78,338 papers in this slice of arXiv.
Richard M. Feder, Grigory Heaton, James J. Bock +7
We perform the first tomographic analysis of near-IR extragalactic background light (EBL) anisotropies, cross-correlating CIBER 1.1 and 1.8 μm imager data with photometric galaxy catalogs from DESI Legacy Survey DR8 and Hyper-Suprime-Cam Ultra-Deep Survey. We measure significantly higher cross-power than expectations from an integrated galaxy light (IGL) model on scales ℓ<2000
Swarna Chatterjee, Kenda Knowles
Radio megahalos are recently discovered large-scale diffuse synchrotron sources identified through LOFAR observations. We present MeerKAT L-band observations of the massive galaxy cluster RXC J0528.9−3927, that reveals faint emission surrounding its central radio halo. At 1.28 GHz, the known ∼1.14 Mpc halo is embedded within previously unreported low-surface-brightness emission extending to ∼2 Mpc. The surface-brightness profile of the emission shows a distinct flattening beyond ∼0.55R500, suggesting that the outer emission forms an additional component. These properties make the cluster a candidate megahalo system and potentially the first detected at GHz frequencies, although deeper multi-frequency observations are required for confirmation.
Fernando Izaurieta, Samuel Lepe, Cristian Quinzacara
Torsion entered early-universe cosmology twice: through the nonsingular Einstein--Cartan bounce, where the quantum spin of fermions halts the contraction, and through the proposal that the expansion following that bounce could take over the duties of cosmic inflation. We revisit the second idea in a constructive spirit. First we compute its budget: for a Weyssenhoff spin fluid with barotropic source, w∈[0,1], the accelerated window that follows the bounce spans Ne=ln[4/(1+3w)]/3(1−w)≤31ln4≃0.46 e-folds, and positive spatial curvature only shrinks it. The mechanism is sound; its torsional ``fuel'' dilutes as a−6, and the engine stops two orders of magnitude short of inflationary needs. We then ask what torsion would need in order to sustain a quasi-de Sitter phase, and give a two-branch answer in Riemann--Cartan cosmology with nonminimal couplings, where torsion is fed by the couplings rather than by spin. The vectorial branch reproduces Palatini inflation, observationally alive. On the axial branch we exhibit an exact de Sitter solution sustained by a torsion condensate: constant axial torsion f0, a linear Gauss--Bonnet coupling, and a potential fixed to V0=6f02+25v2 by the Friedmann constraint. The solution is an attractor of the homogeneous dynamics, with eigenvalue exactly −3H. The phase ends when the slope U′, a decreasing function of the roll speed at fixed flat potential, drifts down to the floor 5/16V0 and the condensate switches itself off; consistency of the effective theory pins the whole episode near the Planck scale, H≳0.3 in reduced Planck units. We studied this branch at background level; its perturbation spectrum remains open.
V. B. Díaz, D. R. G. Schleicher, M. A. Latif +1
It is sometimes suggested that the most massive quasars at high redshift may have formed from rare high-sigma peaks in the cosmic density field. We explore here the evolution in a massive primordial halo corresponding to one of these rare sigma peaks, employing cosmological high-resolution magneto-hydrodynamical zoom-in simulations with initial field strength of 10−14−10−8 G. The dark matter halo forms at the intersection of strongly convergent flows, leading to the formation of highly supersonic turbulence already on intergalactic scales, with turbulent Mach numbers of order 10−20 also within the halo. Turbulent magnetic field amplification has never been explored in this regime and we therefore investigate whether this gives rise to effects similar to those observed in more typical halos. While the weaker initial field is somewhat more strongly amplified as a result of the shear flows, overall the evolution in the different simulations is rather similar and the flows are dominated by supersonic turbulence. We show in particular that the turbulent Jeans mass always dominates over the thermal and magnetic Jeans masses, and only on scales of 10−2−10 pc, the magnetic Jeans mass may become comparable to the thermal one. Our simulations thus strongly suggest the evolution to be dominated by the large-scale dynamics. As established in previous work, we thus expect the formation of central massive objects of a few times 104 M⊙ also in the presence of magnetic fields. The situation is somewhat different from more typical atomic cooling halos, where previous results have indicated a larger relevance of the magnetic Jeans mass on intermediate scales, potentially enhancing the mass of the massive object.
