustering on small scales, but may have only a limited effect on estimates of cosmological parameters using large-scale clustering.
Young explorerGalaxies can live in groups inside big homes made of dark matter. Scientists use a counting rule to guess how many smaller galaxies share each home. This study tried a more flexible rule that lets the numbers vary more or less. In pretend galaxy groups made on a computer, the new rule changed some patterns of galaxies close together quite a bit, but changed one tested pattern only a little. The scientists think the rule may matter more when looking closely at galaxy groups than when looking at patterns across much bigger distances. They have not shown this with real galaxies here.
Zheng Zhang, Philip Bull, Chris Clarkson+1 more
AstronomerThis theoretical work reformulates weak lensing as a stochastic field theory of the Sachs optical scalars, driven by random Ricci-focusing and Weyl-shearing fields. Expressing convergence and shear linearly in optical-scalar fluctuations yields a path-integral, diagrammatic expansion of their n-point correlations, organised by linear response, nonlinear propagation, and driving-field cumulants. Conventional calculations are recovered in the lowest-order, linear-propagation limit. Beyond that limit, nonlinear Sachs evolution couples to non-Gaussian driving fields and mixes the matter and lensing cumulant hierarchies. The derived selection rule gives an n-point observable a direct contribution from the n-point driving cumulant, with leading hierarchy mixing from the (n+1)-point cumulant through one nonlinear Sachs interaction; higher cumulants enter at higher order. In particular, three-point focusing and shearing cumulants correct the lensing two-point function. The authors present this as a unified framework accommodating path corrections, higher-order matter statistics, stochasticity, and small-scale effects. The abstract reports a formal theoretical development, not observational measurements or numerical estimates of these corrections.
PublicMatter bends light as it travels through the universe, subtly changing how distant objects appear. This paper develops a theoretical way to calculate those changes by treating light focusing and stretching as processes driven by random fields. The usual calculation appears as the simplest limit of the new framework. Beyond that limit, the equations connect different levels of statistical information: patterns involving three focusing or stretching fluctuations can affect correlations between two lensing distortions. The authors argue that this framework can bring several complications into one calculation, including changes to light paths and small-scale effects. The abstract does not report observations or establish how large the extra effects are.
Young explorerLight from far away can bend as it passes matter, making things look a little stretched. These scientists made a new kind of maths to describe how that happens. Their maths says that different patterns of bending can work together in ways simpler maths leaves out. This is a new way to calculate things, not a report of something they saw in the sky.
J. E. Moore, C. Popik, Y. Gong+66 more
AstronomerThe study measures stacked thermal Sunyaev-Zel'dovich signals for DESI DR1 LRG- and BGS-traced groups and clusters and an optically selected eROMaPPer sample from the DESI Legacy Imaging Survey. ACT DR6+Planck Compton-y and 90, 150, and 220 GHz temperature maps are analyzed within approximately 2-arcminute disk apertures, with sources binned by luminosity, richness, or mass. In the 90 GHz map, signal-to-noise ratios exceed 38, 27, and 39 for LRG, BGS, and eROMaPPer, respectively. For LRG and BGS, dust and radio emission dominate over tSZ near and below the aperture radius; CIB contamination is less significant beyond 4 arcminutes. After mitigating contaminants, the authors combine simulated and real measurements to develop mean Compton-y–optical-depth scaling relations. Inferred optical depths agree with pairwise kinematic SZ measurements for the same tracer samples. The authors report the eROMaPPer relation as the first such relation derived directly from SZ measurements. Foreground contamination remains a central challenge.
PublicResearchers combined microwave measurements from many galaxy groups and clusters to detect their average thermal Sunyaev-Zel'dovich signal, a signature of hot gas. They obtained statistically strong detections in three samples using ACT and Planck maps. However, separating this signal from other emission remains difficult: for two samples, dust and radio sources outshine the desired signal on the small angular scales analyzed, while contamination from the cosmic infrared background is less significant on larger scales. After reducing these contaminants, the team combined observations and simulations to estimate optical depth, a measure of how readily the gas scatters light. These estimates agree with measurements using a different SZ effect. The authors also report the first relationship between the thermal SZ signal and optical depth derived directly from SZ measurements for the eROMaPPer sample.
