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Physics Astrophysics Cosmology and Nongalactic Astrophysics

astro-ph.CO Watch Cosmology and Nongalactic Astrophysics

Wednesday 23 September

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

Sterile Neutrino Dark Matter Cries for GeV Heavy Neutral Leptons

Marco Drewes, Yannis Georis, Juraj Klarić et al. (+2 more)

The ordinary and dark matter in the Universe may share a common origin in the framework of a minimal extension of the Standard Model by three right-handed neutrinos. A pair of such heavy neutral leptons (HNLs) can give masses to neutrinos, generate the baryon asymmetry at the electroweak scale and produce a large lepton asymmetry at the QCD scale, which is then resonantly transformed into an abundance of the third state that acts as sterile neutrino dark matter. The minimality of this setup, known as Neutrino Minimal Standard Model ($\nu$MSM), makes it highly predictive. Earlier attempts to pin down the properties of the HNLs based on the requirement to simultaneously explain the neutrino masses as well as the baryonic and dark matter abundances were hampered by an incomplete understanding of the quantum kinetic equations describing the HNLs throughout cosmic history. We perform the first parameter scan of the $\nu$MSM in which this shortcoming has been overcome. We find that the $\nu$MSM provides a common explanation for all aforementioned phenomena only within a well-defined parameter space that is limited in all directions, with HNL masses kinematically accessible by the SHiP experiment as well as searches at the LHC and future lepton colliders. Further predictions for the HNL decay branching ratios, CP-violation, and lepton number violation (LNV) make the model highly testable, bringing a discovery of the common origin of neutrino masses and all matter in the Universe within reach of existing and planned experiments.
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All authors Marco Drewes, Yannis Georis, Juraj Klarić, Mikhail Shaposhnikov, Inar Timiryasov

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

Fermionic cosmic strings in dynamical Chern-Simons gravity

Stephon Alexander, Heliudson Bernardo and Shengyuan Zhang

We investigate topological defects produced by a chiral phase transition in a fermionic ultraviolet completion of dynamical Chern-Simons (dCS) gravity. The model contains a complex scalar field with a chiral Yukawa coupling to fermions. Below the chiral symmetry breaking scale, integrating out the gapped bulk modes produces a gravitational Chern-Simons coupling which, we argue, modifies cosmic string solutions from the phase transition. The resulting corrected string metric is supported by a generalization of the Callan-Harvey fermionic zero mode solution, in which the null current generated by these zero modes provides a mechanism for parity violation. In the weak-coupling and weak-gravity regime, we derive the leading order-reduced dCS correction to this exterior metric. We also discuss the effective action description for generic string configurations in dCS gravity. The gravitational Pontryagin term provides the anomaly inflow required to cancel the gravitational anomaly of the chiral worldsheet theory.
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Cosmology and Nongalactic Astrophysics

The Lumina Project: Morphology of Ionized Bubbles and Neutral Islands

Meredith Neyer, Aaron Smith, Ali Sadain et al. (+10 more)

The Epoch of Reionization is characterized by the nucleation, expansion, and percolation of ionized bubbles in the intergalactic medium. Interpreting emerging multi-wavelength observations from facilities such as JWST and next-generation 21 cm interferometers requires a detailed theoretical understanding of the 3D morphology of these HII regions and of the residual neutral structures that survive near the end of reionization. We analyze the geometry and physical properties of ionized bubbles and late-time neutral islands in the large-volume 500 Mpc$^3$ radiation-hydrodynamics simulation Lumina. We identify discrete structures with a 3D watershed method and measure their volumes, shape tensors, and internal gas properties. The volume-weighted bubble size distributions evolve substantially across the EoR: characteristic radii shift from Reff~1 cMpc at z>10 to Reff>100 cMpc by z< 6, while watershed-derived sizes exceed line-of-sight mean-free-path measurements by roughly a factor of 3 at intermediate redshifts. The bulk bubble population is predominantly prolate through most of the EoR. By z~6, however, the volume-weighted distribution of the triaxiality parameter T, which distinguishes flattened from elongated structures, becomes bimodal in the fiducial segmentation, with a sharp oblate peak near T~0.25 associated with a small number of very large bubbles during late percolation. The properties of bubble interiors are consistent with inside-out reionization, with median gas overdensities within bubbles decreasing from $\delta$~1 at z=15 toward the cosmic mean by z=6. Beyond a minimum near the resolution scale, the median internal UV radiation energy density increases with bubble size. The residual neutral islands at z< 6 peak in volume-weighted size near Reff~10 cMpc and remain predominantly prolate, consistent with anisotropic residual neutral structure near the end of reionization.
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All authors Meredith Neyer, Aaron Smith, Ali Sadain, Oliver Zier, Mark Vogelsberger, Teodora-Elena Bulichi, Xuejian Shen, Sonja M. Koehler, Volker Springel, Rahul Kannan, Rongrong Liu, Lars Hernquist, Changhyun Cho

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

Big Bang Nucleosynthesis as a Probe of First-Order Phase Transitions

Masanori Tanaka

Supercooled cosmological first-order phase transitions (FOPTs) generate a large temperature inhomogeneity due to their stochastic reheating process. If a baryon asymmetry production predates the FOPT and is conserved during it, the temperature contrast is transferred onto the baryon-to-photon ratio $\eta$ or the baryon-to-entropy ratio $Y_{B}$, producing an inhomogeneity probed by big bang nucleosynthesis (BBN). We extend a recent formalism for this effect by including the reheating dependence of the induced $Y_{B}$ fluctuations, combining the transition-time power spectrum from finite-bubble statistics with proton and neutron diffusion at the BBN epoch. When the nucleation temperature is in the range $10^{-2}\,{\rm GeV} \lesssim T_{n} \lesssim 10^{2}\,{\rm GeV}$, the precise measurement of deuterium abundances disfavors parameter regions with a sizable latent heat and a long transition duration at the $1 \sigma$ level. The bound weakens towards higher $T_{n}$ as diffusion becomes more efficient. We further show that this bound disfavors FOPT parameter regions compatible with the NANOGrav gravitational wave signal. This conclusion assumes that the baryon asymmetry predates the transition and that the fluctuation spectrum remains valid down to sub-bubble scales. Therefore, in such FOPT explanations of the NANOGrav signal, the baryon asymmetry cannot simply predate the transition. It can instead be generated after reheating or during the transition if the local baryon production tracks the local entropy injection. As a result, the timing of baryogenesis may be constrained by combining gravitational wave observations with light element abundance measurements.
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Cosmology and Nongalactic Astrophysics

