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Physics Astrophysics Cosmology and Nongalactic Astrophysics

astro-ph.CO Watch Cosmology and Nongalactic Astrophysics

Sunday 13 September

Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.HE

NICER neutron stars with dark energy and dark matter: effects on the inferred equation of state

Nathan Rutherford, Chanda Prescod-Weinstein and Anna Watts

[Abridged] In this work, we compare neutron stars where dark energy or dark matter are present in the core, contrasting them against purely baryonic stars with the same central energy density. From this comparison, we find that the dark energy models are more constrained by neutron star observations than the dark matter models, suggesting that neutron stars can place strong constraints on dark energy parameters. We consider four configurations: purely baryonic neutron stars described by a piecewise polytropic (PP) equation of state (EoS), baryonic stars admixed with bosonic or fermionic asymmetric dark matter (ADM) cores, and stars with a dark energy core and baryonic shell, where the dark energy is described by the modified Chaplygin dark fluid (MCDF). Using the masses and radii of PSR J0740$+$6620, PSR J0437$-$4715, and PSR J0030$+$0451, we employ Bayesian inference to investigate how accounting for bosonic/fermionic ADM and MCDF cores affects the inferred neutron star properties. We find that MCDF cores, more than PP and ADM admixed models, substantially broaden neutron star mass-radius and pressure-energy density posterior distributions. Moreover, the MCDF EoS parameters can be tightly constrained. While bosonic and fermionic ADM cores decrease the inferred maximum mass, their posteriors strongly coincide with those of the PP model for ADM mass-fractions $F_\chi \leq 5\%$. These results demonstrate that current mass-radius observations cannot rule out MCDF cores, but they can constrain the MCDF parameter space to narrow regions. ADM admixed neutron stars, however, remain observationally identical to purely baryonic stars for all explored mass-fractions, even with improved mass-radius uncertainties. This suggests that mass-radius measurements alone are insufficient to detect ADM core inside neutron stars and that independent astrophysical or particle physics probes will be required.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

The Connection between Halo Assembly History and the Stellar Distribution I: The Central Stellar Mass - Richness Plane

Shuo Xu, Song Huang, Alexie Leauthaud et al. (+4 more)

Recent observations suggest intrinsic links between the stellar components of massive halos and their assembly histories. Using massive halos with $\log[M_{\rm halo}/M_\odot] \geq 13.0$ from the IllustrisTNG-300 simulation, we explore differences in secondary halo properties between samples selected by central galaxy stellar mass and satellite richness. For group-like masses, we find that halos selected by the outskirts stellar mass of their central galaxies between 50 and 100 kpc ($M_{\star,[50,100]}$) have similar halo mass distributions to those selected by intrinsic satellite richness ($\lambda_{10, R_{200}}$), but differ significantly in assembly history: $M_{\star,[50,100]}$-selected halos are more concentrated and formed earlier. At higher masses ($\sim10^{14}~M_\odot$), intrinsic richness becomes the better halo-mass proxy, but only when projection effects are ignored. We find that the difference-set test selects comparable halo-mass samples most effectively when the two proxies have similar scatter. Projection effects and baryonic physics do not alter the main trends but remain important caveats for observational applications. Our findings show that the central stellar mass-richness plane is a powerful tool for selecting halos with particular accretion histories, offering new insights into the galaxy-halo connection in the era of deep imaging and precision lensing surveys such as Euclid and LSST.
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All authors Shuo Xu, Song Huang, Alexie Leauthaud, Benedikt Diemer, Katya Leidig, Conghao Zhou, Carlo Cannarozzo

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

From CMB to LHC: A hybrid inflation model with gauged scale symmetry

Jinger Wu, Mei Huang, Qi-Shu Yan et al. (+1 more)

We propose a hybrid inflation model based on gauged scale symmetry, in which an axion-like field drives inflation while the Standard Model Higgs serves as the waterfall field. During slow-roll inflation, the Higgs is trapped in the electroweak-symmetric vacuum. When the inflaton reaches a critical value, the Higgs acquires a nonzero vacuum expectation value and and triggers electroweak symmetry breaking (EWSB) through the waterfall dynamics. We identify viable parameter regions that simultaneously accommodate current cosmic microwave background observations and Higgs data from the Large Hadron Collider. The relaxation mechanism connects the inflationary and electroweak scales by reducing the large vacuum-energy contribution required during inflation. Our framework thus provides a dynamical connection between inflation and EWSB.
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All authors Jinger Wu, Mei Huang, Qi-Shu Yan, He-Xu Zhang

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Simulation of PBH formation in a matter-dominated universe

Chul-Moon Yoo, Albert Escrivà, Tomohiro Harada et al. (+1 more)

We investigate primordial black hole (PBH) formation during an early matter-dominated era using fully nonlinear numerical relativity. The initial condition is set by a functional form of the curvature perturbation including ellipticity, which makes the configuration triaxial. Two kinds of matter descriptions are considered: dust fluid and collisionless particles. In the dust fluid description, numerical computation crashes associated with the appearance of a singularity at which the fluid density diverges, unless the singularity is hidden well inside the apparent horizon. We found that, for the dust fluid description, to observe the horizon formation before calculations crash, the initial amplitude must be larger than the previous analytic estimation by a factor of 2. On the other hand, with the particle system description, calculations do not crash, and we may observe black hole formation after subsequent evolution of the system. Then the threshold of black hole formation is significantly smaller than the previous analytic estimation by an order of magnitude.
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All authors Chul-Moon Yoo, Albert Escrivà, Tomohiro Harada, Kazunori Kohri