Young explorerScientists looked at microwave light from lots of groups of galaxies together. This helped them find a strong sign of hot gas. Dust and things that give off radio waves can hide that sign, so they worked to separate them. They then used real measurements and computer simulations to estimate how much the gas scatters light. Their estimates matched another way of measuring it, but the hiding signals are still tricky.
Daniel del-Corral, Angus Spalding
AstronomerThis theoretical study examines primordial black holes (PBHs) below roughly 10^9 g that evaporate before Big Bang nucleosynthesis but can produce an early period of matter domination. The altered expansion history would imprint characteristic frequencies in a primordial gravitational-wave background, associated with the onset and end of PBH domination. The authors derive numerical relations linking these frequencies to PBH mass and, for a freely propagating background, initial PBH abundance. They argue that future gravitational-wave experiments could probe masses from roughly 10 g to the nucleosynthesis bound near 10^9 g. If the nanohertz signal reported by NANOGrav is primordial, their analysis places it in a regime probing PBH masses of 4–90 Mg. This conditional interpretation is not a detection of PBHs.
PublicTiny black holes formed in the early universe could have disappeared before the first atomic nuclei formed, making them difficult to investigate with conventional observations. This study proposes that they could still leave clues in gravitational waves from the early universe. If these black holes temporarily dominated the universe’s contents, they would change its expansion and leave distinctive features in the wave spectrum. The researchers derive ways to use those features to infer the black holes’ masses and, under an additional assumption about how the waves travel, their initial abundance. Future gravitational-wave experiments could explore a broad range of these masses. The authors also suggest that NANOGrav’s reported signal could probe black holes weighing 4–90 metric tons, but only if that signal originated in the early universe. The study does not establish that these black holes existed.
Young explorerLong ago, tiny black holes might have formed and then disappeared. Scientists think they could have changed how the young universe grew, leaving clues in ripples called gravitational waves. This study explains how those clues might tell us how heavy the black holes were. Scientists have reported some ripples, but they do not know whether those ripples came from the early universe or tell us about these tiny black holes.
D. Sanchez-Cid, J. Sanchez, I. Sevilla-Noarbe+19 more
AstronomerThe authors present the first fully photometric joint harmonic-space analysis of weak lensing and galaxy clustering using LSST-DESC pipelines on HSC Year 1 data. They measure cosmic-shear, galaxy-clustering, and galaxy–galaxy-lensing angular power spectra, perform null tests, and use mode deprojection to correct observing-condition effects on galaxy-density and shear fields. The DESC inference pipeline reproduces the official HSC Y1 cosmic-shear cosmological constraints. They constrain ΛCDM and wCDM using cosmic shear alone, clustering plus galaxy–galaxy lensing, and the full 3×2pt combination. For joint 3×2pt ΛCDM, they obtain Ω_m = 0.249 (+0.061/−0.051), σ_8 = 0.904 (+0.098/−0.091), and S_8 = σ_8√(Ω_m/0.3) = 0.821 (+0.018/−0.021). These are model-dependent cosmological constraints, not direct measurements of the parameters. HSC Y1 has imaging depth and galaxy number density similar to those expected for LSST Year 1, making this survey-data validation a foundation for the forthcoming LSST analysis.
PublicResearchers tested tools intended for LSST using existing Hyper Suprime-Cam Year 1 images, whose depth and galaxy density resemble those expected from LSST’s first year. They combined three measurements: patterns in galaxy-shape distortions caused by weak gravitational lensing, patterns in galaxy clustering, and the relationship between galaxy positions and lensing. They checked for spurious signals and corrected effects caused by observing conditions. Under the ΛCDM cosmological model, the combined measurements constrain the amount of matter and how strongly it clusters; the clustering-related parameter S_8 is 0.821, with reported uncertainties of +0.018 and −0.021. The analysis validates the tools on real survey data, but it is not yet an analysis of LSST observations.
Young explorerScientists studied pictures of faraway galaxies. They looked at where galaxies gather and how gravity gently changes the shapes we see. Using these clues together helped them learn how matter is spread through space, though their answers are not exact. They also checked tools they plan to use with future LSST pictures.