Entropy applications in cosmology: spacetime thermodynamics, holographic dark energy, entropic gravity and beyond - a review

Emmanuel N. Saridakis, Giuseppe Gaetano Luciano, Andreas Lymperis et al. (+1 more)

Entropy has emerged as a key concept at the intersection of gravity, quantum theory, and cosmology, revealing deep connections between geometry, information, and thermodynamics. The realization that black holes are thermodynamic systems, characterized by an entropy proportional to their horizon area, has provided evidence that spacetime itself may possess a microscopic structure. Since then, entropy has acquired a central role across quantum field theory, holography, quantum gravity, and cosmology. In this review, we present a unified account of entropy in gravitational and cosmological contexts. We first survey entropy in gravitational systems, focusing on black-hole thermodynamics, entropy bounds, the holographic principle, entanglement entropy, and the area law, together with the main corrections and generalizations arising from quantum field theory, generalized uncertainty principles, modified statistics, and extended theories of gravity. We then discuss three conceptually distinct ways in which entropy is employed in cosmology. The first is through the spacetime-thermodynamics conjecture, in which gravitational dynamics emerge from thermodynamic relations applied to cosmological horizons, and generalized entropy forms consequently lead to modified cosmological evolution. The second is the holographic approach, in which entropy bounds constrain the vacuum energy of the Universe, giving rise to the holographic dark energy scenario and its various extensions. The third is entropic gravity, where gravity is interpreted as an emergent phenomenon of entropic origin, leading to interesting cosmological phenomenology. By reviewing the theoretical foundations and cosmological implications of these entropic frameworks, we aim to clarify the role of entropy, discuss open issues and outline directions toward a deeper thermodynamic and informational understanding of gravity and cosmology.
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All authors Emmanuel N. Saridakis, Giuseppe Gaetano Luciano, Andreas Lymperis, Eirini C. Telali

Cosmology and Nongalactic Astrophysics

JWST evidence for a sharp "Cosmic Daybreak" at z = 15

Jiashuo Zhang, Tom Broadhurst, Tzihong Chiueh et al. (+9 more)

Luminous young galaxies have been uncovered with relative ease by JWST, extending to z=14.5, so it is puzzling that deeper spectroscopy of fainter candidates now finds only interlopers. This redshift `ìmpasse" is underscored by the measured stellar ages of these high-z galaxies, which we show converge to zero by z=15, with a marked absence of earlier star-formation. Taken literally, such a late transition from the Dark Ages to luminous galaxies is unlike the gradual Cosmic Dawn of standard LCDM, but does confirm a key prediction of Wave Dark Matter, $\psi$DM, as a Bose-Einstein condensate. The de Broglie wave pressure resists gravity until a substantial Jeans mass of $4\times 10^9M_\odot$ is overcome at z$=$15, corresponding to a light boson $m_\psi=2.2_{-0.3}^{+0.4} \times 10^{-22}$eV, and similar to independent estimates from lensing anomalies and dwarf galaxies. Furthermore, the substantial luminosities of the highest redshift galaxies appear to converge to the initial Jeans scale of $\psi$DM, whereas LCDM predictions extend to lower luminosities and larger ages than observed. These contrasting predictions can be definitively tested as JWST observations accumulate, with diametric implications for Dark Matter as heavy particles beyond the Standard Model or ultra-light bosons motivated by the String Axiverse.
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All authors Jiashuo Zhang, Tom Broadhurst, Tzihong Chiueh, Hsi-Yu Schive, Keiichi Umetsu, Jose M. Diego, Paloma Morilla, Alvaro Pozo, Chian-Chou Chen, Jeremy Lim, Pablo G. Perez-Gonzalez, Rogier Windhorst

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

Dark Transport Erases Baryon Inhomogeneity from Supercooled Phase Transitions

Sudhakantha Girmohanta, Kohei Kamada, Yuichiro Nakai et al. (+1 more)

Supercooled phase transitions can generate observable gravitational waves, but their bubble dynamics may also imprint large spatial inhomogeneities in the baryon asymmetry. For phase transitions below the TeV scale, ordinary baryon diffusion can be too slow to erase such inhomogeneities before Big Bang Nucleosynthesis, potentially leading to stringent constraints from the observed light-element abundances. We show that this problem can be naturally avoided in darkogenesis scenarios, where the phase transition first generates an asymmetry in a dark-sector particle that is subsequently transferred to visible baryons. The dark-sector particle can travel over much larger distances than ordinary baryons before decaying, erasing the inhomogeneity before the baryon asymmetry is established. We derive the conditions for efficient erasure in both the diffusive and collisionless transport regimes and translate them into constraints on the dark-sector interactions. For a representative dark phase transition with a reheating temperature of $\mathcal{O}(1) \,\mathrm{GeV}$, $\beta/H \simeq 10$, and a dark-sector particle lifetime of $0.1\,\mathrm{s}$, we find that the inhomogeneity is efficiently erased for a viable range of the interactions. Importantly, baryogenesis before the phase transition is challenged both by dilution from strong supercooling and by the subsequent imprinting of spatial inhomogeneities. This points toward darkogenesis associated with the phase transition as a consistent framework, in which dark-sector transport erases the inhomogeneity before it is transferred to visible baryons.
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All authors Sudhakantha Girmohanta, Kohei Kamada, Yuichiro Nakai, Fumio Uchida

