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Physics Astrophysics Cosmology and Nongalactic Astrophysics

astro-ph.CO Watch Cosmology and Nongalactic Astrophysics

Tuesday 15 September

Cosmology and Nongalactic Astrophysics

Infrared Universality of Scalar Induced Gravitational Waves Beyond Second Order

Chen Yuan

Primordial black hole dark matter is formed from the collapse of enhanced primordial density fluctuations. The formation of primordial black holes is accompanied by scalar induced gravitational waves whose infrared scaling only depends on the equation of state, $w$, of the background at leading order. Establishing whether this characteristic scaling remains robust under corrections of arbitrary perturbative order, including in the presence of non-Gaussianities, requires a physical understanding of the infrared scaling. In this work, we provide such a physical interpretation. We find that the stress of sound waves with nearly equal frequencies produces a slow beat. Although the incoming waves oscillate rapidly, this slow beat continues to source the long wavelength tensor perturbation before its horizon entry, thus generating an infrared scaling that only depends on the expanding background. We show that higher order interactions generate freely propagating waves that finally lead to the same slow beat deep inside the horizon. Since non-Gaussianities would not change the speed of the freely propagating waves, they do not modify the infrared scaling. As the source with a slow beat has enough time to accumulate before the horizon entry of the infrared tensor mode, it records the background expansion and thus the infrared scaling could provide a robust probe of the cosmological equation of state.
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Cosmology and Nongalactic Astrophysics

Resolving 3 Exotic Hyperbolic-Umbilic Lensing Configurations in the "Cosmic Mantis": An Exploration of RXJ0437.1+0043 with JWST

Catherine Cerny, David J. Lagattuta, Keren Sharon et al. (+12 more)

We present an updated strong lensing model for the galaxy cluster RXJ0437.1+0043 (z=0.285) using new JWST NIRCam imaging in four pass-bands. The cluster field notably displays at least three separate gravitationally lensed galaxies in hyperbolic-umbilic (H-U) configurations, which in the JWST imaging show exquisitely resolved stellar clumps at scales as small as 0.04”. We identify 13 new systems of multiply-imaged lensed galaxies and determine the redshifts for two sources based on archival spectroscopic observations. We also identify over 50 individually resolved substructure clumps in the multiple images of eight galaxies and add them into the lens model, for a total of 275 positional lensing constraints between all 26 lensed sources used in the model. We investigate the impact of different modeling choices on our results. In the final lens model, we reproduce the observed multiple images with a precision of 0.23” , and achieve 0.13” specifically for the H-U systems. We estimate a total enclosed mass in the cluster's strong lensing regime of M(<110 kpc) ~ 8.2 x 10^13 Msun, reconstruct the source images of the most highly magnified galaxies, and measure time delays in the most magnified, morphologically detailed systems. The isotropic lensing effect from the H-U configurations enables future detailed studies of the properties of their source galaxies, and the number and spatial density of additional constraints improve the model's ability to detect dark matter substructures within the cluster core.
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All authors Catherine Cerny, David J. Lagattuta, Keren Sharon, Gourav Khullar, Benjamin Beauchesne, Alastair C. Edge, Mathilde Jauzac, Marceau Limousin, Guillaume Mahler, Lukas J. Furtak, Leo Fung, Qiuhan He, Richard J. Massey, Ashish K. Meena, Adi Zitrin

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

Optimising instrument concepts with Machine Learning: Application to CMB spectral distortion experiments