Itay M. Bloch, Salvatore Bottaro, Diego Redigolo+1 more
AstronomerThis study revises projected electroweak WIMP sensitivity in large-scale xenon detectors using a realistic detector simulation, assuming current primary noise sources can be mitigated. With present nuclear/electron-recoil discrimination, sensitivity is limited by both atmospheric-neutrino nuclear recoils and solar-neutrino electron recoils. The simulated electron-recoil contamination remains significant even when WIMP signal rates exceed atmospheric-neutrino rates, as predicted for most electroweak WIMP candidates. Updated exposure projections incorporate streamlined signal-rate and uncertainty calculations. The authors project that all real, zero-hypercharge WIMPs considered can be excluded with 50 tonne-years or discovered with 300 tonne-years, while similar exposures could probe a large portion of viable complex, non-zero-hypercharge WIMP parameter space. These are conditional sensitivity forecasts, not reported exclusions or detections.
PublicLarge xenon detectors search for hypothetical dark-matter particles called WIMPs, but neutrinos can produce events that interfere with the search. This study uses a computer simulation to estimate that interference, rather than reporting a dark-matter detection. It emphasizes that events caused by solar neutrinos remain important because detectors cannot perfectly distinguish electron recoils from nuclear recoils; atmospheric neutrinos also create a background. Assuming other major noise sources can be reduced, the authors forecast that exposures of 50 tonne-years could rule out the real, zero-hypercharge WIMP candidates studied, while 300 tonne-years could enable their discovery. Similar exposures could test many viable complex, non-zero-hypercharge candidates. These forecasts depend on the stated detector assumptions.
Young explorerScientists are looking for tiny particles that might be dark matter. Other tiny particles, called neutrinos, can leave confusing clues in their detectors. The scientists used a computer model to see how these clues could get in the way. If other detector noise can be made smaller, they predict that a big enough search could find some kinds of dark-matter particles or rule them out. They have not found them in this study.
João Gonçalves, Danny Marfatia, António P. Morais
AstronomerThe authors introduce Prominence, P, as a discriminator of gravitational-wave spectra, treating black-hole and neutron-star binaries as astrophysical backgrounds. Their analysis shows how P can distinguish spectra from first-order phase transitions, domain walls, cosmic strings, combinations of these, and other unconventional sources. Using a chi-squared statistic based on an inner product in signal space, they find that sources indistinguishable at 2 sigma using signal-to-noise ratio can be distinguished with P at significances above, and sometimes far above, 3 sigma. These are methodological findings, not reported detections of those sources. Achieving 3-sigma discrimination with pulsar timing arrays requires uncertainties in measured GW energy density at the sub-percent to percent level; LISA and ET are expected to provide sufficiently small uncertainties for P to be useful.
PublicDifferent processes in the universe can produce gravitational waves with patterns that are difficult to tell apart. This paper introduces a comparison tool called Prominence to help separate possible signals from early-universe phase changes, domain walls, cosmic strings, or mixtures of these, while treating waves from black-hole and neutron-star pairs as background. The authors' statistical analysis finds that Prominence can distinguish some signals more confidently than a signal-to-noise comparison can. This is a demonstration of a method, not a discovery of these sources. Its usefulness depends on measurement precision: pulsar timing arrays would need uncertainties of roughly one percent or less in gravitational-wave energy density. The authors expect LISA and ET data to be precise enough for the method to help.
Young explorerSpace can have tiny ripples called gravitational waves. Different things might make ripples with patterns that look alike. The scientists made a new tool called Prominence to help tell those patterns apart. Their tests suggest it can help when another way of comparing them cannot. But the measurements must be very careful. This paper does not say they have found the unusual things that might make those ripples.
Lorenzo Tranchedone, Ethan Carragher, Edward Hardy+1 more
AstronomerThis theoretical study finds that metastable cosmic strings can break early through finite-temperature effects or attachment to pre-existing monopoles during network percolation. The resulting segments may initially exceed the cosmic horizon and persist for a substantial time. Unless the strings re-percolate, early breaking typically determines the network’s eventual destruction rather than late-time quantum tunnelling. Survival to epochs probed by NANOGrav requires m_M^2/μ ≳ 10^3, with m_M the monopole mass and μ the string tension—more than an order of magnitude above previous estimates. Numerical simulations further suggest that quantum-tunnelling-induced breaking occurs predominantly at rare high-tension points, producing a much higher rate than usually assumed. The authors also briefly discuss analogous flux tubes in a dark QCD-like hidden sector whose dark-quark masses exceed the confinement scale. These are theoretical and simulation-based findings, not observations of cosmic strings.