Cosmology and Nongalactic Astrophysics

Dark Matter-Induced Stellar Oscillations in the de Broglie Regime

Qiuyue Liang and Jeremy Sakstein

We investigate stellar oscillations driven by the time-dependent gravitational potential of ultralight dark matter (ULDM) in the de Broglie regime. The response is controlled by the ratio of the ULDM coherence time to the stellar mode damping time. When the field decoheres faster than the damping time, ULDM acts as a stochastic source that excites modes below a characteristic de Broglie frequency, while higher-frequency modes are suppressed. In the opposite, long-coherence regime, individual modes can be resonantly driven. Focusing on solar oscillations, we find a signal far below current sensitivity, and estimate that other stars are similarly unlikely to provide observable signals.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Quasinormal-mode redshifts of black holes in galactic halos with radial pressures

Che-Yu Chen, Hassan Hassanabadi and Soroush Zare

We investigate the black-hole quasinormal mode redshifts induced by a galactic dark-matter halo with nonvanishing radial pressure. The halo is described by an anisotropic fluid with a generalized density profile and a constant radial equation-of-state parameter $w$. We construct the corresponding static, spherically symmetric spacetime and study the resulting corrections to the unstable light ring and quasinormal-mode spectrum. For dilute halos and $w\neq -1$, the light-ring angular frequency and Lyapunov exponent acquire the same leading-order gravitational redshift, implying a universal shift of the real and imaginary parts of the quasinormal frequencies. The magnitude of this effect depends on both the halo structure and the radial pressure. This universal redshift relation holds not only in the case of $w=0$ that has been discovered in the literature but also in a much wider scenario, supporting its importance in black hole spectroscopy. On the other hand, the case $w=-1$ is qualitatively different: the factor that corresponds to the leading common redshift vanishes, the corrections are further suppressed by the hierarchy between the black-hole and halo scales, and the universal relation is broken, with the dominant contribution controlled by the inner halo profile. Our numerical computations of scalar-field quasinormal mode spectra confirm the analytic eikonal results.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.HE

A multi-telescope fit to the FRB population, allowing for FRB repetition

Jordan L. Hoffmann, Clancy W. James, Jason X. Prochaska et al. (+3 more)

Fast radio bursts (FRBs) are millisecond-duration radio pulses with extragalactic origins. A majority of FRBs have only had a single pulse detected from them; however, an increasing number have been identified as repeaters. Here we present a full redshift – dispersion measure ($z$-DM) analysis including a simple power-law model of repetition rates. We assume all FRBs are drawn from the same intrinsic population and fit these FRB population parameters using data from ASKAP, Murriyang (Parkes), DSA, FAST, MeerKAT and CHIME catalogue 1. We do not utilise data from CHIME catalogue 2 yet, as we cannot robustly identify all repeaters in the sample. We constrain the minimum repetition rate above $10^{39}$ erg to $R_{\mathrm{min}}=-4.23^{+1.10}_{-1.74}$ d$^{-1}$, the maximum repetition rate to $R_{\mathrm{max}} \gtrsim 1$ d$^{-1}$ and the repetition rate index to $R_{\gamma}=-2.20^{+0.12}_{-0.22}$. These parameters do not show significant correlation with any other FRB parameters. Our values are an improvement on existing results and are self-consistent with the DM distribution of CHIME and observed ratios of repeaters to non-repeaters across the sky. We also provide updated estimates of the FRB energy function and host galaxy parameters.
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All authors Jordan L. Hoffmann, Clancy W. James, Jason X. Prochaska, Ines Pastor-Marazuela, Kritti Sharma, Liam Connor

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

Correcting for Evidence Uncertainty in the Templated Background Search for the Stochastic Gravitational-Wave Background

Xiao-Xiao Kou, Argyro Sasli, Muhammed Saleem et al. (+1 more)

We report a new source of systematic bias in the Bayesian Templated Background Search (TBS) for the astrophysical stochastic gravitational-wave background. This bias arises from the statistical uncertainty in nested sampling evidence estimates at the segment level and persists even when the likelihood model accurately characterizes the data. Using an analytically tractable model and a frequency-domain mock data analysis with an astrophysically motivated binary black hole population, we show that this uncertainty coherently inflates the inferred duty cycle by up to an order of magnitude when millions of segments are accumulated. We propose a simple and efficient correction and demonstrate its effectiveness across all tested configurations. We also find that a search prior restricted to high optimal signal-to-noise ratio (SNR) misattributes intermediate-strength signals, while extending the prior to support weaker signals amplifies the evidence uncertainty. Both the correction and careful search prior design are essential for robust inference as TBS analyses scale to upcoming observing runs.
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All authors Xiao-Xiao Kou, Argyro Sasli, Muhammed Saleem, Vuk Mandic

Tuesday 22 September

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

Axions and the RR Lyrae Period-Luminosity Relation

Jeremy Sakstein and Djuna Croon

We investigate the impact of axions on the period-luminosity relation (PLR) of RR Lyrae stars. During the red giant branch phase, emission through the electron coupling cools the core, increasing its mass at ignition. The larger core produces more luminous horizontal-branch stars, systematically shifting the zero point of the RR Lyrae PLR toward brighter magnitudes. We model the RR Lyrae population of the globular cluster M3 using stellar evolution and pulsation calculations tailored to its age and composition, and compare the resulting synthetic $K_s$-band PLR with observations. For $\alpha_{26}\equiv 10^{26}g_{ae}^2/4\pi=0.5$, the axion-induced shift in the predicted PLR is comparable to the current uncertainty in the absolute M3 zero-point calibration.
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Cosmology and Nongalactic Astrophysics