Samuel McCarty, Liam Connor, Kritti Sharma +8
Understanding the distribution of cosmic baryons is crucial for advancing cosmology and galaxy formation. Localized Fast Radio Bursts (FRBs) are a promising new probe of the diffuse gas, but measurements thus far have been limited by small sample size. In this work, we measure the FRB dispersion measure (DM)-galaxy cross correlation with 130 localized FRBs, including new spectroscopic host redshifts from the DSA-110, and the DESI Legacy Survey Bright Galaxy Sample. We detect this signal at the highest significance to date (6.5σ) in both configuration and harmonic space. By comparing to simulations and a halo model, we demonstrate that this statistic can constrain the strength of baryonic feedback. Our measurements disfavor a no-feedback scenario in which gas traces the underlying dark matter at ∼9σ. In addition to small scale feedback, this represents one of the first direct measurements of the clustering of electrons on scales larger than a few Mpc. We compare our measurement to recent kinematic Sunyaev-Zeldovich effect (kSZ) studies, which show good agreement despite the differences in observational methods and sample selection. Finally, we make a first attempt at breaking the kSZ optical depth degeneracy with FRBs, jointly measuring the growth rate of large-scale structure fσ8. With future samples, FRB two-point statistics will provide precision constraints on the distribution of cosmic baryons and complement other probes.
Amirah Aljazaeri, Christian T. Byrnes
We investigate the fine-tuning of a tripartite dark matter (DM) scenario involving ultra-light primordial black holes (PBHs), whose evaporation before Big Bang Nucleosynthesis leaves Planck-mass relics and produces DM particles together with an independently produced DM component. We uniformly evaluate the parameter sensitivity required to reproduce the observed DM abundance, ΩDM. Considering thermal WIMP freeze-out, freeze-in, and QCD axion misalignment, and assuming PBHs form via collapse of perturbations following horizon entry, we find that the fine-tuning is normally dominated by the structure of the PBH relic abundance calculation rather than by the particle DM candidate or the details of PBH evaporation. In radiation-dominated cosmologies, the DM abundance is highly sensitive to the primordial curvature power spectrum because the PBH formation fraction depends exponentially on density fluctuations. Although an early PBH-dominated era dilutes pre-existing abundances and reduces the apparent tuning of the PBH abundance, inflationary fine-tuning remains required to produce the required initial large amplitude perturbations. We further examine alternative PBH formation channels, including supercooled first-order phase transitions and collapsing domain walls, and find that they replace the inflationary fine-tuning with alternative exponential sensitivities. We conclude that a natural realization of an order unity PBH relic abundance is hard to motivate.
Netra K Subramanian, Prasad Subramanian, Nimisha G Kantharia
The spectrum of a quasar consists of a few emission lines whose wavelengths are shifted by similar redshifts and numerous absorption lines whose wavelengths are shifted by different redshifts. Hence each quasar is characterised by an emission line redshift and the absorption lines redshifts are all less than the emission line redshift. The distribution of observed absorption line redshifts (zabs) with respect to emission line redshift (zem) for a large sample of quasars shows a systematic trend as pointed out by 2016arXiv160901593K. They noticed that increase in zem is accompanied by a monotonic increase in the lowest detected value of zabs and inferred that the emission and absorption lines were all formed in the quasar. This study focuses on modeling the systematic trend in the observed zem→zabs distribution. We considered the redshift data of absorption lines of singly ionized magnesium (denoted by MgII) and triply ionized carbon (denoted by CIV) for a large sample of quasars. We find that the envelope of data points defining the lowest value of the MgII absorption line redshift (which we denote by zMgIImodel) for a given zem satisfies zMgIImodel=(0.418±0.008)zem−(0.482±0.02) with an R2 value of 0.99. The model can be used to predict the lowest expected MgII absorption line redshift for any zem. We find a similar model for the lowest expected redshift of triply ionized carbon lines for any zem which is zCIVmodel=0.845(±0.0002)zem−0.153(±0.0006).
