Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.IM
Tabular foundation models for the estimation of probabilistic quasar photometric redshifts in S-PLUS
Raquel R. Valença, Lilianne Nakazono, Rafael Izbicki et al. (+6 more)
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.
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All authors Raquel R. Valença, Lilianne Nakazono, Rafael Izbicki, Marco Henrique de Almeida Inácio, Bruno Marcondes e Resende, Maycon Jorge Deláqua da Silva, Kiana Coimbra Buin Lins, Natanael M. Cardoso, Claudia Mendes de Oliveira
Cosmology and Nongalactic Astrophysics
CORN – Chronometers of Relic Nature I: The first estimate of the expansion rate of the Universe using compact relic galaxies
Krzysztof Lisiecki, Nicola Principi Cavaterra, Agnieszka Pollo et al. (+9 more)
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\pm53 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.
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All authors Krzysztof Lisiecki, Nicola Principi Cavaterra, Agnieszka Pollo, Chiara Spiniello, Laura Hunt, Charlie Rosen, Marek Biesiada, Darko Donevski, Patryk Matera, Giuliano Lorenzon, Katarzyna Małek, John Mills
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Julian Heeck and 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.
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Cosmology and Nongalactic Astrophysics
Evaporation of Primordial Black Holes with Multimodal Mass and Extended Spin Distributions: Cosmological Imprints on the Effective Number of Relativistic Species
T. Toghrai, A. Daassou, Y. Ouchhaine et al. (+2 more)
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 $M_{\rm PBH}^{\rm in}=10^{7}$~g in the pre-BBN window, we compute $\Delta N_{\rm eff}$ for five distributions, three
spin configurations, and three weightings. Extended mass functions enhance $\Delta N_{\rm eff}$ over the monochromatic
benchmark by factors of $\sim\!1.03$ (critical collapse) to $\sim\!1.84$ (log-normal), preserving the hierarchy $LN > MM > PL > MP > CC$ across the mass window $\{10^{5},10^{7},10^{8}\}$~g. Near-extremal
spin ($a_{\star}=0.99$) 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 $\Delta N_{\rm eff}$. Against CMB-S4 and Simons Observatory sensitivities ($\sigma\simeq 0.06$ and $0.05$), the monochromatic
benchmark is undetectable for scalar dark radiation (sDR $=0$), while log-normal, power-law, and
multimodal distributions reach $\sim\!1.6$–$1.7\sigma$; 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 $\Delta N_{\rm eff}$ as a discriminant between single- and multi-channel PBH formation scenarios.
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All authors T. Toghrai, A. Daassou, Y. Ouchhaine, H. Laassiri, R. Benbrik
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Heavy neutral leptons beyond the BBN bound: probing the lepton asymmetry of the Universe
Kensuke Akita, Maksym Ovchynnikov and Vsevolod Syvolap
Hadronically decaying particles with lifetimes $\tau\gtrsim0.02\,{\rm s}$ 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 $\pi^+$ and its antiparticle into $\pi^-$, so an asymmetry between the two populations injects an excess of $\pi^+$, which converts the
neutrons back to their standard abundance, while a cancellation between the asymmetries and the HNL decays keeps the shift in $N_{\rm eff}$ small. This opens the parameter space with $m_l+m_\pi\lesssim m_N\lesssim1\,{\rm GeV}$ and $\tau_N\lesssim1\,{\rm s}$, 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.
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Cosmology and Nongalactic Astrophysics
Reconstructing Dark Matter Mass and Discriminating Standard and Non-Standard WIMP-Nucleus Interactions with Paleo-Detectors
Dionysios P. Theodosopoulos, Katherine Freese, Chris Kelso et al. (+1 more)
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 $\lesssim$ 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 $\sim 2$ 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 $\gtrsim$ 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.