Shape Degeneracies: the likely culprit for the differences between lens mass models of galaxy clusters

Liliya L.R. Williams, Derek C. Perera, Jori Liesenborgs et al. (+3 more)

Sky-projected mass distributions of galaxy clusters are widely used to constrain particle properties of dark matter, to magnify in flux and angular extent high redshift background galaxies, and to construct their luminosity function down to faint absolute magnitudes that are otherwise hard or impossible to reach. Obtaining accurate and precise mass maps of clusters is therefore of central importance for these studies. Yet, a visual inspection of any two mass maps of the same cluster shows that the shapes of their isodensity contours are often dissimilar in detail on <30kpc scales, and there is no simple relation connecting the two. These differences are due to systematic uncertainties in reconstructions, which are in turn due to lensing degeneracies. However, commonly known degeneracies, like the mass sheet degeneracy or the source position transformation cannot account for most of these differences, implying that more generalized shape degeneracies are responsible. In this paper we study shape degeneracies using an analytical approach. We conclude with three main takeaways: (i) Shape degeneracies are the likely cause of differences in the mass maps of cluster lenses recovered by different techniques. (ii) Shape degeneracies are significantly suppressed in regions of the lens plane that have tight groupings of lensed images. (iii) In clusters where image numbers are high, such as MACS J0416, their effect on time delays between images from the same source are generally small, of order 1%, but can reach ~10% for some multiply imaged background sources, affecting the determination of H_0.
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All authors Liliya L.R. Williams, Derek C. Perera, Jori Liesenborgs, Ashish K. Meena, Marceau Limousin, Leon R. Ecker

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

The lifetimes and properties of Little Red Dots in the AMBRA simulation

Patrick LaChance, Yihao Zhou, Aklant Kumar Bhowmick et al. (+6 more)

We identify and analyze the little red dots (LRDs) in the AMBRA cosmological hydrodynamic simulation, by producing mock observations of the galaxies and active galactic nuclei (AGN) between redshifts 5 and 8. We produce these mock observations with both a standard AGN emission model, and a “gas-enshrouded” model, and find that the presence of a gas-enshrouded AGN is instrumental to the reproduction of dim LRDs (F444W magnitude $>$ 26.0). We find a steeper decrease in LRD density between $z=5$ and $z=8$ within AMBRA than seen in observations, resulting in a relative underproduction of LRDs beyond $z\sim6$ in AMBRA. With the addition of unresolved AGN variability, the decline with redshift flattens, and the LRD redshift evolution in AMBRA becomes broadly consistent with other theoretical datasets, and closer to that seen in observations. We find that the LRDs in AMBRA are pre-existing black hole–galaxy systems that are undergoing an LRD phase, selected primarily by the brightness of the AGN relative to its host. While the exact duration of these LRD phases is not possible to determine due to the unresolved nature of the AGN environment, we use the available time-series data to place limits on the lifetimes of the LRDs in AMBRA. We find that the vast majority of LRDs in AMBRA have lifetimes between $\sim3$ and $\sim 300$ Myr with LRD lifetime increasing with both black hole and host galaxy mass. The lower mass LRDs are more dependent on housing a gas-enshrouded AGN, and have shorter lifetimes ($\rm \sim30~Myr$). The higher mass LRDs are less sensitive to their AGN environment, but require more compact host galaxies, and have longer lifetimes ($\rm \sim100~Myr$).
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All authors Patrick LaChance, Yihao Zhou, Aklant Kumar Bhowmick, Rupert A.C. Croft, Tiziana Di Matteo, Laura Blecha, Fabio Pacucci, Paul Torrey, Simeon Bird

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

The birth and fate of stellar clumps in super-early galaxies

B. Das, A. Ferrara, A. Pallottini et al. (+2 more)

(Abridged) JWST has revealed extremely compact stellar clumps in galaxies at z>6, but their formation mechanism and subsequent evolution remain uncertain. We investigate whether such systems can form in-situ through the fragmentation of an early galactic disk and how stellar feedback regulates their properties. We perform a suite of radiation-hydrodynamical simulations of an isolated galaxy ("Ninfea_blu"), with $\rm M_{vir}=1.5\times10^{10} M_\odot$, evolved for 100 Myr from z=16 to 12.5 with a maximum spatial resolution of 3.6 pc. In all cases, the gas rapidly forms a rotationally supported disk, reaches a peak star formation rate of $10-15\rm M_\odot yr^{-1}$, and fragments into dense stellar clumps. Toomre-unstable regions ($Q_{\rm gas}<1$) appear before the onset of star formation, and the first stellar structures form preferentially within these regions, supporting a Toomre-like gravitational fragmentation pathway.The clumps have stellar masses of $10^6-2\times10^8\,M_\odot$, effective radii of 7-50 pc, and surface densities of $0.2-3\times10^4\rm M_\odot pc^{-2}$, overlapping much of the parameter space occupied by observed z>6 clumps. Feedback reduces the cumulative stellar mass by 30-40%, lowers the gas mass retained within clumps by ~1 dex, and suppresses their high-mass tail without preventing their initial formation. Clumps subsequently migrate, interact, undergo tidal stripping, and disperse. The clump mass function produces a power law slope of -1.88, which aligns closely with observations. Moreover, their contributions to the stellar mass and intrinsic UV luminosity decline from 0.41 and 0.40 at 20 Myr to 0.13 and 0.10 at 100 Myr, respectively. We conclude that fragmentation of compact, gas-rich disks provides a viable origin for many of the dense stellar systems observed in the early Universe, while feedback and internal dynamics primarily regulate their growth and fate.
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All authors B. Das, A. Ferrara, A. Pallottini, E. Ntormousi, M. Kohandel