Payaswinee Arvikar, Aseem Paranjape, Saee Dhawalikar
Neutron stars (NS) are one of the indirect detection probes for dark matter (DM). The presence of DM is known to affect the observable properties of NS. Theoretical calculations for various equations of state of a DM admixed NS lead to estimates of the DM mass in a NS of the order of 10−2M⊙. On the other hand, simplistic estimates of the amount of DM that is accreted on to the NS in the Solar neighborhood, over its age, suggest that this number is of the order 10−14M⊙. Various studies have addressed this non-agreement theoretically by explaining the mechanisms leading to higher fraction than expected from smooth spherically symmetric accretion. In this work, we attempt to assess the role of the dynamic DM environmental density in the Galactic halo to explain possible enhancement in DM accretion. We consider a high resolution N-body simulation and method of Voronoi tessellation to calculate local DM density around putative NS locations in a statistically representative sample of Milky Way analogues. We infer that the dynamics of substructure may enhance the DM mass in NS by about a factor 2 as compared to the baseline, spherically symmetric expectation. Environmental effects therefore cannot explain the orders of magnitude discrepancy between equation of state and accretion based estimates of DM admixed in NS.
Zhenhao Zhang, Mingqiu Li, Sichun Sun
We discuss a mechanism for generating the baryon asymmetry in the early universe. We show that an axion-like particle can modify the related gauge field configurations in the Standard Model, thereby altering their dispersion relations. This change in the Chern-Simons number can source a violation of baryon number. We derive the relationship between the resulting baryon number and the evolution of the axion background. We estimate the baryon asymmetry produced via this mechanism and show that the observed value can be naturally achieved. We also show that axion photon coupling produces Cosmic Microwave Background spectral distortion. Our results show that the resulting distortion approaches a constant at low frequencies, unlike the conventional y-type and μ-type distortions.
Marcos H. Cruz, Miguel Cruz, Joel Saavedra +1
The growing number of generalized horizon entropy proposals has led to a wide variety of modified cosmological models, yet there is currently no general physical principle capable of discriminating among them. We show that the generalized second law (GSL) of thermodynamics provides such a criterion. Considering a general modified Friedmann framework described by an arbitrary function f(H) of the Hubble parameter, and allowing the apparent horizon and the cosmic fluid to evolve out of thermal equilibrium, we derive model-independent constraints on the asymptotic scaling of the horizon entropy, SA∝Ak. We find that phantom evolution requires k≥(3ω−1)/(2ω), with ω the total fluid equation of state, whereas quintessence imposes the complementary upper bound. Additionally, in the exact thermal equilibrium limit, the dynamical coupling strictly enforces k≤2, recovering the non-equilibrium quintessence bound. The two bounds converge to the unique value k=2 as the phantom divide is approached, indicating that a smooth crossing of the phantom divide is thermodynamically associated with a quadratic entropy-area scaling, where the effective theory degenerates into a logarithmic gravity framework. Applying this criterion to representative generalized entropy models shows that many commonly used proposals are constrained by the generalized second law, whereas multiparameter constructions are naturally compatible with the required asymptotic behavior. Finally, we demonstrate that the same thermodynamic selection principle extends to derivative-dependent cosmologies described by f(H,H˙), highlighting its robustness beyond entropy functionals that depend only on the horizon area.
Mawson W. Sammons, Airene Ahuja, Matt Dobbs +25
Massive galaxy clusters can introduce gravitational lensing and populations of suppressed star formation member galaxies into the line of sight, potentially changing the distribution of observable sources toward them from that of the average sky. As a result, Fast Radio Bursts (FRBs) aligned with galaxy clusters can provide a unique window into parameter spaces of the FRB population that other lines of sight do not afford. In this study, we demonstrate that the second CHIME/FRB baseband catalog contains FRBs emitted from within or behind clusters identified from the latest DECaLS data release; we isolate a sample of 26 FRBs where this is likely, including one repeating FRB and two FRBs that intersect the Coma cluster. Comparing our results against a range of simulated FRB populations, we conclude that the number of these associations represents a 3σ rate enhancement toward galaxy clusters, constituting 1.4±0.4% of the FRBs detected in the second CHIME/FRB baseband catalog. We suggest that this enhancement is caused by an equal proportion of member galaxies hosting additional FRBs, and gravitational lensing magnifying background sources. We demonstrate that such contributions are sensitive to alternative progenitor channels and high redshift evolution in the FRB population, providing a future avenue for constraining these features. Considering the redshifts and masses of the associated clusters, we identify FRB 20211113A, which is aligned with the strong gravitational lens Abell 2218 as a potential lensed candidate for further consideration.