Xavier Coulon, Nabila Aghanim and Bruno Maffei

Understanding how instrumental and mission parameters affect the ability to measure faint astrophysical signals is a key challenge in the design of future experiments. This is particularly relevant for CMB spectral distortions, whose weak signals are affected by both instrumental effects and astrophysical foregrounds. We develop a method to explore and optimise the multidimensional parameter space of an astronomical instrument, and apply it to CMB spectral distortion measurements using the FOSSIL mission concept. We combine a dedicated sky model with a realistic instrument model and use Fisher forecasts to assess measurement capabilities of the simulated instrument. Decision-tree-based regression models are then used to learn the non-linear mapping between instrumental parameters and the predicted signal-to-noise ratios of the sky observables. Random Forest and gradient boosting models accurately reproduce the forecasted measurement performance. SHAP values are used to interpret the impact of instrumental parameters on the measurement. The temperature of the warmest instrumental component is found to be the dominant parameter for all three observables, highlighting the importance of limiting internal emission and operating the instrument at cryogenic temperatures. Frequency coverage is also highly influential, revealing a trade-off between spectral coverage and instrumental sensitivity. The proposed optimisation method provides a fast and interpretable approach to explore high-dimensional instrumental parameter spaces and identify parameters that most strongly influence the scientific performance of an experiment. To the best of our knowledge, this work represents the first application of machine-learning methods to the global optimisation of an astronomical instrument and can readily be extended to other astronomical instruments and mission concepts.
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Cosmology and Nongalactic Astrophysics

On the cosmic previrialization

Shubhadip Bera and Michał J. Chodorowski

Non-linear gravitational evolution affects the growth of density and velocity fluctuations, and leads to previrialization effects before virialized structures are formed. Therefore, understanding and quantifying the leading nonlinear corrections to the corresponding variances is crucial for describing the departure from linear structure formation. We calculate the first nonlinear correction to the variance of the cosmic density and velocity fields. We analyze the 1-loop contributions associated with the second and third order perturbative kernels of both the density and velocity-divergence fields. The relevant forms of the third-order kernels $F_3(\vec{k},\vec{q},-\vec{q})$ for density, and $G_3(\vec{k},\vec{q},-\vec{q})$ for velocity divergence, are clearly non-symmetric under exchange of $\vec{k}$ with $\vec{q}$. However, the calculation of the variance involves a symmetric double integral of these variables, so in this particular case the kernels can be additionally symmetrized. We therefore explicitly symmetrize these kernels $F_3$ and $G_3$, and express them as functions of the two scalar variables: the cosine of the angle between the two wavevectors and a symmetric function of their magnitudes. This representation enables us to identify and isolate the terms which are divergent before performing the angular integration, and to show their cancellation between the second- and third-order terms. The divergent contribution from $P_{\delta 22}\,$ to the one-loop power spectrum cancels exactly that arising from $P_{\delta 13}$ . Angularly averaged divergence-free part of $F_3$ turns out to be remarkably close to a constant. We found that the corresponding coefficient of the leading-order correction is confined to a remarkably narrow interval of 4007/2205 to 4063/2205 $(\simeq 1.817 \leq C \leq 1.843)$, for any form of the linear power spectrum.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

JADES: Dynamical Measurements of Dark Matter Halo Masses at $z \approx 7$ Using Galaxy Pairs

Zihao Wu, Daniel J. Eisenstein, Benjamin D. Johnson et al. (+13 more)

We present dynamical measurements of dark matter halo masses at $z\approx7$ using galaxy pairs. Galaxy pairs in the early Universe are usually in their first infall, before substantial orbital evolution or phase mixing. Their relative velocities closely trace the halo mass, especially when the pair separation is near the halo virial radius. In the TNG100 simulation, we find that dynamical mass estimators can recover halo masses with an intrinsic scatter of $\sim$0.2 dex. We apply this method to 10 pair systems at z=6-8 with [O III] spectroscopy from the JWST Advanced Deep Extragalactic Survey (JADES). We infer the stellar-to-halo mass relation while marginalizing over projection effects, measurement uncertainties, and intrinsic scatter. We find a mean halo mass of $\log\,(M_{200}/M_\odot)=11.06\pm0.21$ at $\log\,(M_{*}/M_\odot)=9$. These galaxies do not appear to inhabit unusually massive halos. Our results instead indicate a high stellar-to-halo mass ratio, corresponding to an integrated star formation efficiency of $5^{+3}_{-2}\%$, about twice the TNG100 prediction, although the current statistical significance is limited. Future observations with larger samples will tighten these constraints and directly examine whether enhanced star formation efficiency drives the overabundance of luminous galaxies at cosmic dawn.
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All authors Zihao Wu, Daniel J. Eisenstein, Benjamin D. Johnson, Lars Hernquist, Sandro Tacchella, Brant E. Robertson, Santiago Arribas, Andrew J. Bunker, Qiao Duan, Jakob M. Helton, Zhiyuan Ji, Dávid Puskás, Pierluigi Rinaldi, Fengwu Sun, Hannah Übler, Yongda Zhu