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

The Simons Observatory: Commissioning of the Mid-Frequency Small Aperture Telescopes

Kathleen Harrington, Remington Gerras, Nicholas Galitzki et al. (+88 more)

The Simons Observatory (SO) is a cosmic microwave background (CMB) survey experiment observing from an altitude of 5,200 m in the Atacama Desert in Chile. The SO Small Aperture Telescopes (SATs) will cover six spectral bands between 30 and 280 GHz primarily to search for evidence of primordial gravitational waves in the large angular scale $B$-modes of the CMB polarization. The first two Mid-Frequency (MF) SATs, operating in the 90 and 150 GHz frequency bands, began commissioning observations in late 2023, and we present the results of those observations here. Each MF SAT operates with approximately 9,400 biased transition-edge sensors (TES) at 1 mm of precipitable water vapor (PWV), representing a typical 80% yield. Planet observations confirm the telescope optics performance, calibrate the instrument response, and measure the end-to-end optical efficiency of the SATs. The realized instrument efficiencies are within the range expected based on instrument model predictions. In nominal observing conditions, the noise equivalent temperatures from both telescopes combined are $2.4~\mathrm{\mu K_{CMB}\sqrt{s}}$ at 90 GHz and $3.2~\mathrm{\mu K_{CMB}\sqrt{s}}$ at 150 GHz, substantially outperforming the baseline instantaneous sensitivity targets for the observatory.
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All authors Kathleen Harrington, Remington Gerras, Nicholas Galitzki, Samuel Day-Weiss, Yoshinori Sueno, Thomas Alford, Michael J. Randall, Kyohei Yamada, Maximiliano Silva-Feaver, Kevin Crowley, Shunsuke Adachi, Alexandre E. Adler, Prakamya Agrawal, Simone Aiola, David Alonso, Kam Arnold, Susanna Azzoni, Andrew Bazarko, Sanah Bhimani, Simon Biquard, Bryce Bixler, Josh Borrow, Michael L. Brown, Erminia Calabrese, Yuji Chinone, Steve K. Choi, Nadia Dachlythra, Mark Devlin, Simon Dicker, Peter N. Dow, Shannon M. Duff, Jo Dunkley, Rolando Dunner, Daniel Dutcher, Hamza El Bouhargani, Josquin Errard, Allen Foster, Ken Ganga, John Groh, Yilun Guan, Jon E. Gudmundsson, Saianeesh Haridas, Masaya Hasegawa, Matthew Hasselfield, Shawn W. Henderson, Carlos Hervías-Caimapo, Adam D. Hincks, Renée Hložek, Johannes Hubmayr, Bradley R. Johnson, Yutaro Kasai, Brian Keating, Ben Keller, Theodore Kisner, Brian J. Koopman, Akito Kusaka, Adrian Lee, JB Lloyd, Anto Lonappan, Marius Lungu, Aashrita Mangu, Michael McCrackan, Jeff McMahon, Jenna Moore, Thomas W. Morris, Hironobu Nakata, Federico Nati, Laura Newburgh, David V. Nguyen, John Orlowski-Scherer, Lyman Page, Ioannis Paraskevakos, Tristan Pinsonneault-Marotte, Erik Rosenberg, Yuki Sakurai, Goureesankar Sathyanathan, Thomas P. Satterthwaite, Yudai Seino, Elle Shaw, Sara M. Simon, Suzanne T. Staggs, Junna Sugiyama, Junya Suzuki, Satoru Takakura, Osamu Tajima, Alex Thomas, Daniel B. Thomas, Tran Tsan, Eve Vavagiakis, Yuhan Wang, John Wilson

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

Waiting in the wings: extended emission GRBs from high latitude emission and jet expansion

Isabelle Worssam, Benjamin P. Gompertz and Hendrik J. van Eerten

The process powering extended emission (EE) Gamma Ray-Bursts (GRBs) from compact object mergers is a debated problem due to their observed prompt emission timescales of 10 to 100s, far in excess of the expected accretion timescales following a binary neutron star (BNS) merger. Here, we present an analytical thin shell structured jet model designed to alleviate this tension. We show that a changing jet structure in which early emission is produced by a high Lorentz factor narrow, structured jet and later emission comes from a wider, lower Lorentz factor tophat-like jet can successfully reproduce the EE GRB phenomenology. All emitting shells are powered by a $0.1$ $M_{\odot}$ accretion torus and launched within a time window of 2s after merger. Spatially-resolved opacity checks confirm that our emission sites remain optically thin, in part due to the spectral softness associated with EE. We present light curves from our model compared to representative EE bursts detected by Swift: GRBs 211211A, 211227A and 060614. While our light curves provide good matches to the data, our spectra do not evolve fast enough when compared to the well-measured spectral evolution observed in GRB 211211A. We discuss an update to the model incorporating inherent spectral evolution in the shells as future work. We also show a parameter exploration of the model and identify a parameter range within which standard short GRB-like light curves could be produced, showcasing the ability of the model to produce short bursts with and without EE.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