Raquel R. Valença, Lilianne Nakazono, Rafael Izbicki +6
We assess whether tabular foundation models can be used as off-the-shelf probabilistic photometric-redshift estimators for quasars in the 12-band S-PLUS DR6 survey, where colour-redshift degeneracies produce multi-modal posteriors and spectroscopic training sets are shifted relative to the photometric population. TabPFN 2.5, RealTabPFN 2.5, and TabICL are benchmarked against eight task-specific baselines, including linear conditional Gaussians, FlexZBoost, mixture-density networks, normalising flows, random forests, and gradient-boosted trees, with training sets from 500 to 121,626 quasars, using both density and point-prediction metrics, together with importance-weighted scores that approximate deployment on the photometric target sample. TabPFN 2.5 is best or statistically tied for best on all metrics except the unweighted CDE loss, on which the normalising flow is statistically tied and attains the lowest mean value; its largest gains occur for small training sets and in difficult regimes (very bright and faint sources, high redshift), while retaining near-nominal calibration under covariate shift. Its main practical cost is inference: with frozen weights, large support and target catalogues require substantial GPU/accelerator memory, and full-catalogue deployment may need support-set subsampling or distillation. SHAP attributions identify WISE W1/W2 as the strongest individual predictors, with UV and optical bands offering non-negligible refinements. We conclude that TabPFN 2.5 is a strong default for probabilistic quasar photo-z estimation, particularly when training data are limited or when calibration under covariate shift is critical.
Krzysztof Lisiecki, Nicola Principi Cavaterra, Agnieszka Pollo +9
Measuring the expansion rate of the Universe is a central challenge in cosmology. Independent and robust methods are essential to validate existing measurements and assess potential systematic effects. We employ the cosmic chronometer (CC) approach, which uses the differential age evolution of quiescent galaxies to measure the Hubble parameter H(z) without assuming an underlying cosmological model. In contrast to previous CC studies, we restrict our analysis to relics -- ultra compact massive galaxies (UCMGs) hosting the oldest stellar populations -- thereby minimising uncertainties related to star formation history and merger history. We select a sample of 189 relic galaxies in the redshift range 0.07< z <0.22 from the E-INSPIRE UCMGs catalogue. Using the D_n4000 spectral index of relic galaxies and its redshift evolution, combined with MILES stellar population synthesis models, we derive the differential age relation required to infer H(z). We account not only for metallicity effects but also for the impact of alpha-element enhancement, which has not been explicitly propagated into the systematic uncertainty budget of the D_n4000 cosmic chronometer method. We obtain an independent measurement of H(z=0.15) = 85±53 km/s/Mpc. The total uncertainty is dominated by statistical limitations. The systematic component is 13% (8.7% when alpha-enrichment is not propagated), among the tightest estimates in current CC studies. We find that alpha-enrichment plays a major role in the systematic error budget, particularly in the high metallicity regime, and must be properly accounted for in future analyses. We demonstrate the proof of concept that relic galaxies provide a promising pathway to reduce systematic uncertainties in the CC method. The statistical uncertainties, which dominate the error budget, can be significantly reduced by the increase of data volume expected during the next years.
Julian Heeck, Yu Zhi
Neutron stars have baryon chemical potentials that can exceed the neutron mass, providing favorable conditions to convert neutrons to new particles carrying baryon number, even if those processes are kinematically forbidden in vacuum. We study the effect of GeV-scale scalars with baryon number on neutron stars' equation of state and show that non-perturbatively large repulsive self-couplings are required to support the observed two-solar-mass neutron stars. We also study potentials with attractive self-interactions, which can trigger scalar production even for masses above the chemical potential and resemble Coleman's Q-matter.