Cosmology and Nongalactic Astrophysics

A reanalysis of the megamaser Hubble constant: from spot catalogues to peculiar velocities

Richard Stiskalek and Harry Desmond

The Hubble tension motivates careful scrutiny of the redshift-independent distances underpinning the local distance ladder. Water megamasers afford a purely geometric distance from orbital dynamics in an accretion disc. For five of the six Megamaser Cosmology Project (MCP) galaxies, we present a Bayesian forward model that infers the angular-diameter distance and warped Keplerian disc parameters jointly from the very long baseline interferometry quasi-observables: maser spot positions, velocities, and accelerations. We then constrain $H_0$ from these distances and the host redshifts, including a physical distance prior, modelling the galaxy sample selection and testing a linear and a non-linear peculiar-velocity reconstruction. Accounting for peculiar velocities with the non-linear Manticore reconstruction, we infer $H_0 = 71.6 \pm 3.7$ km/s/Mpc, where the uncertainty is statistical. Relative to ignoring peculiar velocities, the linear and non-linear reconstructions lower $H_0$ by $0.8$–$1.4$ and $1.6$–$2.1$ km/s/Mpc, respectively, whereas changing the selection variable alters it by less than $1$ km/s/Mpc. We analyse the sixth galaxy, NGC 4258, separately. Modelling its disc as eccentric and quadratically warped, we infer an angular-diameter distance of $7.558 \pm 0.073$ (stat.) Mpc, within $0.13\sigma$ of the published maser distance.
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Cosmology and Nongalactic Astrophysics

The galaxy-electron cross-spectrum with ACT, SPT-3G and DESILS LRGs

Selim C. Hotinli

The galaxy–electron cross-power spectrum $P_{ge}(k)$ measures the small-scale distribution of gas around galaxies, the quantity reshaped by feedback. We measure $P_{ge}$ from the kinetic Sunyaev–Zel'dovich (kSZ) signal of the photometric DESI Legacy Imaging Surveys luminous red galaxies, cross-correlating a velocity-weighted galaxy momentum template with the CMB temperature from ACT DR6 and, for the first time, SPT-3G. The absolute normalization of the cross-spectrum is fixed by a surrogate-field Monte Carlo that propagates the survey mask, lightcone evolution, and photometric-redshift weights, converting the measured pseudo-spectrum into $P_{ge}(k)$ in physical units. We detect $P_{ge}$ at $11.7\sigma$ with ACT and $8.4\sigma$ with SPT-3G, and at $12.3\sigma$ combining SPT-3G with the ACT northern cap, which it does not overlap. The two surveys have independent optics, beams, filtering and noise and share about two thirds of the SPT-3G galaxies; their amplitudes agree channel by channel, the largest difference being $0.7\sigma$. All $26$ null tests on the adopted night maps are consistent with zero signal, among them the six ACT frequency differences, the three SPT-3G frequency differences, and the four ACT cap differences of the main selection. Turning the amplitude into a gas fraction requires the host halo masses of the sample, which the cross-spectrum does not itself measure; taking them from its measured number density and from a published CMB-lensing calibration of the same galaxies, the gas within the virial radius is $25$–$33\%$ of the cosmic baryon budget of the halo.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Massively parallel transdimensional sampling with data assimilation: an application to LISA galactic binaries

Gabriele Demasi and Walter Del Pozzo

Transdimensional Bayesian inference is becoming a key ingredient in gravitational-wave astronomy. In many relevant applications, the number of components needed to describe the data is not known a priori and must be inferred jointly with their parameters. We present a transdimensional Sequential Monte Carlo (SMC) framework designed to exploit massive parallelism. The method evolves a population of particles through a sequence of tempered distributions and uses the No-U-Turn Sampler for the exploration of fixed-dimensional parameter space while reversible-jump birth and death moves allow the number of components to vary. The same SMC construction also enables posterior samples obtained from a shorter data segment to be updated as additional data become available, enhancing the overall efficiency of the analysis. We validate the approach on two proof-of-concept problems: the recovery of a sequence of Gaussian pulses and a simplified LISA Galactic-binary inference problem. In both cases, the method recovers the injected number of components and produces consistent posterior estimates. These results indicate that the proposed method is a promising avenue toward scalable and parallel Bayesian transdimensional inference for current and future gravitational-wave astronomy.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