Saturday 12 September

Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.IM

A compact time-domain reduced order quadrature for gravitational wave inspirals with non-stationary noise

Benjamin Zhang, Kris Pardo and Bence Bécsy

We develop the first time-domain reduced order quadrature for gravitational waves in the early inspiral period, motivated by the need for dataset compression in the presence of gaps, uneven sampling, and dense covariance matrices. A single reduced basis with 1290 elements can represent inspirals from supermassive black hole binary sources with chirp masses between $10^7-10^{10}$ $M_\odot$, but in the presence of non-stationary noise $\sim 1290^2$ reduced order quadrature weights must be stored. We are able to reduce the stored weights by a factor of two by partitioning our parameter space by GW frequency, with relative waveform/likelihood accuracies remaining below $10^{-5}$/$10^{-3}$ after partition. Finally, we point out that heterodyning can be combined with reduced order methods with no loss in accuracy. Our reduced order quadrature makes inspiral searches in the time domain feasible for both pulsar timing arrays and relative stellar astrometry.
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Cosmology and Nongalactic Astrophysics

A comprehensive assessment of weak-lensing inferred circular velocity profiles of isolated galaxies

Sri Devaki Meduri and Shantanu Desai

We fit the circular velocity data, derived from weak lensing observations of isolated galaxies selected from the KiDS survey in four baryonic mass bins, using three different dark matter profiles. These include NFW, Burkert, and pseudo-isothermal profile. We find that the NFW and Burkert profiles cannot adequately fit the circular velocity data for all the four baryonic mass bins, whereas only the pseudo-isothermal profile can fit the data for all the four bins.
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Cosmology and Nongalactic Astrophysics

Measuring the spatio-temporal variation of fundamental physical constants using the OH sum rules

Renzhi Su and Minfeng Gu

In this paper, we introduce a method to constrain the variation of fundamental physical constants predicted by grand unified theories. This approach utilizes OH sum rules, which exhibit different forms depending on the physical conditions of the OH gas. Employing a least-squares technique, we can directly derive the relative velocity offsets among four OH lines in each ground state. This circumvents the need for spectral profile fitting, which is often unfeasible for spectra with complex profiles. Moreover, this method remains robust even when portions of the spectra are contaminated by radio frequency interference (RFI). Applying this method to a Galactic source G035.1+0.5, we obtained a stringent constraint of $\Delta X/X=(-1.8\pm5.1)\times10^{-6} $, where $X=\mu^{-1}\alpha^{2}g_{p}^{0.54}$. This method is expected to play a crucial role in extracting fundamental physics from large datasets of upcoming Square Kilometre Array (SKA) telescope.
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Cosmology and Nongalactic Astrophysics

Consistent treatment of flavour-specific neutrino self-interactions in cosmology

Gabriela Barenboim, Marco Drewes and Isabel M. Oldengott

We study the impact of flavour-specific neutrino self-interactions on the CMB anisotropy spectrum and consistently take into account neutrino mixing. Starting from the neutrino quantum kinetic equations, we derive the neutrino Boltzmann hierarchies for the neutrino mass states. Our work shows that most scenarios of flavour-specific neutrino self-interactions are well approximated by a combined fluid approach. In practice, this implies that existing CMB bounds on the effective neutrino coupling are weakened by a factor $\sqrt{2}$ for scenarios in which only two neutrino flavours interact (irrespective of which flavours). If only one neutrino flavour interacts the bounds are weaker by a factor $\sqrt{6}$, with the only caveat that the combined fluid approach is less reliable for only $\nu_e$ interacting.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

A Unified Numerical Study of Axion Stars: From the Nonrelativistic Regime to General Relativity

Parisa Arabameri, Paola Arias, Francisco Colipí-Marchant et al. (+1 more)

Axion-star mass-radius relations are commonly computed using different orders of relativistic approximation, making it important to determine where these descriptions remain reliable. We perform a unified numerical comparison of axion-star ground-state configurations in the Newtonian Schrödinger-Poisson description, first- and second-order relativistic effective field theories, and the full Einstein-Klein-Gordon system for a real scalar field. Using the same attractive quartic self-interaction in all four descriptions, we scan $|\widetilde{\lambda}|=(M_{\rm Pl}/f_a)^2$ and determine the maximum masses and corresponding enclosed-mass radii. All descriptions recover the common large-$|\widetilde{\lambda}|$ dilute-star scaling, while substantial differences appear at weak and moderate coupling. The relativistic EFTs interpolate systematically between the Newtonian and full-GR results. For part of the maximum-mass sequence where $\max|\phi|/f_a=O(1)$, we test the temporal-harmonic and potential truncations explicitly in full GR. The higher-harmonic expansion shows rapid convergence, while restoring the complete single-cosine potential changes the maximum mass only at the percent level and $R_{95}$ at the several-percent level. Together with the systematic convergence of the relativistic EFT descriptions toward full GR, these results show that the large weak-coupling departure from the Schrödinger-Poisson prediction reflects the breakdown of the nonrelativistic structural description. Our results provide a systematic benchmark for determining when Newtonian, relativistically corrected, or fully general-relativistic descriptions are required for axion-star structure. The numerical implementation used in this work is available in the Axion Star Solvers repository at https://github.com/Parisa-Arabameri/AxionStar.
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All authors Parisa Arabameri, Paola Arias, Francisco Colipí-Marchant, Enrico D. Schiappacasse

Friday 11 September

Cosmology and Nongalactic Astrophysics

CHEX-MATE: X-ray surface brightness discontinuities across a representative cluster sample