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All authors Dionysios P. Theodosopoulos, Katherine Freese, Chris Kelso, Patrick Stengel
Cosmology and Nongalactic Astrophysics
Lyman Break Galaxy selection and redshift measurement with supervised contrastive learning
J. Choppin de Janvry, C. Yèche, Arjun Dey et al. (+55 more)
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$\sim$2 to z$\sim$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.
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All authors J. Choppin de Janvry, C. Yèche, Arjun Dey, C. Magneville, C. Payerne, J. Aguilar, S. Ahlen, E. Armengaud, S. Bailey, F. Beutler, D. Bianchi, D. Brooks, A. Carnero Rosell, E. Chaussidon, T. Claybaugh, A. Cuceu, K. S. Dawson, A. de la Macorra, A. de Mattia, P. Doel, A. Font-Ribera, J. E. Forero-Romero, E. Gaztañaga, Satya Gontcho A Gontcho, G. Gutierrez, H. K. Herrera-Alcantar, K. Honscheid, M. Ishak, S. Juneau, T. Karim, D. Kirkby, A. Kremin, A. Lambert, M. Landriau, L. Le Guillou, M. Manera, A. Meisner, R. Miquel, S. Nadathur, G. Niz, E. Paillas, N. Palanque-Delabrouille, W. J. Percival, F. Prada, I. Pérez-Ràfols, C. Ravoux, G. Rossi, R. Ruggeri, E. Sanchez, C. Saulder, D. Schlegel, M. Schubnell, H. Seo, J. Silber, M. Siudek, G. Tarlé, B. A. Weaver, H. Zou
Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
Flat Galactic Rotation Curves Interpreted as Evidence for the Mach's Principle
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 ($\Lambda$CDM) paradigm and MOdified Newtonian Dynamics (MOND). We argue that the MOND acceleration scale $a_0$ is likely not a new fundamental constant, but rather a manifestation of the cosmological scales of the observable Universe ($a_0 \sim c^2/R_u \sim c^4/GM_u \sim c/t_u$). We rewrite the Baryonic Tully-Fisher Relation (BTFR) in a cosmological format, $\frac{M_{\rm bar}}{M_{u}} = \left( \frac{V}{c} \right)^4$, 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 ($z \sim 2$ and $z \sim 5$), finding that the data favor a flat, baryon-only, $\Lambda$-dominated quasi-de Sitter universe ($\Omega_m \approx 0.05$, $\Omega_\Lambda \approx 0.95$) over standard MOND or $\Lambda$CDM 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.
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Cosmology and Nongalactic Astrophysics
The Last Crossing in Excursion-Set Theory of Cosmic Reionization
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, $R_\ell$, 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 $R_\ell$, from internally ionized regions whose trajectories remain above the barrier to the resolution scale. Resolved external regions are predominantly underdense, with larger $R_\ell$ 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 Ly$\alpha$ 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.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Mysterious Transients in the Palomar Observatory Sky Survey (POSS-1) as profound manifestation of the Dark Matter physics
Ariel Zhitnitsky
Transient
star-like objects of unknown origin have been identified in the first Palomar Observatory Sky Survey (POSS-1) as part of the Vanishing and Appearing Sources during a Century of Observations (VASCO) project. The source of the transients recorded by POSS-1 remains unknown, which is the warrant to coin the observed phenomena as Mysterious Transients (MT). We advocate an idea that the dark matter (DM) in form of the
axion quark nuggets (AQN) made of standard model
quarks (or antiquarks) and gluons, similar to the old idea of the Witten's strangelets, could simultaneously explain all the observed MT signals (including very short time scale for flash itself, association with nuclear test timing, observed
alignments of several MT events, correlation with UAP reports, etc) collected or recorded for many years. Essentially we argue that the MT is a cousin of Ball Lightning (BL) events, also observed for centuries, without commonly accepted physics explanation. The basic parameters of this model (such as the typical baryon charge of the nuggets) had been fixed long ago by explaining the observed excess of radiation at variety of scales: from galactic to the solar, to local Earth's environments. In this work we use the same framework with the same set of parameters to study the observed MT phenomena. We also suggest several tests which substantiate or refute our proposal. We also present some suggestions on type of instruments required to study this specific (and well defined) type of the UAP events representing the cousins of BL and MT events in the AQN framework.