WIMPs with Enhanced Annihilation from a Feebly Interacting Unstable Partner

Chance Hoskinson, Pearl Sandick and Barmak Shams Es Haghi

Weakly interacting massive particles (WIMPs) constitute one of the best-motivated dark matter (DM) candidates. In this study, we consider a simple extension of the WIMP paradigm in which WIMPs are coupled to a heavier particle that interacts only with them and can decay into WIMPs. In the early Universe, when WIMPs are in thermal equilibrium with the Standard Model (SM) bath, they serve as a portal to populate the heavy partner through inverse decays. Depending on the lifetime of the partner particle, its eventual decay into WIMPs can significantly alter the WIMP abundance. If the partner decays into WIMPs before their freeze-out from equilibrium, the standard thermal history remains unchanged. When the decay occurs after WIMP freeze-out, however, the injected non-thermal population of WIMPs can result in an overproduction of DM, therefore requiring a larger WIMP annihilation cross section relative to the standard scenario without the partner. For a given partner lifetime and WIMP annihilation cross section, freeze-out may be delayed due to re-annihilation or followed by a freeze-in phase. By solving the Boltzmann equations both semi-analytically and numerically, we explore these thermal histories and study the required enhancement in the WIMP annihilation cross section compared to the canonical value. This enhancement, which can reach up to three orders of magnitude, leads to stronger annihilation signals in the late Universe. As a result, current and upcoming indirect detection experiments are able to probe the lifetime of the partner particle. We briefly explore possible connections between our scenario and the baryon asymmetry of the Universe. As an example, we show that the Next-to-Minimal Supersymmetric Standard Model (NMSSM) can provide a realization of our scenario, with the possibility of accommodating light higgsino DM with the correct relic abundance.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Proper Time Shifts in Pulsar Timing Arrays

Vincent S. H. Lee

Pulsar timing arrays are a powerful tool for probing low-frequency gravitational phenomena and physics beyond the Standard Model. We establish a general, gauge-invariant framework for the timing residual by identifying the measurable quantity as the proper time interval between consecutive pulse arrivals at Earth. In linearized general relativity, we derive a general expression for this proper time shift and show that it decomposes into Doppler, Shapiro, and Einstein delay contributions whose sum is gauge invariant, similar to frameworks that have been developed for other gravitational-wave detectors such as laser and atom interferometers. We also provide a recipe for computing the resulting timing residual for any specified perturbation, and we illustrate the method with several physically well-motivated sources, recovering known results where they exist in the literature. This recipe can be directly applied to search for new physics from real pulsar timing data using existing numerical software.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.IM

The OpenGadget3 Code for Cosmological Simulations

Klaus Dolag, Geray S. Karademir, Luca Tornatore et al. (+28 more)