Maria Giulia Campitiello, Stefano Ettori, Lorenzo Lovisari et al. (+20 more)

We analyze the presence of X-ray surface brightness (SB) discontinuities, such as shocks and cold fronts, in the intracluster medium (ICM) of the 116 galaxy clusters from the CHEX-MATE sample. These features arise from accretion-related processes, including the merging of subclumps onto the main cluster halo and the sloshing of cold gas in a higher-entropy environment. We identify these structures in the XMM CHEX-MATE maps by examining both the SB residuals, obtained by subtracting a cluster model from the observations, and the gradient variations across X-ray images. We validate our method with an extensive analysis and comparison of the discontinuities described already in the literature. Our analysis reveals 66 discontinuities, 32 of which are newly detected, in 48 objects ($\sim$41%). We find that discontinuities in relaxed systems tend to be closer to the core, weaker, and less aligned with the global X-ray morphology compared to those in disturbed systems. Using wavelet-based temperature maps, we provide a preliminary classification of these discontinuities, proposing the occurrence of 8 putative shocks and 34 cold fronts. Furthermore, about 48% of the systems with extended radio emission show evidence of ICM discontinuities; conversely, $\sim$88% of the objects with detected discontinuities have an associated diffuse radio emission. This work also explores the limitations of using XMM data, characterized by relatively low spatial resolution, for detecting and analyzing such features, highlighting the challenges and potential biases introduced by instrumental constraints.
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All authors Maria Giulia Campitiello, Stefano Ettori, Lorenzo Lovisari, Fabio Gastaldello, Hervé Bourdin, Pasquale Mazzotta, Mariachiara Rossetti, Marco Balboni, Andrea Botteon, Rossella Cassano, Federico De Luca, Dominique Eckert, William Forman, Massimo Gaspari, Simona Ghizzardi, Myriam Gitti, Scott T. Kay, Ben J. Maughan, Etienne Pointecouteau, Gabriel W. Pratt, Elena Rasia, Jack Sayers, Mauro Sereno

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Direct detection of right-handed fermionic dark matter: electron-recoil measurements in Xe atoms

Santiago Collazo, Carlos Argüelles, Soroush Shakeri et al. (+1 more)

We present theoretical estimations of the event rates for the interaction between a right-handed fermionic dark matter with an electron bound to a xenon atom. Motivated by recent astrophysical and cosmological constraints on a fermionic dark matter candidate in the sub-MeV mass range, we study such an interaction through an effective electromagnetic channel where the output consists of standard-model particles. This mechanism allows right-handed neutral dark matter fermions to couple with standard-model particles with the interchange of $W^{\pm}$ or $Z$ bosons, without the need to add extra fields. We generalize and extend previous results on this type of channels, by including for the ionization form factor arising from the interaction of the fermionic candidate with bound electrons. In addition, we compute the sensitivity curves for different direct detection experiments in such a challenging light particle mass range.
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All authors Santiago Collazo, Carlos Argüelles, Soroush Shakeri, Osvaldo Civitarese

Cosmology and Nongalactic Astrophysics

Supernova Cousins: The Intrinsic Dispersion and Environmental Dependence of Type Ia Supernovae in Galaxy Groups with TITAN

Allison Blum, Erik R. Peterson, David O. Jones et al. (+7 more)

At low redshift, scatter in the Type Ia supernova (SN Ia) Hubble diagram is increased by peculiar velocities (PVs) and correlations between SN distances and their host-galaxy environments, limiting the precision of cosmological distance measurements. We investigate these effects using 1086 spectroscopically-confirmed SNe Ia from the Type Ia Supernova Trove from ATLAS in the Nearby Universe (TITAN) sample in the redshift range $0.01<z<0.05$. We identify 314 group-associated SNe, including 80 SN "cousins" occurring in different galaxies within 32 common groups. We first examine whether using the group-averaged redshifts of SNe in galaxy groups can mitigate PV-induced scatter; however, we find that the Hubble residual scatter increases slightly from $0.184^{+0.017}_{-0.009}$ mag using individual host-galaxy redshifts to $0.200^{+0.016}_{-0.015}$ mag using group-averaged redshifts. For the sample of SN cousins, we next analyze pairwise differences in their distances and compare their scatter to the Hubble residual scatter of the full SN sample. For analysis variants that limit line-of-sight differences in distance modulus between cousins, we find $\sim$30-40% lower scatter from SN cousins at significances of 2.3-2.8$\sigma$. We also find tentative evidence that these differences in scatter may be driven by the youngest groups, with a 2$\sigma$ reduction in scatter for groups with high fractions of spiral galaxies. These results suggest that SN cousins may provide a novel route for increasing SN Ia distance precision and understanding the role of host-galaxy and group properties on SN Ia distance measurements.
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All authors Allison Blum, Erik R. Peterson, David O. Jones, R. Brent Tully, Elijah G. Marlin, Yukei S. Murakami, Jack W. Tweddle, Dillon Brout, Mitchell Dixon, Stephen J. Smartt

Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

The GMRT CAT$z$1-COSMOS Survey: HI 21 cm emission from star-forming galaxies at $z\approx1$ in the COSMOS field

Balpreet Kaur, Nissim Kanekar, Aditya Chowdhury et al. (+1 more)