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Cosmology and Nongalactic Astrophysics
Realization Variance of Gravitational Wave Background Anisotropies from Shot Noise for Pulsar Timing Arrays
Meng-Xiang Lin, Adam Lidz and Chung-Pei Ma
Shot-noise anisotropies in the nHz gravitational wave background (GWB) are a promising target for
pulsar timing arrays (PTAs). If the nHz GWB is sourced by merging supermassive black hole binaries (SMBHBs), as current evidence suggests, the shot-noise signal is expected to be large, potentially of order unity at observing frequencies of $f \sim 1 \, \mathrm{yr}^{-1}$. In this regime, the signal is dominated by rare bright binaries, and Poisson fluctuations in the discrete SMBHB population produce significant spatial anisotropies. Here, we use Monte Carlo simulations to model the realization-to-realization scatter in the shot-noise, sampling from empirically calibrated models of the SMBHB source populations. We find that the probability distribution of shot-noise amplitudes is broad, spanning a factor of $\sim 50$ (95% interval) at fixed frequency, with a long tail towards high amplitudes. The most probable and median amplitudes lie significantly below the ensemble means by factors of $\sim 2-3$, implying that the shot-noise in typical realizations is smaller than the mean. The ensemble-averaged shot-noise also differs from simple estimates based on moments of the strain, $\langle h^4 \rangle/\langle h^2 \rangle^2$, because the average of a ratio is not equal to the ratio of the averages (i.e., $\langle X/Y \rangle \ne \langle X \rangle/\langle Y \rangle$). This difference is a factor of $\sim 3$ at $f = 0.1 \, \rm{yr}^{-1}$, growing to larger than two orders of magnitude by $f \sim 1 \, \rm{yr}^{-1}$, where the GWB is dominated by low abundance, high-strain sources. Shot-noise nevertheless provides a powerful diagnostic for understanding the GWB and SMBHB populations; interpreting PTA measurements, however, requires modeling its full probability distribution.
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Cosmology and Nongalactic Astrophysics
The Fate of Large Scale White Noise in Second-Order Cosmological Perturbation Theory
Aurora Ireland
Working to second order in cosmological perturbation theory, we reconsider the Large Scale White Noise (LSWN) effect proposed in [2511.13866] and [2511.15803]. We demonstrate that the kurvature density variable $\Delta \rho$ does indeed develop LSWN at second order. However, contrary to the claims of [2511.15803], we show that this is not inherited as an infrared (IR) pole in the second-order comoving
curvature perturbation $R_2$. This apparent enhancement was an artifact of using a linear Poisson equation to relate two genuinely second order quantities. Further, we show that $R_2$ is protected from developing any such IR enhancement: $\lim_{k \rightarrow 0} \left( k^2 R_2 \right) = 0$, which follows from a conservation law in the soft limit. The constraint proposed in [2511.15803] and its implications for the small-scale primordial power spectrum are therefore invalid.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Thermal Origin of Black Hole Quasinormal Modes
D. Giataganas, G.F. Giudice, A. Kehagias et al. (+2 more)
When a black hole rings after a merger, it emits gravitational waves at characteristic frequencies known as quasinormal modes (QNMs). In the eikonal limit, these modes are governed by the unstable circular light orbits that form the
photon ring. In this work, we demonstrate that the ringing of a black hole has a precise thermal interpretation. A probe string propagating in the near-ring geometry acquires an induced Rindler horizon on its worldsheet, with a temperature set by the Lyapunov exponent of the
photon ring. Out of this structure, the black hole QNMs emerge as thermal excitations, so that the characteristic ringing of a black hole is the retarded response of a thermal system living on the
photon ring. We explicitly derive the QNM spectrum from two complementary perspectives: microscopically, via unstable transverse worldsheet fluctuations, and macroscopically, through the pole structure of the causal response function of an open thermal
quantum system.