T. Toghrai, A. Daassou, Y. Ouchhaine +2
Primordial black holes (PBHs) form through several distinct mechanisms, each imprinting a characteristic mass function that a single-mass treatment risks erasing. Building on the FRISBHEE code, we introduce FRISHBEE, implementing four mass functions--log-normal, power-law, critical collapse, metric preheating--in a multimodal framework, with spin modeled via Gaussian and Fishbach profiles. Crucially, each channel's weight is derived from the primordial collapse probability rather than fitted, tying the mass function to the power-spectrum amplitude--a link between inflationary model-building and CMB observables. Solving the Friedmann-Boltzmann equations for MPBHin=107 g in the pre-BBN window, we compute ΔNeff for five distributions, three spin configurations, and three weightings. Extended mass functions enhance ΔNeff over the monochromatic benchmark by factors of ∼1.03 (critical collapse) to ∼1.84 (log-normal), preserving the hierarchy LN>MM>PL>MP>CC across the mass window {105,107,108} g. Near-extremal spin (a⋆=0.99) and spin-2 dark radiation invert this trend: superradiant spin loss averages away faster in broad distributions than in a monochromatic population, letting the monochromatic approximation overestimate ΔNeff. Against CMB-S4 and Simons Observatory sensitivities (σ≃0.06 and 0.05), the monochromatic benchmark is undetectable for scalar dark radiation (sDR =0), while log-normal, power-law, and multimodal distributions reach ∼1.6--1.7σ; for spin-2 dark radiation the signal drops over an order of magnitude, with none detectable. The formation channel thus governs the magnitude and observational accessibility of the Hawking signal, establishing ΔNeff as a discriminant between single- and multi-channel PBH formation scenarios.
Kensuke Akita, Maksym Ovchynnikov, Vsevolod Syvolap
Hadronically decaying particles with lifetimes τ≳0.02s are excluded by Big Bang Nucleosynthesis almost independently of their abundance: the mesons from their decays convert protons into neutrons faster than the reverse, and helium is overproduced. For heavy neutral leptons (HNLs), this blankets the couplings the upcoming accelerator searches can reach. We propose a scenario with large lepton flavor asymmetries in which HNLs evade it. A Dirac HNL decays into π+ and its antiparticle into π−, so an asymmetry between the two populations injects an excess of π+, which converts the neutrons back to their standard abundance, while a cancellation between the asymmetries and the HNL decays keeps the shift in Neff small. This opens the parameter space with ml+mπ≲mN≲1GeV and τN≲1s, including a substantial region within the reach of SHiP. A discovery there, combined with the BBN and CMB observables, would fix the primordial flavor asymmetries up to one remaining direction. The relic neutrino background and a possibly first-order cosmic QCD transition, a source of gravitational waves, may probe that direction, and with it the lepton asymmetry of the Universe.
Dionysios P. Theodosopoulos, Katherine Freese, Chris Kelso +1
Paleo-detectors record and retain crystal damage in ancient minerals from nuclear recoils induced by dark matter scattering over geological timescales. Previous studies have shown that paleo-detectors can provide sensitivity to a variety of dark matter (DM) scenarios which is complementary to conventional direct-detection experiments. In this paper, we complete the first detailed study of how well paleo-detectors can reconstruct DM parameters or distinguish between different types of DM interactions with nuclei in the presence of a DM signal, considering both elastic and inelastic DM-nucleus scattering. For representative nuclear recoil track read-out scenarios, we demonstrate that weakly interacting massive particle (WIMP) DM masses can be reconstructed for a variety of Non-Relativistic Effective Field Theory (NREFT) interactions between WIMPs and nuclei. In particular, paleo-detectors are projected to be capable of reconstructing WIMP masses ≲ 10 GeV, a regime that is challenging for conventional direct-detection experiments; further, we find that paleo-detectors could reconstruct WIMP masses up to 1 TeV for hypothetical signals within their accessible parameter space, extending the mass range over which reconstruction is possible by up to a factor of ∼2 compared with analogous studies of conventional direct-detection experiments. In addition, we demonstrate that paleo-detectors could discriminate between canonical spin-independent or spin-dependent NREFT interactions and non-canonical interactions which can depend on the relative velocity or momentum transferred between the WIMP and nucleus. Specifically, at WIMP masses ≳ 10 GeV, we project that canonical NREFT interactions can be excluded by paleo-detectors in the cases of nearly all non-canonical interactions without measurement of nuclear recoil direction, which conventional experiments typically require.