We report a 216-hr upgraded Giant Metrewave Radio Telescope (GMRT) Band-4 $550-850$ MHz observation of the COSMOS field, using 7 GMRT pointings to cover an area of $2.4$ sq. deg., with on-source times of $67$ hrs in the central pointing, and $89$ hrs distributed across the other six pointings. We stacked, at a spatial resolution of 90 kpc, the HI 21 cm emission signals from 8,122 star-forming galaxies with accurate spectroscopic redshifts and lying within the FWHM of the GMRT primary beam at their redshifted HI 21 cm frequencies. We detect the stacked HI 21 cm signal from the 8,122 galaxies at $4.2\sigma$ significance, obtaining an average HI mass of $\langle{M_{\scriptsize{\textrm{HI}}}}\rangle=(15.5\pm3.7)\times10^9 \textrm{M}_\odot$. This is only the second galaxy population at $z\approx1$ with a measurement of the average HI content; the other being the blue star-forming galaxies in the DEEP2 fields. We also detected the median 1.4 GHz radio continuum emission signal from the 8,122 galaxies by stacking the GMRT 680 MHz continuum images, obtaining a weighted-median star-formation rate (SFR) of ${8.90\pm0.92}~M_\odot$ yr$^{-1}$. We measure a characteristic HI-to-stellar mass ratio of $\langle{M_{\scriptsize{{\textrm{HI}}}}}\rangle/\langle{M_\star}\rangle=(1.15\pm0.27)$ and a characteristic HI depletion timescale of $\langle{M_{\scriptsize{{\textrm{HI}}}}}\rangle/\textrm{SFR}=(1.74\pm0.45)$ Gyr for star-forming galaxies at $\langle{z}\rangle=1.081$ in COSMOS, both consistent with earlier measurements for the blue, star-forming DEEP2 galaxies at $z\approx1$. Our results support the evidence from the DEEP2 survey that the observed decline in the SFR density at $z<1$ is due to insufficient accretion of atomic gas from the intergalactic medium to replenish the gas reservoir consumed in the process of star-formation.
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All authors Balpreet Kaur, Nissim Kanekar, Aditya Chowdhury, Jayaram N. Chengalur

Cosmology and Nongalactic Astrophysics

Diffraction of gravitational waves by extended dark objects

Nikita Blinov and J. Leo Kim

Many dark sector models predict the formation of dark objects, such as solitons and dark stars, which can be searched for through their gravitational lensing of gravitational waves (GWs). Although these objects vary widely in size and compactness, most GW lensing studies have focused on point-like lenses. The finite size of an extended lens is important when it exceeds its Einstein radius. We evaluate the frequency-dependent effects on GW waveforms from extended lenses and demonstrate that they can be probed with current and future GW data. While finite-size effects can weaken the bounds on the fraction of dark matter in these objects compared to the point-like limit, current GW data provides complementary constraints to other gravitational tests for lens masses between $10^2M_\odot$ and $10^5M_\odot$; future LIGO-Virgo-KAGRA data and next-generation observatories will surpass their sensitivity. As expected, we find that the finite-size effects are important when the lens radius exceeds $\sim \text{few} \times 10^{6}R_\odot (M_L/100 M_\odot)^{1/2}$. Interpreting these constraints within specific models (a simple dissipative dark sector and axion stars), we show that current and future observations probe significant portions of the microphysical parameter space.
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Cosmology and Nongalactic Astrophysics

Complete Second-Order Relativistic Derivation of the Observed Pulsar Timing Modulations

Matteo Magi and Jaiyul Yoo

We present a fully nonlinear relativistic description of the observed pulsar timing modulations, defined through the ratio of the proper-time intervals between two successive emissions of radio pulses and their observations by a pulsar timing array. Working in the limit of a vanishing emission interval, we derive the observed pulsar timing modulation to second order in relativistic perturbation theory around a Minkowski background, without fixing a gauge and retaining the full scalar, vector, and tensor content of the metric perturbations. Although the derivation naturally introduces several gauge-dependent intermediate quantities, we explicitly demonstrate that they combine into a coordinate-independent expression. Moreover, we explicitly show that the second-order timing modulation from two neighboring radio pulses coincides with the observed redshift, defined as the fractional change in wavelength along a single geodesic. The agreement represents a nontrivial second-order realization of the exact nonlinear equivalence proven in Magi & Yoo 2026.
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Cosmology and Nongalactic Astrophysics

The Loud Tail of the Supermassive Black Hole Binary Population: Multimessenger Candidates and Prospects for SKAO

Juhan Raidal, Ville Vaskonen, Juan Urrutia et al. (+1 more)

We assess whether electromagnetically identified supermassive black hole (SMBH) binary candidates populate the rare, high-amplitude tail of the gravitational wave (GW) amplitude distribution. Using an SMBH binary population model fitted to the NANOGrav 15-year data, we find that 3C~66B and Mrk~501 are likely to stand out from the GW background, making them promising targets for individual-source searches. Furthermore, we show that individual detections can probe the binary hardening mechanism, as models with strong environmental hardening predict a higher abundance of individually resolvable binaries than purely GW-driven models. Applying the same population fits and accounting for the confusion noise from the unresolved population, we forecast that the Square Kilometre Array Observatory (SKAO) will resolve tens of individual binaries, with 3C~66B robustly detectable.
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All authors Juhan Raidal, Ville Vaskonen, Juan Urrutia, Hardi Veermäe