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All authors D. Giataganas, G.F. Giudice, A. Kehagias, F. Quevedo, A. Riotto
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Adiabatic Perturbations in GW170817-Compatible Einstein-Gauss-Bonnet Inflation
S.D. Odintsov and V.K. Oikonomou
We study the adiabaticity of the cosmological perturbations in the context of inflationary Einstein-Gauss-Bonnet theories. We focus on viable inflationary Einstein-Gauss-Bonnet theories which are compatible with the current
Cosmic Microwave Background radiation experiments and also are compatible with the GW170817 observations. We derive the effects of the adiabaticity requirement on the Einstein-Gauss-Bonnet physical parameters and we show that the sound speed of the scalar perturbations and the propagation speed of the tensor perturbations are constrained. We consider two classes of inflationary viable and GW170817-compatible theories, and in the first class the adiabaticity is not violated during inflation, while in the second class the adiabaticity is violated only at the end of inflation. We discuss the effects of the adiabaticity violation in the second class of models. From our analysis, it seems that only one class of viable EGB inflationary theories, which is also compatible with the GW170817 event, is free from adiabaticity pathologies.
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Cosmology and Nongalactic Astrophysics
Not R Kurvature: Beating Large-Scale White Noise
Wayne Hu
Kurvature, a recently identified
curvature invariant, has been argued to acquire superhorizon, or large-scale, white noise from hard-hard momentum coupling even when matter nonlinearities are small. If kurvature were related directly to cosmological
curvature perturbations R through a Poisson equation, this white noise would cause an infrared-divergent variance sensitive to ultraviolet hard-mode physics. However, this relation does not generically hold. Kurvature is not intrinsic 3-
curvature: on comoving slices it contains extrinsic-
curvature terms, and intrinsic
curvature is not related to R by a Poisson equation beyond linear order. We test this inference with second-order perturbation theory in radiation domination, relevant to CMB observables. Quadratic hard-hard composites do generate large-scale white noise in the kurvature density, but the
Hamiltonian constraint separates it into intrinsic
curvature and extrinsic shear, or equivalently density and expansion. Only the extrinsic terms carry the growing dimensionless kurvature density that mimics an ordinary density fluctuation above the horizon. The direct hard-hard
curvature power is ultraviolet convergent, dominated by horizon-scale modes at evaluation, and leaves no IR relic in R from purely ultraviolet modes. By contrast, the Poisson construction of a
curvature potential from kurvature is infrared divergent and cutoff sensitive; its white noise arises from extrinsic
curvature associated with nonlinear acoustic beat modes in a radiation fluid.
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Cosmology and Nongalactic Astrophysics
Cross-frequency SGWB anisotropy from compact topology: CMB B-mode covariance as a transfer probe
Li-E Qiang and Peng Xu
Compact spatial
topology restricts the eigenmodes of primordial tensor perturbations, and the resulting discreteness can render the primordial
stochastic gravitational-wave background (SGWB) anisotropic. Here we treat the CMB tensor $B$-mode covariance as a transfer-filtered measurement of that ultra-low-frequency anisotropy. Writing the normalized angular tensor-power measure as $F(k,\hat k)=1+Q(k,\hat k)$ and its nonmonopole moments as $q_{LM}(k)$, we obtain an explicit kernel that maps $q_{LM}(k)$ onto the off-diagonal covariance $\delta C^{BB}_{\ell m,\ell' m'}$. The kernel factorizes into tensor transfer functions and a
spin-weighted Gaunt coefficient and obeys the parity rule $L+\ell+\ell'$ even for $BB$ and odd for $TB/EB$. It is an exact source–response representation of the full compact covariance rather than an additional observable. For a cubic three-
torus the geometry pins down a common cubic angular subspace and orientation across frequency bands, although the amplitudes of the allowed multipoles still depend on the radial shell and source spectrum. The same
topology-restricted template can therefore be read out either through the CMB $B$-mode kernel or through the anisotropy response of PTA/LISA/Taiji/TianQin searches. Using CAMB transfer functions and an invariant anisotropic-template statistic, we contrast this tensor channel with the scalar $T/E$ covariance. Independent direct angular-shell sums and $q_{LM}$–Gaunt contractions agree at $L_q^{\max}=2\ell_{\max}$ to relative Frobenius residuals of $1.4\times10^{-14}$–$3.0\times10^{-14}$. The scalar sector holds most of the practical CMB
topology information; a fixed-template scan places the combined full-sky $S/N=1$ transition between $L/\chi_*=2.34$ and $2.36$, while the $B$-mode channel remains subthreshold but isolates the primordial SGWB contribution.