J. Choppin de Janvry, C. Yèche, Arjun Dey +55
Some of the next steps for high-precision cosmology lie within the high-redshift, high-density universe. Spectroscopic survey experiments such as the Dark Energy Spectroscopic Instrument (DESI)'s second phase DESI Run 2 will shift towards probing Lyman Break Galaxy (LBG) populations from z∼2 to z∼4.5. For this faint sample, spectroscopic redshift measurement and sample decontamination remains a challenge, even after target selection. We propose an approach based on supervised weighted contrastive learning, in order to both learn a redshift representation for spectra and decontaminate the sample from quasars and low redshift emission line galaxies. This strategy generalizes the contrastive learning loss approach with continuous relationship weights, such that the network simultaneously learns redshift and classification tasks. The model shows stronger outlier classification and comparable redshift identification performances when compared to the previous network used for DESI (a modified version of QuasarNET) on the same dataset. In particular, contrastive learning is well suited to the small, visually-inspected sample used for training and testing, especially given the multi-task nature of this work.
Andres Escala
We explore the possibility of a Machian interpretation for the phenomena associated with asymptotically flat rotation curves in disk galaxies, providing an alternative to both the Lambda-Cold Dark Matter (ΛCDM) paradigm and MOdified Newtonian Dynamics (MOND). We argue that the MOND acceleration scale a0 is likely not a new fundamental constant, but rather a manifestation of the cosmological scales of the observable Universe (a0∼c2/Ru∼c4/GMu∼c/tu). We rewrite the Baryonic Tully-Fisher Relation (BTFR) in a cosmological format, MuMbar=(cV)4, suggesting that the transition to the non-Newtonian regime occurs when local accelerations become small enough to feel the global cosmic boundary, and showing that any Machian interpretation must fulfill a relation of this form. Furthermore, this framework naturally predicts a cosmological evolution of the BTFR normalization as the mass in the observable Universe evolves. We test these predictions against recent high-redshift observations (z∼2 and z∼5), finding that the data favor a flat, baryon-only, Λ-dominated quasi-de Sitter universe (Ωm≈0.05, ΩΛ≈0.95) over standard MOND or ΛCDM parameters. These results suggest that flat galactic rotation curves may be interpreted as compelling evidence in favor of Mach's Principle, in at least some of its versions.
Hanjue Zhu
I introduce the last crossing of the photon-counting barrier as a statistic for analytical models of cosmic reionization. Because ionizing galaxies are biased tracers of density and their photons propagate through gas of spatially varying opacity, the galaxy-IGM connection requires statistics beyond the global ionized fraction. The excursion-set model of Furlanetto et al. (2004) identifies the ionized-bubble scale around a point with the first crossing of a photon-counting barrier. I develop the last-crossing formalism and define the last-crossing scale, Rℓ, as the smallest scale on which the enclosed photon budget still ionizes the enclosed gas. I derive its distribution analytically. Using the empirical-barrier framework of Kaurov (2016) applied to CROC simulations, I measure both crossings in the simulated IGM. The last-crossing formalism separates externally ionized regions, whose photon-counting condition fails below Rℓ, from internally ionized regions whose trajectories remain above the barrier to the resolution scale. Resolved external regions are predominantly underdense, with larger Rℓ selecting lower density and later reionization. At fixed local density, first-crossing scale, and reionization redshift, these regions show deficits in ionizing-luminosity and galaxy-number density at small radius relative to matched unresolved regions, and excesses in both at intermediate radius. Their combination of low gas density and a deficit of nearby sources suggests that Lyα transmission spikes may preferentially arise in these regions: low density reduces the opacity, while sources on larger scales maintain the ionized state. The last-crossing picture connects the internal source geometry of ionized regions to a testable prediction for radial galaxy distributions around transmission-selected IGM locations.