Cosmology and Nongalactic Astrophysics

Big Bang For Your Helium Buck

Marilena Loverde, Murali M. Saravanan and Zachary J. Weiner

We study the implications of a recent measurement of the primordial helium fraction from the Large Binocular Telescope for cosmological inference from the cosmic microwave background. We show that LBT establishes the robustness of cosmological parameters to theoretical assumptions about big bang nucleosynthesis: its empirical calibration of the helium fraction enables constraints on cosmology and inflation that are agnostic to BBN but as precise as those that instead enforce standard BBN predictions. Future CMB surveys require at most a marginal improvement in precision over LBT to maximize their BBN-agnostic constraining power when the radiation density is free (and no more than a factor of two improvement across all cases we consider). We then apply the LBT measurement to a number of scenarios that feature new physics in BBN and the CMB. First, we constrain nonstandard radiation sectors (interacting and free-streaming) and search for evolution of the radiation abundance between nucleosynthesis and recombination. We then test models that alleviate the Hubble tension and the tension between CMB and baryon acoustic oscillation data, including self-interacting light relics and varying fundamental constants; LBT precludes most but not all of the models we consider via their effect on BBN. Finally, we use the LBT measurement as an indirect but independent test of the neutron lifetime anomaly, inferring values that are consistent with "bottle" experiments and $2.4 \sigma$ below "beam" experiments.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

High-redshift supermassive black hole population from core-collapse in self-interacting dark matter halos

Sambo Sarkar and Ujjal Kumar Dey

Self-interactions between dark matter (DM) particles facilitate the inter-particle redistribution of energy within the central region of DM halos. Recent studies of dark matter spikes around massive black holes, and the diversity in rotation curves of dark matter rich low-mass galaxies motivate the exploration of self-interaction cross-section $\mathcal{O}(10)\,\rm cm^2/gm$. At such high scattering rates, DM can lead to the formation of supermassive black hole seeds, through the gravothermal collapse of halo cores, under certain cosmological conditions. Quasars near cosmic dawn are powerful probes for examining the formation scenario of high redshift supermassive black holes, and their connection to structure formation. In this work we point out the favorable initial cosmological conditions that are likely to provide the black hole seeds resulting in supermassive black holes, mediated by core-collapse in self-interacting dark matter halos. Employing a semi-analytic prescription of core formation, and realistic mass accretion and halo merger histories, we compare the existing observations of high-redshift supermassive black holes with those predicted for our core-collapse framework. We find the median values of velocity-dependent self-interacting dark matter parameter space $\sigma/m_{\chi}\sim 56\, \rm cm^2/gm$, and $\omega=101\,\rm km/s$, assuming an Eddington accretion rate of unity. Sub-leading values are also presented for sub and super-Eddington accretion rates. We also report the derived self-interacting dark matter model parameters to account for the observed binned supermassive black hole mass functions at high-redshifts.
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Cosmology and Nongalactic Astrophysics

Probing Inflationary Origins of Primordial Black Holes with LIGO–Virgo–KAGRA O1–O4a data

Haipeng An, Huai-Ke Guo, Mai Qiao et al. (+3 more)

Large primordial curvature perturbations not only produce primordial black holes (PBHs) but also inevitably source a scalar-induced stochastic gravitational-wave background upon horizon reentry. We analyze the combined LIGO–Virgo–KAGRA O1–O4a data to constrain two representative inflationary mechanisms for generating such perturbations: ultra-slow-roll inflation and an inflationary phase transition. Detecting no evidence for either scenario, we place 95% credible upper limits on the curvature-spectrum amplitude across the frequency range accessible to ground-based interferometers. Translated into the PBH context, these limits already exceed conventional constraints, probing abundance fractions far below unity. Our results remain robust even when the PBHs themselves are too rare to be directly detected or have evaporated. This work demonstrates that stochastic gravitational-wave observations offer a powerful and complementary probe of small-scale inflationary physics and PBH formation, with upcoming interferometers promising to extend sensitivity to a wider range of inflationary epochs and PBH masses.
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All authors Haipeng An, Huai-Ke Guo, Mai Qiao, Lian-Tao Wang, Chen Yang, Yue Zhao

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ex

The DALI Haloscope: A Magnetized Phased Array Coupled to a Semi-Open Fabry–Pérot Resonator

Javier De Miguel, Antonios Gardikiotis, Eduardo David González-Carretero et al. (+10 more)

DALI is an axion haloscope consisting of a magnetized phased array backed by a conducting mirror and coupled in the near field to a semi-open Fabry–Pérot resonator. The applied static magnetic field makes both the dielectric interfaces and the conducting mirror sensitive to axion-induced electromagnetic conversion. Each interface acts as a radiating surface, and the resulting fields are projected onto the mode collected by the resonator and delivered to the receiver. We derive the detected power in terms of the power available from the magnetized mirror, the coherent contribution of the dielectric interfaces, the transverse mode overlap, the loaded quality factor, and the receiver-coupling coefficient. This formulation separates two distinct enhancement mechanisms. The dielectric-interface emissions may add coherently, producing a dielectric boost, while the semi-open Fabry–Pérot resonator provides enhancement through resonant storage of the coupled electromagnetic field. These contributions depend differently on the dielectric thicknesses, spacings, and resonant mode, and should therefore be evaluated independently. The same assembly can operate between the limits of a coherently boosted dielectric haloscope and a mirror-sourced, resonantly enhanced Fabry–Pérot haloscope. This combined architecture offers a flexible approach to resonant axion searches at frequencies for which conventional closed microwave cavities become increasingly limited in conversion volume.
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All authors Javier De Miguel, Antonios Gardikiotis, Eduardo David González-Carretero, Elvio Hernández-Suárez, Roger J. Hoyland, Enrique Joven, Abaz Kryemadhi, Marios Maroudas, Chiko Otani, J. Alberto Rubiño-Martín, Yannis K. Semertzidis, Michael E. Tobar, Konstantin Zioutas