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Cosmology and Nongalactic Astrophysics
CMB Spectral Distortion Anisotropies from Acoustic Damping with primordial non-Gaussianity
Jens Chluba, Atsuhisa Ota and Nicola Bartolo
In this paper, we evaluate the precise distortion source and transfer functions caused by mixing of blackbodies of different temperatures using the recently developed frequency hierarchy (FH) treatment of CosmoTherm. With this we are able to evaluate the effects of primordial non-Gaussianity (PNG) on the $\mu T$, $\mu E$, $y T$ and $y E$ cross-power spectra including the coupled spectro-spatial
evolution and important
photon-transport effects retained by the FH treatment. For local-type PNG, we compare our results with those from previous works, illustrating new aspects that were previously not captured. We then demonstrate how the $\mu T$ and $\mu E$ signals change in the presence of enhanced
curvature perturbations at small scales. For a nearly scale-invariant primordial spectrum, our results agree broadly with previous estimates on large angular scales but exhibit additional small-scale damping and modified $y$-distortion correlations arising from the scale dependence of the heating source and the distinct transport of distortion perturbations. Tight-coupling and monopole-source approximations accurately reproduce the $\mu$-distortion spectra, while the $y$-distortion signals remain more sensitive to the detailed source
evolution. For enhanced small-scale power, anisotropies generated by propagation of the distorted average spectrum can become comparable to those from anisotropic dissipation. Their different angular dependences and parameter scalings principally allow the small-scale power amplitude and primordial non-Gaussianity to be constrained separately. The results presented here thus pave the path for studying PNG in new regimes using existing and upcoming high precision CMB anisotropy data to measure primordial distortion correlations.
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Cosmology and Nongalactic Astrophysics
Big-Bang Nucleosynthesis and WIMP Dark Matter Freeze-Out as Probes of Yukawa Cosmology
Ava Shahbazi Sooraki and Ahmad Sheykhi
We investigate Big-Bang Nucleosynthesis (BBN) in the context of Yukawa cosmology. We first derive the modified Friedmann equations by starting from the first law of thermodynamics on the apparent horizon. Using observational data on \(^4\mathrm{He}\), deuterium, and \(^7\mathrm{Li}\) abundances, we place stringent bounds on the Yukawa coupling \(\alpha\). The \(^4\mathrm{He}\) and deuterium constraints are mutually consistent (\(-0.24 \lesssim \alpha \lesssim 0.12\)), while \(^7\mathrm{Li}\) requires $\alpha \in [-0.76,\,-0.72]$. This indicate that Yukawa cosmology cannot resolve the Lithium Problem. We then extend our analysis to WIMP freeze-out, and show that the modified Hubble parameter alters the relic abundance, yielding an independent constraint \(-0.017 \lesssim \alpha \lesssim 0.018\) from \(\Omega_{\mathrm{CDM}}h^2 = 0.120 \pm 0.001\). We also derive the modified time-temperature relation, and show that the positive \(\alpha\) raises the early Universe temperature. Our analysis demonstrates that BBN and dark matter relic abundance serve as complementary probes of modified
gravity. Our studies confirm that Yukawa cosmology is a testable framework for early-Universe physics.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Observational constraints on fractional holographic dark energy in the light of DESI DR2
Qihong Huang, Yuchen Zhang, Bing Xu et al. (+1 more)
Based on the fractional
entropy from fractional
quantum mechanics, fractional holographic dark energy (FHDE) has been proposed with the Hubble horizon as the IR cutoff (FHDEH). We extend this framework by adopting the future event horizon and the particle horizon as the IR cutoff, proposing the FHDEF and FHDEP models. Using the SN+OHD+DESI DR2