The universe as a superconductor: How to search for a photon mass

Andrei Gruzinov, Anson Hook and Junwu Huang

We revisit the bounds on the photon mass when it arises from an Abelian Higgs mechanism rather than a Proca term. Because the higgs is necessarily millicharged and light, the phase of the theory (Meissner, vortex, or symmetry-restored) depends on the ambient magnetic field, so the photon mass an experiment measures depends on the environment it is performed in. We classify existing experiments by the phases in which they apply, in analogy with Type I and Type II superconductors. For Type I photon masses, magnetic fields in galaxies and the intergalactic medium can restore the symmetry everywhere, allowing a vacuum photon mass as large as $0.3 \,{\rm MeV}$. Regions of photon mass as large as $10^{-5}\, {\rm eV}$ could be present in the Universe, and measurement of frequency dependent optical depth can potentially reveal these regions. For Type II photon masses, we show that the strongest constraints mainly arise from the requirement that the galactic dynamo generates the observed magnetic fields, which we derive by generalizing magnetohydrodynamics to a nonzero photon mass. Since the terrestrial magnetic field restores the symmetry in much of the remaining parameter space, laboratory searches performed inside large magnetically shielded volumes, or in space, could probe photon masses invisible to any experiment on Earth. Measurements of distant light sources, in particular, fast radio bursts, also offer unique sensitivity to parameters invisible to lab experiments.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

The First Blind Survey of Intervening NaI Absorbers: Incidence and Cosmic Evolution with DESI

Abhijeet Anand and Sowgat Muzahid

We present the first blind statistical survey of intervening NaI absorbers over the last $\simeq3$~Gyr using quasar spectra from the Dark Energy Spectroscopic Instrument Data Release~1. We identify 3636 NaI D doublets at $0.01\lesssim z_{\rm abs}\lesssim0.27$ along 214,035 quasar sightlines. We quantify the survey selection function through end-to-end injection–recovery tests and estimate the residual contamination from visual inspection. The completeness reaches 50% at a rest-equivalent width of the NaI $\lambda5891$ line, $W_{5891}\simeq0.95$ Angstrom, and the catalog-weighted purity is $\simeq77\%$. For the fiducial sample with $0.95<W_{5891}<3.5$ Angstrom, we measure the equivalent-width distribution ($f(W_r)$), absorber incidence ($dN/dX$), and cosmic NaI mass density ($\Omega_{\rm Na\,I}$). From $z\simeq0.25$ to $z\simeq0.03$, $dN/dX$ rises by a factor of $\simeq3.4$ in both rest-equivalent-width subsamples, split at the median $W_{5891}=1.41$ Angstrom, while $\Omega_{\rm Na\,I}$ increases by a similar factor. This corresponds to a smooth increase in the product of the comoving number density of NaI-absorbing hosts ($n_{\rm com}$) and the cross-section of the NaI-bearing gas ($\sigma_{\rm eff}$) with cosmic time. The similar evolution of $\Omega_{\rm Na\,I}$ and $dN/dX$ indicates little change in the mean measured NaI column density per absorber. We also find preliminary evidence that NaI absorbers are associated with foreground galaxies at relatively small projected separations and that their quasar sightlines are redder than matched controls. These results support a picture in which NaI traces dense neutral gas in and around galaxies. Dedicated galaxy surveys and CGM/ISM simulations can test the inferred incidence and cross-section, while spectral stacking can probe the associated gas and dust.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Tachyonic particle production in strongly supercooled phase transitions

Mateusz Kulejewski, Bogumila Swiezewska and Jorinde van de Vis

In strongly supercooled cosmological phase transitions, which generically lead to strong, observable gravitational-wave backgrounds, the scalar field typically transitions to a value well below the minimum of its potential. We study particle production caused by the subsequent evolution of the field. Because some modes feature temporarily tachyonic masses, they can be efficiently produced, and a significant fraction of the energy density released in the phase transition can get converted to particles rather than gradient energy. This has consequences for the shape and amplitude of the gravitational-wave spectrum caused by the interactions in bubbles and sources a new, high-frequency signal. Moreover, it affects the bubble expansion velocity and equation of state, which can facilitate the formation of primordial black holes.
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Cosmology and Nongalactic Astrophysics

To USR or not to USR: An effective description of two-field dynamics

Samuel Sánchez López and Eemeli Tomberg

Single-field models of inflection point inflation experience a phase of ultra-slow roll (USR), leading to amplified curvature perturbations. Recently, Lorenzoni et al. modified the scenario by adding a light spectator field, showing that it ruins USR by setting a floor for the first slow-roll parameter $\epsilon$. Mixing with isocurvature perturbations still amplifies the curvature power spectrum. We offer an alternative point of view, arguing that the inflaton still undergoes effective USR. The spectator lifts the potential by a constant amount, and the inflaton perturbations follow single-field dynamics in the lifted inflection point potential, decoupling from the spectator perturbations. Mode mixing only affects the power spectrum dip, making it milder. We demonstrate this effective single-field behavior numerically for example models. Our results offer a simple way to study the models' parameter dependence.
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Cosmology and Nongalactic Astrophysics

Data-driven Galaxy Population Prior for Photometric Redshifts

Nikolas Frediani, Daniel Gruen, Luca Tortorelli et al. (+1 more)

Stage-IV cosmological surveys rely on well-characterised photometric redshift distributions for constraining cosmological models, yet the projected weak lensing requirements are about an order of magnitude more accurate than current state-of-the-art methods. Any photometric redshift inference depends - explicitly or implicitly - on a prior over galaxy SEDs, luminosities, and redshifts. In this paper, we develop a purely data-driven approach for modelling the galaxy population prior based on learning the distribution of galaxy SEDs and evaluate its induced systematic uncertainties for photometric redshift calibration. Under controlled conditions, we build a template-free model for galaxy SEDs with minimal physical assumptions and assess how well it can reproduce the colour-redshift relation. We train a generative model on a realistic population of noisy mock galaxy spectra, simulated using the GalSBI-SPS galaxy population model, to learn the joint distribution of intrinsic spectra, luminosities, and redshifts. We employ a probabilistic autoencoder that compresses spectra into a low-dimensional latent space and performs neural density estimation with a normalising flow. The autoencoder can reconstruct the shape of galaxy spectra with Gaussian noise of standard deviation $\sigma$ to $\sim0.1\,\sigma$ of the ground truth, thereby building a model for noiseless SEDs from noisy spectra only. We construct colour-selected tomographic bins with a self-organising map and compare the predicted mean redshift. We find that deviations in each bin are smaller than the per-mille Stage-IV requirements, with $| \Delta \langle z \rangle |\lesssim 0.0007 (1+z)$. This work serves as a proof-of-concept that generative models can learn the prior of galaxy observations accurately enough for upcoming surveys under controlled conditions.
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All authors Nikolas Frediani, Daniel Gruen, Luca Tortorelli, Jamie McCullough