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ex

Constraints on Galactic Dark Photons from a DALI Prototype

Javier De Miguel, Antonios Gardikiotis, Elvio Hernández-Suárez et al. (+10 more)

An analysis of 36 hours of data from a DALI haloscope reveals no statistically significant excess attributable to dark-photon dark matter. We therefore set new constraints in the 6.88691–6.91792 GHz band, reaching a dark-photon-to-photon kinetic mixing strength of $\chi\lesssim 6.8\times10^{-14}$ at $28.54 \, \mu\mathrm{eV}$. To our knowledge, this result established the strongest laboratory-based exclusion limit in this frequency range.
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All authors Javier De Miguel, Antonios Gardikiotis, Elvio Hernández-Suárez, Roger J. Hoyland, Enrique Joven, Abaz Kryemadhi, Haroldo Lorenzo-Hernández, Marios Maroudas, Chiko Otani, J. Alberto Rubiño-Martín, Yannis K. Semertzidis, Michael E. Tobar, Konstantin Zioutas

Thursday 10 September

Cosmology and Nongalactic Astrophysics

Probabilistic characterization of blending with LSST and application to cluster lensing cosmology

Manon Ramel, Cyrille Doux, Marine Kuna et al. (+9 more)

Next-generation galaxy surveys, like the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST), will deliver unprecedented depth and sky coverage, enabling precise measurements of cosmic probes such as weak lensing and galaxy clustering. However, increased imaging depth leads to significant blending of galaxy images, particularly in dense fields like galaxy clusters. This blending, exacerbated by atmospheric blurring in ground-based observations, contaminates galaxy property measurements and causes source confusion. To simultaneously capture these effects, we develop a probabilistic framework introducing the blending entropy, a metric quantifying the ambiguity in matching detected objects to true galaxies or external reference sources. Using simulated data from the DESC Data Challenge 2 (DC2), we characterize blending in LSST data and quantify its impact on cluster lensing cosmology around cosmoDC2 halos. We demonstrate that imposing a blending entropy threshold of $S_b<0.2$ effectively filters out highly blended objects (around 25%), which are especially prevalent near the survey's magnitude limit and are associated with higher errors in shape measurements and photometric redshifts. Applying this cut substantially reduces blending-induced biases in cluster lensing profiles and mass estimates, thereby mitigating systematic errors in cosmological parameters—most notably reducing tension in $\sigma_8$ estimates. Our method is readily generalizable to other static probes and offers a practical path forward for real data analyses, particularly when leveraging overlapping high-resolution datasets from spaced-based missions such as Euclid or the Roman Space Telescope, where these external datasets can act as reference catalogs to improve the identification of blended sources in LSST data.
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All authors Manon Ramel, Cyrille Doux, Marine Kuna, Michel Aguena, Céline Combet, Shuang Liang, Constantin Payerne, Camille Avestruz, Alex I. Malz, Marina Ricci, Nikolina Šarčević, the LSST Dark Energy Science Collaboration

Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.HE

Which Type Ia supernova observables best indicate the ages of their progenitor stars?

Young-Lo Kim, Chul Chung, Young-Wook Lee et al. (+3 more)

Type Ia supernovae (SNe Ia) observables, such as the light-curve shape and the colour, are expected to contain information about the progenitor star. In this work, we explore this information, with a particular focus on the age of the SN Ia progenitor star. For this, we construct the SN Ia progenitor age distribution (SPAD) and compare it to the observed distributions of light-curve shape (x1) and the colour (c) parameters in a volume-limited SN Ia sample. We find that SPAD and the x1 distribution share a common shape: a young/high-x1 peak and an old/low-x1 bump in the tail, and this shape varies systematically with redshift. In contrast, this behaviour is not evident in the c distribution. We then examine the correlation of the local age at the SN Ia explosion site, used as a proxy for the progenitor age, with x1 and c. The local age and x1 are well correlated (the linear correlation coefficient ~ -0.71), whereas the local age and c show no significant correlation (the coefficient ~ 0.08). Furthermore, we find that the x1 distribution systematically evolves with the local age. Lastly, we demonstrate that an empirical mapping approach based on SPAD successfully reproduces the observed x1 distribution across different redshift bins. Taken together, our results suggest that the light-curve shape distribution indicates progenitor age at the population level more robustly than the colour does. In particular, younger progenitors are more likely to have higher-x1 SNe Ia. We discuss an application for creating a more homogeneous sample of SNe Ia in terms of progenitor age across a wide redshift range without the Malmquist bias, thereby improving the accuracy of cosmological constraints derived from SNe Ia.
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All authors Young-Lo Kim, Chul Chung, Young-Wook Lee, Seunghyun Park, Junhyuk Son, Suk-Jin Yoon

Cosmology and Nongalactic Astrophysics

The Role of Big Bang Nucleosynthesis in Joint Cosmological Analyses

Mehmet Akharman, Nicholas DePorzio, Cara Giovanetti et al. (+1 more)