dataset to constrain these models, we find that all three models provide a marginally lower $\chi^{2}_{min}$ compared to $\Lambda$CDM but without significant preference according to AIC and BIC. When CMB distance priors are included, the FHDEH and FHDEP models are strongly ruled out. We further analyze the cosmological
evolution for these models, and find that only the FHDEF model predicts nearly identical evolutions of $\Omega_{m}$ and $\Omega_{de}$ to those of the $\Lambda$CDM model across
cosmic history, but its deceleration parameter $q$ deviate from the $\Lambda$CDM model in the future, indicating richer late time dynamics beyond the standard $\Lambda$CDM cosmology.
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All authors Qihong Huang, Yuchen Zhang, Bing Xu, Kaituo Zhang
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Correlated parity violation in gravity and electromagnetism from five-dimensional spacetime
Haomin Rao, Yunlong Zheng, Qi-Zhe Hou et al. (+2 more)
Parity violation in the gravitational and electromagnetic sectors has been extensively investigated, yet the two are conventionally treated as independent phenomena. This separation, however, may be a four-dimensional prejudice. In higher-dimensional spacetime,
gravity and electromagnetism may share a common
geometric origin—and so, perhaps, does their parity violation. In this paper, we pursue this idea by constructing parity-violating Kaluza-Klein models in both Riemannian and teleparallel geometries. In Riemannian geometry, the simplest five-dimensional parity-violating term reduces to several complicated four-dimensional terms, including the familiar gravitational Chern-Simons term, which suffers from a ghost instability. In teleparallel geometry, however, the result is strikingly simple. The simplest five-dimensional parity-violating term reduces to only two ghost-free terms—the familiar Nieh-Yan term and the standard electromagnetic Chern-Simons term. Remarkably, the model predicts that the helicity-dependent dispersion shift for electromagnetic waves is exactly six times that for gravitational waves, $\Delta\omega^{2}_{ EM}=6\,\Delta\omega^{2}_{GW}$, a background-independent relation. This relation offers a falsifiable test of unification through joint
cosmic microwave background and gravitational wave birefringence observations.
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All authors Haomin Rao, Yunlong Zheng, Qi-Zhe Hou, Jian-Wen Ou, Changyong Zhu
Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.IM
Foreground Subtraction with a Tensor-Based Oriented Singular Value Decomposition Method for HI Experiments
Shifan Zuo, Xuelei Chen and Yi Mao
We introduce a native tensor-based framework for foreground mitigation in 21\,cm intensity mapping (IM), utilizing the Oriented Singular Value Decomposition (O-SVD)
algorithm. While 21\,cm IM is a powerful probe of the large-scale structure of the Universe, its efficacy is severely limited by astrophysical foregrounds that are orders of magnitude brighter than the cosmological signal. Traditional mitigation strategies often necessitate flattening multidimensional data cubes into two-dimensional
matrices, a process that potentially compromises the intrinsic spatial-spectral correlations by treating distinct spatial pixels as independent samples. By treating multi-frequency sky maps and angular power spectra as third-order tensors, the O-SVD method performs decomposition directly on the multilinear
manifold, preserving the underlying physical
topology and leveraging the distinct coherence properties of astrophysical foregrounds across different dimensions. We demonstrate the performance and versatility of the O-SVD framework through its application to high-fidelity simulations from the SKA Science Data Challenge 3a (SDC3a) and real-world observational data from the Tianlai Cylinder Pathfinder Array. Our results indicate that O-SVD provides a robust and universal approach for foreground subtraction, achieving high-fidelity signal recovery while offering superior performance compared to conventional
matrix-based Singular Value Decomposition (SVD) methods.