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

A Simple Dark Matter Model to Explain the LZ Event and Galactic Center Excess

Caleb Gemmell, Dan Hooper and Gordan Krnjaic

We propose that the dark matter (DM) is a pseudo-Dirac fermion with a mass of approximately $20-100$ GeV that couples inelastically to the Standard Model through a hadrophilic spin-1 mediator, $V$, the gauge boson of spontaneously broken baryon number. The two DM eigenstates, $\chi_{1}$ and $\chi_2$, acquire approximately equal abundances after thermal freeze-out and are depleted through the processes $\chi_1 \chi_1 \to VV$ and $\chi_2 \chi_2 \to VV$. Although the heavier state is unstable, for a mass splitting below the electron-positron threshold and sufficiently small mass mixing with the $Z$ boson, its lifetime can exceed the age of the universe, allowing both states to remain approximately equally abundant in the Galactic halo. For a thermal-relic annihilation cross section, this model can produce a signal that is consistent with the observed features of the longstanding Galactic Center Gamma-Ray Excess (GCE). If $\delta \sim 1000$ keV, the same parameter space that explains the GCE can also explain the LZ event through exothermic $\chi_2 \to \chi_1$ downscattering off xenon nuclei.
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Cosmology and Nongalactic Astrophysics

Constraining Inflation with Little Red Dots

Dionysios Karagiannis and P. Daniel Meerburg

Primordial non-Gaussianity is a direct probe of the physics of inflation. The tightest bounds still come from the cosmic microwave background, but large-scale structure is rapidly catching up: its intrinsically three-dimensional maps contain far more modes, provided the tracer combines large volume, high redshift, strong bias and sufficient number density. The Little Red Dots (LRDs) discovered by JWST plausibly offer all four. Inspired by recent work on BAO measurements using LRDs we forecast the joint galaxy power spectrum and bispectrum of a $14{,}000\,{\rm deg}^2$ LRD spectroscopic survey over $4<z<9$, marginalising over $32$ nuisance parameters and including the non-Gaussian bispectrum covariance. We find $\sigma(f_{\mathrm{NL}}^{\mathrm{loc}})=0.32$, $\sigma(f_{\mathrm{NL}}^{\mathrm{equil}})=32$ and $\sigma(f_{\mathrm{NL}}^{\mathrm{orth}})=10$, improving on Planck by factors of $16$, $1.5$ and $2.3$. The local bound lies a factor of three below the $\sigma(f_{\mathrm{NL}}^{\mathrm{loc}})\simeq1$ threshold that separates broad classes of single- and multi-field inflation. LRD clustering therefore has the potential to become an important probe of inflation, and makes a strong case for future wide-field near- to mid-infrared spectroscopy.
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Cosmology and Nongalactic Astrophysics

Gravitational-Susceptibility Dip Behind DESI's results: Addressing the Phantom Crossing by Local limit of Nonlocal Gravity

Aria Hemmatian, Yahya Mohammadi, Javad Tabatabaei et al. (+1 more)

The second data release of the Dark Energy Spectroscopic Instrument (DESI), based on more than fourteen million galaxies and quasars, prefers a dark energy component whose equation of state is dynamical. In the simplest two-parameter description of this behavior, the Chevallier–Polarski–Linder (CPL) parametrization, the data favor the quadrant $w_0>-1$, $w_a<0$, which implies that the equation of state crosses the phantom divide $w=-1$ at a redshift $z\simeq0.4$. We show that the local limit of nonlocal gravity, a teleparallel extension of general relativity governed by a scalar function called gravitational susceptibility $S(x)$, offers a natural explanation. In this model a cosmological constant is not allowed; dark energy is necessarily dynamical. The phantom crossing seen by an observer is an effective phenomenon generated by the time evolution of $S(z)$. We establish a correspondence: to every general-relativistic dark energy model with equation of state $w(z)$, there corresponds a modified TEGR cosmology with $w=-1$ and a suitable susceptibility $S(z)$ that are indistinguishable at the level of the background expansion. We construct the susceptibility functions that reproduce the CPL behavior favored by DESI data, and we confront the model with the combined CMB,BAO, and SNe data using Boltzmann solver codes. The recovered susceptibility displays a characteristic low-redshift dip with depth $\beta = -0.025 \pm 0.007$ at $z\simeq 0.4 $, and its derivative changes sign at a redshift equal to the phantom-crossing epoch.
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All authors Aria Hemmatian, Yahya Mohammadi, Javad Tabatabaei, Shant Baghram

Cosmology and Nongalactic Astrophysics

Bayesian Galaxy Asymmetry

Mathieu Perron-Cormier, Kristine Spekkens, Nathan Deg et al. (+2 more)

Galaxy asymmetry is an efficient way to characterize galaxy morphology in atomic hydrogen 21 cm emission detections. We propose a novel Bayesian approach to calculate the probability of an underlying squared differences asymmetry in a noisy detection. This approach has a number of advantages, including the recovery of low asymmetry values where prior noise corrections failed. More importantly, our approach provides robust uncertainties on the asymmetry, enabling a wide variety of statistical studies of galaxy populations. This method is generalized for convolved noise measures. We validate our method using a convergence test. Finally, we show how, when applied to the untargeted HI survey WALLABY, our method nearly triples the number of reliable measurements relatively to the previous state-of-the-art technique. This Bayesian approach to measure asymmetry will therefore further unlock the statistical power of widefield galaxy surveys.
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All authors Mathieu Perron-Cormier, Kristine Spekkens, Nathan Deg, Lawrence M. Widrow, Marcin Glowacki