We perform joint Baryon Acoustic Oscillation (BAO) + Big Bang Nucleosynthesis (BBN) and BAO+BBN+Cosmic Microwave Background (CMB) analyses with Planck CMB and DESI DR2 BAO data, explicitly marginalizing over BBN nuisance parameters for the first time with these data combinations and paying particular attention to the impact of BBN on these results. We find in our fiducial analyses $h=0.6833^{+0.0048}_{-0.0053}$ ($\Lambda$CDM, BAO+BBN), $h=0.6823^{+0.0027}_{-0.0026}$ ($\Lambda$CDM, BAO+BBN+CMB), as well as $h=0.6791^{+0.0069}_{-0.0075},N_{\rm{eff}}=2.974^{+0.098}_{-0.099}$ ($\Lambda$CDM+$N_{\rm{eff}}$, BAO+BBN), and $h=0.6838^{+0.0052}_{-0.0054},N_{\rm{eff}}=3.065^{+0.078}_{-0.076}$ ($\Lambda$CDM+$N_{\rm{eff}}$, BAO+BBN+CMB). We demonstrate how investigator choices can impact results of joint analyses involving BBN. We provide recommendations for the treatment of BBN in light of recent work, and demonstrate a pipeline that accurately accounts for prediction uncertainties in BBN.
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All authors Mehmet Akharman, Nicholas DePorzio, Cara Giovanetti, Hongwan Liu

Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

BAQARO: Tracing Stochastic Black Hole Growth Histories and Quasar Lightcurves in a Cosmological Context

Elia Pizzati, Joseph F. Hennawi and Joop Schaye

How supermassive black holes (BHs) assemble their mass and power the luminous quasars we observe across cosmic time remain central open questions in galaxy evolution. We present BAQARO, a semi-empirical framework for BH growth. Built on subhalo merger trees extracted from the FLAMINGO-10k simulation, the model links BH growth histories to those of their host subhalos through prescriptions that capture both average trends and stochastic variability. BAQARO is constrained by the bolometric quasar luminosity function, the clustering of UV-luminous quasars, and the conditional Eddington ratio distribution function. With six free parameters controlling BH seeding, the coupling between gas accretion and halo growth, and the stochasticity and temporal coherence of accretion, the model reproduces the available observational constraints over $0 \lesssim z \lesssim 7$. Using emulators, we perform Bayesian inference and quantify the constraining power of each observable. Our main findings are: (i) BH accretion is well described by the assembly of cold gas reservoirs in halos, without requiring an explicit dependence on cosmic time. (ii) BHs rapidly assemble their mass at high redshift through stochastic episodes of super-Eddington accretion. (iii) These episodes are radiatively inefficient and persist for timescales of $\sim1\,\mathrm{Myr}$, imprinting observable signatures on quasar lightcurves, proximity zones, and clustering measurements. (iv) The merger growth channel is always subdominant, but becomes increasingly important at $z \lesssim 1$, particularly for massive BHs. BAQARO growth histories and quasar lightcurves provide a flexible framework for interpreting the rapidly expanding landscape of quasar observations, from high-$z$ accretion probed by JWST to low-$z$ mergers constrained by pulsar timing arrays.
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Cosmology and Nongalactic Astrophysics

Reconsidering the role of bright and dark gravitational-wave standard sirens for cosmology

Alberto Colombo, Sonia Triscari-Benimavò and Simone Mastrogiovanni

Gravitational-wave (GW) standard sirens have emerged as powerful probes of cosmic expansion. They are commonly divided into two classes: bright sirens, observed in coincidence with an electromagnetic (EM) counterpart, and dark sirens, detected without one. Bright sirens have often been considered the main avenue for precision cosmology; however, following the latest observing run of the LIGO-Virgo-KAGRA (LVK) collaboration, the estimates of merger rates of compact objects involving neutron stars (NSs) have decreased. In this Letter, we reconsider the role that bright and dark sirens will play in precision cosmology. We demonstrate that bright sirens, although detected in small numbers, will play a crucial role in achieving the precision needed to address the Hubble tension, primarily by breaking the degeneracy between the Hubble constant ($H_0$) and the matter density parameter ($\Omega_m$) inherent to dark sirens. Alternatively, we show that dark sirens alone can resolve the $H_0$ tension when supplemented with an external prior on $\Omega_m$. Furthermore, we present a self-consistent statistical framework for GW cosmology with bright and dark sirens, which have traditionally been treated as independent populations although they originate from the same underlying population of black holes (BHs) and NSs. Finally, we find that treating bright and dark sirens as independent populations will not significantly bias GW cosmology in the next LVK observing runs, but can lead to a biased reconstruction of the low-mass end of the mass spectrum.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.HE

Constraining dark matter using 20-year INTEGRAL/IBIS observations I: Primordial black holes

Jordan Koechler and Pedro De la Torre Luque

Primordial black holes (PBHs) in the asteroid-mass window remain a viable dark matter candidate. In the lower part of this mass range, Hawking evaporation produces electrons and positrons that generate diffuse hard X-ray emission through inverse Compton (IC) scattering on Galactic radiation fields. We present the first search for this signal using a combined spectral and morphological analysis of the 20-year INTEGRAL/IBIS observations. We construct a physically motivated model of the Galactic hard X-ray background, including IC emission from cosmic-ray electrons and unresolved accreting white dwarfs, and consistently incorporate the IC contribution from PBH evaporation. By exploiting both spatial and spectral information, we improve the separation between a possible PBH signal and astrophysical backgrounds compared to analyses based only on spectral data. We derive constraints on the PBH dark matter fraction over a broad mass range, including extended PBH mass functions and rotating PBHs. We assess the impact of uncertainties in cosmic-ray propagation and the Galactic dark matter density profile, finding that the propagation of low-energy electrons and positrons represents the main source of uncertainty in the predicted signal. Despite these limitations, our results provide competitive constraints over a wide range of PBH masses, highlighting the potential of hard X-ray observations as a complementary probe of evaporating PBHs.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