We present the public release of OpenGadget3 (OG3), a substantially extended and re-organised version of the widely used Gadget-2/3 family of cosmological simulation codes. Since G2 was made publicly available, the absence of continued official development led to the creation of numerous, mutually incompatible developer versions of G3 across the community. This made it effectively impossible to track bug fixes, reproduce published results, or consistently credit the many individual contributors. OG3 addresses this by consolidating these disparate developments into a single, documented, and continuously maintained code base, released under the GNU GPLv3 through a GitLab repository (with an accompanying wiki), regularly synchronised with the active developer branch, and supported by a dedicated continuous-integration (CI) pipeline. OG3 retains the core algorithmic backbone of its predecessors, a Barnes&Hut oct-tree combined with a Particle-Mesh method for gravity, and a choice of Smoothed Particle Hydrodynamics or Meshless-Finite-Mass solvers for gas dynamics, within a hybrid MPI/OpenMP parallelisation framework, extended with GPU offloading via OpenACC and OpenMP. The code integrates an extensive suite of sub-resolution and physical modules, including primordial chemistry, radiative cooling, star formation, stellar feedback and chemical enrichment, dust formation and evolution, black hole growth and AGN feedback, MHD, thermal conduction, physical viscosity, SIDM, and massive neutrinos. OG3 introduces new features improving robustness, reproducibility, and usability: a flexible mixed-precision framework spanning 16- to 128-bit representations; expert-level tagged parameters with restart-time change log; extensive consistency checks against invalid configurations; and FAIR-compliant reporting of all settings, parameters, and specific publications. (shortened and abridged)
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All authors Klaus Dolag, Geray S. Karademir, Luca Tornatore, Antonio Ragagnin, Milena Valentini, Ludwig M. Böss, Frederick Groth, Giuseppe Murante, Stefano Borgani, Volker Springel, Cenanda Arido, Javier Badía, Tiago Castro, Alice Damiano, Laura Di Federico, Moritz S. Fischer, Gian Luigi Granato, Nitya Hariharan, David Klemmer, Umberto Maio, Tirso Marin-Gilabert, Ilaria Marini, Yashraj Patil, Margarita Egelhofer, Cinthia Ragone-Figueroa, Luca Sala, Cecilia Scannapieco, Ludwig D. Schmidt, Ulrich P. Steinwandel, Giovanni Tedeschi-Prades, Marc Wiertel

Cosmology and Nongalactic Astrophysics

$B$-sure. Part II. Scattering transforms as robustness test for tensor-to-scalar ratio detection from CMB observations

Claudio Ranucci, Sébastien Pierre, Léo Vacher et al. (+7 more)

Galactic foregrounds represent a major contamination to the measurement of primordial $B$-modes from observations of the Cosmic Microwave Background polarisation. Even after the application of component separation algorithms, foreground residuals may potentially still bias the estimate of the tensor-to-scalar ratio $r$, causing a false detection. In this work, we present the methodology of a robustness test for the validation of an eventual detection of primordial $B$-modes, as obtained by a future, LiteBIRD-like satellite experiment. The goal of the test is to identify the foreground residuals contamination by looking for non-Gaussian properties in the CMB $B$-modes map, recovered through blind component separation algorithms. We adopt scattering transforms (ST) as our summary statistics sensitive to the non-Gaussian features of foreground residuals and to their correlation with foregrounds tracer maps. We characterise and validate the methodology on realistic sky simulations with different levels of foregrounds complexity. The proposed test is able to identify a bias on the tensor-to-scalar ratio of $\gtrsim 10^{-3}$ in $\sim 90\%$ of our simulations, with this bias value being of the same order of the accuracy targeted by LiteBIRD. Additionally, for our particular experimental configuration, the test is passed when the bias is lower than the sensitivity on the $r$ parameter, and no warning is raised. These results provide an important step forward in the development of statistical tools for validating future measurement of cosmological parameters, against foregrounds contamination.
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All authors Claudio Ranucci, Sébastien Pierre, Léo Vacher, Alessandro Carones, Nicoletta Krachmalnicoff, Erwan Allys, Jean-Marc Delouis, Paolo Campeti, Giuseppe Puglisi, Carlo Baccigalupi

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

Vanilla Scotogenic Model at the future Muon Collider

Niloy Mondal, Dipankar Pradhan, Abhik Sarkar et al. (+2 more)

The vanilla scotogenic model (VSM) featuring three right-handed neutrinos and an inert scalar doublet, offers a unified explanation of neutrino masses, dark matter (DM), and the baryon asymmetry of the Universe through leptogenesis. The typical mass scale of such a scenario lies in the vicinity of $\sim$ 10 TeV and above, whereas enhanced second-generation Yukawa couplings lower the leptogenesis scale to $\sim 1$ \TeV, allowing the model to be probed at the future muon colliders. Adhering to DM, neutrino mass, Leptogenesis, and flavour dependent constraints, the charged scalar is likely to be a long-lived particle (LLP). We analyse both the prompt and displaced vertex signatures of the model to find that, prompt mono-photon signals remain challenging, but LLP searches offer a promising avenue to probe such a framework, subject to the timing resolutions, and displaced-vertex reconstruction efficiency.
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All authors Niloy Mondal, Dipankar Pradhan, Abhik Sarkar, Biplob Bhattacherjee, Subhaditya Bhattacharya