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Cosmology and Nongalactic Astrophysics
Multi-tracer mass bias in matched cosmic voids from SDSS DR7 and the ELUCID constrained simulation
Youcai Zhang, Xiaohu Yang, Hong Guo et al. (+1 more)
Cosmic voids provide a unique environment for studying the relationship between
galaxies, subhaloes, and dark matter in the underdense Universe. Using the SDSS
galaxy catalogue and the ELUCID constrained simulation, we establish an observationally anchored framework for measuring multi-tracer mass bias within matched
cosmic voids. A sample of 102 matched void pairs is constructed to directly compare
galaxy, subhalo, and dark matter mass distributions within an observationally constrained realisation of the local Universe. We find that both the
galaxy-to-dark matter and subhalo-to-dark matter mass ratios decrease toward void centres, indicating that luminous and
halo tracers become increasingly depleted relative to the underlying matter distribution in the deepest underdensities. In contrast, the
galaxy-to-subhalo mass ratio exhibits substantially larger statistical uncertainties within the inner void regions ($r/R_{\rm v}\lesssim0.5$). By comparing measurements obtained using independent and common coordinate frameworks, we show that coordinate offsets contribute to the observed scatter but cannot fully account for the large uncertainties. The remaining uncertainty primarily arises from the severe scarcity of massive subhaloes ($\log_{10}(M_{\rm sub}/h^{-1}M_\odot)\ge11.8$) within void interiors, which greatly reduces the number of statistically valid measurements near void centres. Our results provide an empirical characterization of multi-tracer mass bias in observationally constrained
cosmic environments and demonstrate the importance of accounting for coordinate consistency and tracer scarcity when interpreting such measurements in extreme underdense regions.
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All authors Youcai Zhang, Xiaohu Yang, Hong Guo, Peng Wang
Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.HE
Locating the missing baryons in the warm-hot intergalactic medium with fast radio bursts and the Sunyaev-Zel'dovich effect
Dao-Hong Zhai, F.Y. Wang, Zi-Gao Dai et al. (+1 more)
Traditional astronomical censuses in the late-time Universe can only account for a fraction of the baryonic matter budget. Hydrodynamical simulations predict that the missing baryons reside in the vast filamentary structures of the
cosmic web as a highly diffuse, warm-hot intergalactic medium (WHIM). Observing the WHIM directly has remained a long-standing challenge due to its typical temperature. In this study, we report the first detection of spatial cross-correlations between the dispersion measures (DMs) of fast
radio bursts (FRBs) from the second CHIME/FRB catalog and the thermal Sunyaev-Zel'dovich (tSZ) Compton-$y$ map from the Planck satellite. By masking virialized
galaxy clusters to isolate the diffuse signal, we find a positive correlation with a probability $>99.77\%$ between FRBs and tSZ maps. Our joint parameter inference constrains the fraction of
cosmic baryons in the WHIM to be $f_{\rm WHIM}=0.48$ with a $68\%$ confidence interval of $0.27<f_{\rm WHIM}<0.61$, anchored at a mean WHIM temperature of $2.4 \times 10^6\ {\rm K}$. More rigorous masking strategies confirm the signal originates from the WHIM instead of
galaxy clusters. Our result demonstrates that the missing baryons are residing in the diffuse gas within the
cosmic web, closing the
cosmic baryon budget in the local Universe.
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All authors Dao-Hong Zhai, F.Y. Wang, Zi-Gao Dai, Renyue Cen