Clustering-based halo mass assignment for high-redshift galaxies: method, validation, and application to JWST

Seunghwan Lim, Sandro Tacchella, Sara Saleh et al. (+7 more)

We present a clustering-based method for inferring halo masses of high-redshift galaxies, validated using the COLIBRE simulations combined with the HOMA empirical model, which assumes star formation to be proportional to halo accretion rate and is calibrated to JWST observations. Our approach matches the two-point correlation function of galaxies in stellar mass bins to reference halo clustering, establishing the stellar-to-halo mass relation over an optimal radial range 0.5 < r_p/cMpc < 1.0. Validation against true halo masses shows minimal bias, with scatter below 0.3 dex for volumes down to (50 cMpc)^3 and redshifts to z=12, even for photometric data. Cross-validation using the native COLIBRE population shows that the method is robust to the different galaxy-halo prescriptions. Survey volume dominates the error budget: field-to-field variations in the clustering amplitude vary by factors of 3 (2) for photometric (spectroscopic) samples, translating to 0.3-0.5 dex uncertainty in halo masses. Splitting the sample by properties such as SFR, colour, and age mitigates assembly bias, offering a key advantage over abundance matching. Application to JWST (JADES) samples at z=6 and 10 yields halo masses of log M_h/M_sun = 10.52_{-0.21}^{+0.12} and 9.91_{-0.34}^{+0.19} for M_UV < -17 galaxies, with linear biases of b_h = 4.2_{-0.41}^{+0.26} and 7.7_{-1.16}^{+0.77}, respectively. Current data cannot distinguish between star formation models. Our Roman Deep Tier forecasts indicate that at z=10, the inferred halo masses for M_UV < -21 galaxies differ by 0.5 dex between bursty and non-bursty models, but the expected number of pairs limits the constraining power. Our framework provides robust, empirically-calibrated halo masses essential for interpreting JWST observations and constraining galaxy formation during reionization.
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All authors Seunghwan Lim, Sandro Tacchella, Sara Saleh, Roberto Maiolino, Lily Whitler, Joop Schaye, Evgenii Chaikin, Carlos S. Frenk, Filip Huško, Alexander J. Richings

Cosmology and Nongalactic Astrophysics

Impact of galaxy intrinsic alignments on non-Gaussian weak lensing statistics for modified gravity

Mehar Chawla, Christopher T. Davies, Joachim Harnois-Déraps et al. (+3 more)

Non-Gaussian weak lensing statistics improve the constraining power of cosmic shear data by harvesting information unavailable to two-point statistics, within and beyond the GR+$\Lambda$CDM scenario. Dark energy, total neutrino mass and deviations from GR have all been shown to be better measured with non-Gaussian lensing probes, in simplified conditions. Previous studies typically overlook the impact of secondary lensing signals, which can be large and therefore can significantly affect the conclusions. Here we investigate the impact on measurements of cosmological and modified gravity parameters in the presence of galaxy intrinsic alignments. We focus on the power spectra, lensing PDF, peaks and minima counts, void abundance and void profiles. These non-Gaussian statistics are measured from the MGLenS mock weak lensing maps, in which three cosmological parameters and one gravitational parameter are varied, either in the $f(R)$ or nDGP scenario, assuming Stage-IV lensing survey precision. These simulations are infused with the non-linear linear alignment model, allowing us to build emulators for each statistic with or without IA, and to study biases in full MCMC analyses. We show that in the absence of IA, lensing void profiles and abundance generally yield the highest Figure of Merit in the $S_8 - f_{R0}$ and $S_8 - H_0 r_{\rm c}$ planes, at times improving by an order of magnitude over two-point functions. When IA is unaccounted for, major parameter biases are observed in the cosmology sector, while the modified gravity sector is relatively unaffected. We find that these biases can generally be flagged from poor goodness-of-fit measurements, except for a few cases where IA can fully masquerade as a lower $\Omega_{\rm m}$ and lower $S_8$ cosmology.
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All authors Mehar Chawla, Christopher T. Davies, Joachim Harnois-Déraps, Baojiu Li, Joseph J. Mohr, Bipradeep Saha

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Theoretical Aspects of Direct Waves in Kerr Black Holes: Pole-Splitting Method for Ringdown Analysis

Nao Nakamoto, Naritaka Oshita and Hiroki Takeda

We formulate the theoretical aspects of direct waves (DWs) in the case of extreme-mass merger. A DW is a source-driven waveform characterized by a complex frequency $\omega_{\rm G}$, which reflects the orbital motion of the particle in the vicinity of the black hole, including a part of the orbit inside the ergoregion: its real part is governed by frame dragging and its imaginary part by the redshift of the source. Using the Green's function technique, we derive the source-driven frequency $\omega_{\rm G}$, describe its screening by the potential barrier, and discuss its relation to dynamically excited quasinormal modes (QNMs). We then introduce a pole-splitting method that divides the full waveform into a QNM-pole sector and a non-QNM sector. Unlike QNM filtering, which multiplies the waveform spectrum by a filter function and thereby deforms it through a frequency-dependent time shift (i.e., group delay), our pole-splitting method merely divides the transfer function into pole and non-pole parts, separating the full waveform. Simulating a quasi-circular plunge into a Kerr black hole with medium and rapid spins, we find that the frequency and decay rate of the non-pole sector in the dominant mode, $\ell = m = 2$, evolve consistently with $\omega_{\rm G}$-or with its screened counterpart $\omega_{\rm screen}$-establishing the DW as a probe of the ergoregion and of the redshift effect around a black hole.
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