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

Big Bang Nucleosynthesis Confronts Domain Walls and First-Order Phase Transitions as the Pulsar Timing Array Explanations

Fatemeh Elahi, Diego Fortini, Yann Gouttenoire et al. (+2 more)

Pulsar timing arrays (PTAs) have detected a nanohertz gravitational-wave background, often attributed to annihilating domain walls (DWs) or first-order phase transitions (FOPTs). Their reheating imprints fluctuations in the baryon-to-photon ratio. These so-called baryon isocurvature fluctuations $S_B$ survive until Big Bang Nucleosynthesis, whose yields depend nonlinearly on it. Modest $S_B$ fluctuations can therefore alleviate the current deuterium tension in parts of the PTA preferred regions and therefore strengthen their interpretation. Overabundant DWs and too strong FOPTs overproduce $D/H$ and are ruled out.
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All authors Fatemeh Elahi, Diego Fortini, Yann Gouttenoire, Nicholas Leister, Pedro Schwaller

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

Dark Diffraction at LZ from a Screened Neutral Composite Baryon

Hyunjoo Jung and Seong Chan Park

The LUX-ZEPLIN (LZ) experiment recently reported a nuclear-recoil-like candidate at $E_R=248\pm23_{\rm stat}\pm23_{\rm sys}$ keV. We show that such an energetic recoil can arise from the elastic form factor of composite dark matter, without invoking an inelastic mass splitting or a boosted population. A neutral baryon of $N$ dark quarks can have a charge form factor that is suppressed at low momentum transfer but recovers at higher momentum transfer, providing a momentum-space band-pass filter. Modeling the form factor with one Gaussian per charged constituent species, we prove that two terms cannot produce a hard recoil spectrum and find that three yield too few events in the LZ signal window, while four suffice. A confining $SU(4)_D\times U(1)_D$ gauge theory provides a concrete realization through a neutral bosonic baryon made of four dark quarks. For a 200 GeV benchmark normalized to one accepted event, we predict approximately 1.5 true recoils beyond the current LZ region of interest. The form factor also produces diffraction nodes at fixed momentum transfers, placing them at recoil energies that scale as $1/m_A$ across target nuclei.
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Cosmology and Nongalactic Astrophysics

Probing the Mass–Redshift Dependence of Binary Black Holes and its Implications for $H_0$ with GWTC-5.0

Yang Liu, Puxun Wu, Jun-Jie Wei et al. (+1 more)

The mass and redshift distributions of merging binary black holes (BBHs) bear imprints of their astrophysical formation channels. Whether the BH mass distribution evolves with redshift, however, remains an open question. In this paper, we employ copula functions, which describe the dependence between variables independently of their marginal distributions, to probe the dependence structure between the primary mass and the redshift of BBH mergers. We construct five population models by coupling the marginal distributions of primary mass and redshift with the Gaussian copula, the Clayton copula, or one of its three rotations, and we constrain their hyperparameters using 235 BBH events from GWTC-5.0. For comparison, we also adopt a baseline model in which the primary mass and redshift are assumed independent. Among the copula-based models, only the model with the $180^\circ$ rotated Clayton copula, which couples higher primary masses preferentially with high redshifts, exhibits evidence for a nonzero correlation, with its copula parameter deviating from the independence limit at more than $1\sigma$ significance. Importantly, the constraints on the Hubble constant ($H_0$) derived from these models are mutually consistent within the $68\%$ confidence level; the baseline model yields $H_0=74.3^{+13.7}_{-19.6}~\mathrm{km\ s^{-1}\ Mpc^{-1}}$, indicating that allowing for a mass–redshift dependence does not significantly bias the $H_0$ inference with the current dataset. Bayesian model comparison favors the baseline model over all copula-based alternatives, with log-Bayes factors corresponding to weak to moderate evidence against the latter on the Jeffreys scale. Our results thus imply that the current GWTC-5.0 sample remains consistent with no redshift evolution of the primary mass distribution over the redshift range probed.
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All authors Yang Liu, Puxun Wu, Jun-Jie Wei, Xue-Feng Wu

Cosmology and Nongalactic Astrophysics

HierArchical Wavelet Coefficients on the Sphere (HAWCS): the Scattering Transform on Spherical Maps

Arefe Abghari, Lukas T. Hergt, Douglas Scott et al. (+1 more)

Extracting Gaussian information from data is well understood, but characterizing non-Gaussianity is challenging. We introduce HAWCS, a healpy-based Python package for efficiently computing wavelet scattering transform coefficients from full-sky maps. These coefficients provide compact summary statistics that are sensitive to higher-order structure and interactions across angular scales. We test the implementation on controlled Gaussian and non-Gaussian fields and demonstrate its computational efficiency. We then apply HAWCS to thermal Sunyaev-Zeldovich maps derived from Planck observations and four simulations, quantifying and comparing their higher-order statistical properties. We also use the method to expose the signatures of gravitational lensing in cosmic microwave background (CMB) temperature maps. These results demonstrate that HAWCS is a practical tool for validating component-separation pipelines and cosmological simulations, and a promising summary statistic for characterizing non-Gaussian structures beyond the power spectrum. These coefficients could also be used to constrain or generate simulated maps that reproduce the same statistical features of real data.
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All authors Arefe Abghari, Lukas T. Hergt, Douglas Scott, Raelyn M. Sullivan