PublicCosmic strings are hypothetical structures that could have formed in the early universe. This study argues that strings capable of breaking may do so early, either because of heat or because they attach to pre-existing objects called monopoles as their network forms. Some broken pieces could initially be larger than the cosmic horizon and survive for a long time. If the strings do not reconnect into a spanning network, this early breakage would usually cause their eventual disappearance. The calculations imply that surviving to the periods probed by NANOGrav requires a combination of monopole mass and string tension more than ten times larger than earlier estimates. Computer simulations also suggest that a separate quantum process breaks strings mainly at rare points of especially high tension, and faster than commonly assumed. The study does not report an observation of cosmic strings.
Young explorerScientists studied an idea about tiny, string-like things that might have existed in the young universe. Their work suggests that heat or getting attached to other tiny things could break these strings early. Some pieces might still last a long time. Unless the strings join into a big web again, those early breaks would usually make the web disappear later. Computer tests also suggest another way the strings could break. These are ideas scientists are testing, not strings they have seen.
Utsav Atta, Tathagata Ghosh, Sudip Manna
AstronomerThis theoretical study proposes a mechanism for annihilating domain walls in string-wall networks formed when Planck-scale gravitational effects explicitly break a global U(1) symmetry to a discrete subgroup. Such walls can eventually dominate the cosmic energy density, creating a cosmological problem strongly constrained by Big Bang Nucleosynthesis. A small bare mass for a fermion coupled to the symmetry-breaking scalar allows radiative corrections to generate a temperature-dependent vacuum bias that drives wall collapse. In the majoron example with right-handed neutrinos, the authors find that a real bare Majorana mass suffices for complete annihilation with even-dimensional gravity-induced operators. Odd-dimensional operators instead require a complex bare Majorana mass whose phase removes the residual vacuum degeneracy. These are model-based theoretical findings, not observational detections.
PublicSome particle-physics theories allow the early universe to develop boundaries called domain walls, connected to cosmic strings. If these walls persist, they could eventually dominate the universe’s energy and conflict with constraints from the formation of light elements after the Big Bang. This study proposes a way for the walls to disappear: a small mass contribution for a particle interacting with the wall-forming field can produce a temperature-dependent preference for one state over another, making the walls collapse. In a particular theoretical model involving neutrinos, the authors find that complete disappearance depends on the mathematical form of the gravity-related interactions and the mass contribution. The work presents a theoretical mechanism, not evidence that these walls have been observed.
Young explorerScientists are studying an idea in which the young universe could have had different kinds of patches, with walls between them. If those walls stayed around, they could cause trouble for how the universe grew. The scientists propose that a tiny part of a particle’s mass could help make some patches more favored than others, so the walls shrink and disappear. Their calculations say this can work in the model they studied, but they have not seen these walls in the real universe.
Dibya Chakraborty, Ahmed Rakin Kamal
AstronomerThis theoretical study examines a post-inflationary open-string Hagedorn phase in brane-antibrane inflation with perturbative volume-modulus stabilization, which avoids the standard brane-antibrane η-problem in this model class. Inflation ends through tachyon condensation and brane-antibrane annihilation, so the released energy need not immediately form an ordinary radiation bath. The analysis finds that, when the Standard Model branes share the annihilation throat, a modest energy fraction deposited into surviving visible open strings can produce a Hagedorn phase and suppress the dark-radiation contribution ΔN_eff below current observational bounds. For Standard Model branes in a separate throat, the outcome depends on inter-throat energy transfer; either prompt or delayed transfer can still produce the visible Hagedorn phase. The mechanism is most efficient when the local string scale in the Standard Model throat is lower than or comparable to that in the annihilation throat. These are conditional theoretical findings, not observations of a Hagedorn phase.
PublicThe study explores what might have happened just after the universe’s early period of rapid expansion in a particular string-theory model. In this model, inflation ends when a brane and an antibrane annihilate, releasing energy that might first enter a hot state of strings rather than ordinary radiation. The calculations suggest that this state could reduce the predicted amount of extra radiation to within current observational limits. If the strings associated with ordinary particles occupy the same region, or “throat,” as the annihilation, a modest share of the released energy can be enough. If they occupy a different throat, the outcome depends on how energy moves between the regions and on their local string scales. The study offers a theoretical possibility, not evidence that this phase actually occurred.
Young explorerScientists used a theory to ask what might have happened when the very young universe stopped growing so quickly. In their model, two things called branes meet and disappear, releasing energy. That energy might make a very hot bunch of tiny strings before becoming ordinary radiation. This could help the model predict less extra radiation. Whether it works depends on where the strings are and how the energy reaches them. Scientists have not seen this happen.
Anish Ghoshal, Pratyay Pal, Alessandro Strumia
AstronomerThis theoretical study revisits production of particles much heavier than the transition scale in ultra-relativistic bubble collisions during cosmological phase transitions. The authors argue that previous treatments based on off-shell decay of the scalar background parametrically overestimate hard production and depend on gauge choice and field-space coordinates. They propose a partonic-like formalism in which, in the ultra-relativistic limit, bubble walls undergo nearly free passage and hard particles arise through on-shell scattering among the quanta constituting the Lorentz-contracted walls. They apply the framework to heavy scalar, fermion, and vector production and examine implications for dark matter, leptogenesis, graviton production, and primordial gravitational waves. The abstract reports theoretical findings and a proposed framework, not observational detections or specific quantitative predictions for these applications.
PublicDuring changes in the state of the early universe, expanding bubbles could collide at speeds close to the speed of light and create particles much heavier than the characteristic energy scale of the change. This theoretical paper argues that an older calculation method overestimates production of these heavy particles and gives answers that depend on mathematical choices. The authors propose instead treating the collisions like high-energy particle collisions: the bubble walls pass through one another almost freely, while particles making up the compressed walls scatter and produce heavy particles. They explore possible connections to dark matter, the origin of the matter–antimatter imbalance, and gravitational waves from the early universe. These are theoretical implications, not reported observations.
Young explorerScientists are using math to study bubbles that might have formed when the universe was very young. If these bubbles bumped into each other very fast, they could make heavy particles. The scientists say an older way of counting those particles gives too many. They suggest a new way that looks at tiny bits inside the bubble walls bumping together. This is a math study, not something they watched happen.
Debadri Bhattacharjee, Pradip Kumar Chattopadhyay, Kazuharu Bamba
AstronomerMotivated by reports of possible post-merger echoes in GW170817 at 4.2σ significance and a dominant frequency near 72 Hz, this theoretical study examines strange stars with an MIT bag model equation of state in quadratic curvature gravity with non-minimal matter coupling. Such echoes are interpreted as potentially arising from gravitational perturbations partially trapped by photon spheres. In general relativity, the required compactness lies between one-third and four-ninths and is difficult to attain with realistic equations of state. Solutions of the modified Tolman-Oppenheimer-Volkoff equations yield mass-radius relations and configurations capable of supporting photon spheres and echoes. The modified Buchdahl limit allows greater compactness, but photon-sphere requirements restrict the viable parameter space. Increasing the bag constant lowers the maximum mass and echo time, shifting predicted echo frequencies toward the kHz regime; this does not establish an explanation for the reported 72 Hz signal. Echo constraints give tighter maximum mass-radius limits than hydrostatic equilibrium alone. Calculated critical impact parameters and eikonal quasi-normal modes also vary systematically with the modified-gravity parameters. The authors propose echoes, optical shadows, and quasi-normal modes as complementary probes for future detectors, including the Einstein Telescope and Cosmic Explorer; strange-star remnants remain potential, not confirmed, echo sources.
PublicSome analyses of the gravitational-wave event GW170817 have reported a possible repeating signal after the merger, but these echoes are not established here as a confirmed discovery. This study uses theoretical calculations to ask whether an unusually compact strange star could produce them under a modified theory of gravity. In the model, such a star can have a region where light can orbit and gravitational disturbances can be partly trapped, potentially creating echoes. Changing a parameter describing the star’s matter changes its maximum mass and the predicted echo frequency, with higher values pushing frequencies toward the kilohertz range rather than the reported roughly 72 Hz. The calculations also suggest that requiring echoes places tighter limits on the star’s mass and size than requiring equilibrium alone. Echoes, optical shadows, and characteristic vibrations are proposed as ways to test these models, with future gravitational-wave detectors potentially helping investigate them. The study does not confirm that GW170817 left behind a strange star.
Young explorerWhen two very tiny, heavy stars crash together, they can make ripples in space. Some scientists think they may have spotted ripples that repeat like an echo, but they are not sure. This study uses math to imagine a special kind of star that might briefly hold some ripples and let them out again. The math says this could happen in their model, but it does not prove that such a star made the possible echoes.
Mariana Carrillo González
AstronomerThis theoretical review surveys how the double copy, which relates gravitational data to gauge-theory data and is most sharply formulated through color-kinematics duality for flat-space scattering amplitudes, extends beyond asymptotically flat backgrounds. It covers curved-space constructions for boundary correlators and scattering observables in AdS, dS, and other non-trivial backgrounds; classical and field-level Kerr–Schild, Weyl, Cotton, twistor, and convolutional maps; and self-dual sectors. The emphasis is on structures inherited from flat space and obstructions introduced by curvature, rather than a claim of a universal curved-space formulation or an observational result.
PublicThis review examines a theoretical connection called the double copy, which links descriptions of gravity with those of gauge theories, another class of physical theories. The connection is clearest for calculations of scattering in flat spacetime. The review explores how it can be formulated when spacetime is curved, considering several mathematical constructions and special cases. It highlights both features that carry over from flat spacetime and obstacles caused by curvature. It surveys theoretical work rather than reporting astronomical observations or establishing that the connection works in every setting.
Young explorerScientists have a mathematical way to link two kinds of physics rules, including the rules for gravity. The link is clearest when spacetime is flat. This paper looks at ways people have tried to make the link work when spacetime is curved, too. Some pieces still fit, but the curves make other pieces harder to fit. It is a review of ideas, not a report of something newly seen in the sky.
Fu-you Zheng, Xiao-jun Gao, Hou-bing Tang+1 more
AstronomerThis study tests general relativity on kiloparsec scales using galaxy-scale strong lensing combined with Type Ia supernovae, baryon acoustic oscillations, and cosmic chronometers. To avoid circularity from assuming a GR-based cosmological model, the analysis uses the FLRW distance sum rule to constrain the post-Newtonian parameter gamma PPN and spatial curvature Omega k without selecting a particular cosmological model, while retaining the FLRW metric assumption. Its methodological additions are a second-order Chebyshev parameterization of the dark-energy evolution factor, with curvature explicitly free, and expansion from two to four probes. The joint constraints are gamma PPN = 1.119 (+0.072/-0.072) and Omega k = 0.101 (+0.077/-0.076), at 68% confidence. Gamma PPN is consistent with GR's value of 1 at 1.7 sigma; the curvature estimate favors a mildly open universe, but flatness remains consistent at 2 sigma. Relative to this benchmark, eight representative dark-energy models produce gamma PPN shifts well below the baseline 1 sigma uncertainty, indicating no significant model-induced bias at current precision rather than establishing its absence at higher precision.
PublicResearchers tested general relativity on the scale of galaxies by combining the bending of light by galaxies with three other ways of measuring cosmic distances and expansion. Their approach avoids choosing a particular cosmological model, although it still assumes a standard mathematical description of the universe's large-scale geometry. The gravity measurement is compatible with general relativity, so the study does not establish a departure from Einstein's theory. The results lean toward a mildly open universe, but a spatially flat universe remains compatible with the uncertainties. The researchers also checked eight descriptions of dark energy: each changed the gravity result by much less than its uncertainty. These comparisons suggest that choosing among those models does not significantly bias this kind of gravity test at the precision currently achieved.
Young explorerGalaxies can bend light coming from farther away. Scientists used that bent light, along with other clues about distances in space, to check Einstein's idea about gravity. Their answer still fits his idea, but the measurements are not exact enough to settle everything. They also checked whether space is flat or a little curved, and both possibilities still fit. Trying eight different ideas about dark energy changed the gravity answer only a tiny amount compared with how uncertain it is.