Cosmology and Nongalactic Astrophysics

The Equivalence Principle in the Dark Sector in light of DESI

Andrea Clini, Pierre Zhang, Emanuele Castorina et al. (+1 more)

Recent measurements of the distribution of galaxies by the Dark Energy Spectroscopic Instrument (DESI) are in mild tension with a standard $\Lambda$-Cold Dark Matter cosmological model inferred from the anisotropies of the Cosmic Microwave Background (CMB) when extrapolated to low redshifts. Several solutions to explain this discrepancy in terms of new physics have been put forward, notably from new dynamics in a complex Dark Sector. Here we report on a resolution to this discrepancy that postulates that the inertial and gravitational masses of dark matter particles are not the same. Our best fit to CMB data combined either with Baryon Acoustic Oscillation (BAO) and Full Shape (FS) data from DESI DR1 (Data Release 1), or with BAO DR2 data alone, suggests the presence of a new long-range force in the Dark Sector with strength of $\beta \sim 0.5\% $ relative to gravity, at the $\sim 2.5\sigma$ level. A preliminary analysis combining FS DR1 and BAO DR2 data confirms the statistical power of DR2 and raises the evidence for dark forces to $\sim 3\sigma$, albeit ignoring the not yet available cross-correlation between the two datasets.
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All authors Andrea Clini, Pierre Zhang, Emanuele Castorina, Maria Archidiacono

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

Cosmological Constrained Axion-Portal Inelastic Dark Matter for the LZ Event

Haipeng An, Fei Gao, Jia Liu et al. (+2 more)

The recent high-recoil candidate event reported by LUX-ZEPLIN (LZ) motivates dark-matter scenarios with nonstandard kinematics and momentum-dependent interactions. We study a two-state inelastic dark-matter model in which $\chi_1$ and $\chi_2$ couple off-diagonally to an axion-like particle (ALP) that also couples to gluons and photons. Unlike treatments that assume only one dark-matter state is present today, we track the cosmological evolution of both states. The excited state $\chi_2$ is sufficiently long-lived to survive to the present, with its relic fraction determined by the dark-sector conversion process $\chi_2\chi_2\leftrightarrow\chi_1\chi_1$. We find that this fraction depends strongly on the Lorentz structure of the DM–ALP interaction: scalar transition couplings efficiently deplete $\chi_2$, favoring endothermic $\chi_1 N\to\chi_2 N$ scattering, whereas pseudoscalar transition couplings preserve $f_2\simeq1/2$, yielding recoil spectra dominated by exothermic $\chi_2 N\to\chi_1 N$ down-scattering. Benchmark spectra in all four scenarios can peak near the observed recoil energy of $250\,\mathrm{keV}$. Our results demonstrate that the dominant direction of inelastic scattering in direct detection can be dynamically selected by the early-Universe evolution of the dark sector. With additional data, annual modulation measurements could distinguish these scenarios. We further show that the ALP portal can be directly probed at colliders.
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All authors Haipeng An, Fei Gao, Jia Liu, Minghao Liu, Changlong Xu

Cosmology and Nongalactic Astrophysics

Running Hubble Constant with the Redshift as a Marker of Evolutionary Dark Energy

Nakia Carlevaro, Giovanni Montani and Maria Giovanna Dainotti

We discuss the interpretation of an observed running Hubble constant with the redshift, in terms of the possible underlying physical scenario. Assuming, like in the $\Lambda$CDM model, that the matter and dark energy components do not directly interact, we arrive at the conclusion that the physical content of the cosmological dynamics can always be represented with an evolutionary dark energy paradigm. We discuss both the case of the power-law running Hubble constant, and that of an optimized fitting model, both studied with the binned Pantheon Sample of the Type Ia Supernovae data. These two cases turn out to be associated with a phantom-like evolutionary dark energy.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.HE

Caught by its own light: Wimpzillas, the LHAASO knee and the diffuse $\gamma$-ray sky

D. Akl, A.J. Iovino, D. Kantzas et al. (+1 more)

We use the proton spectrum resolved by LHAASO across the knee to test superheavy dark matter in the nucleon channel at PeV energies. Both the hardening at $0.34$ PeV and the knee at $3.3$ PeV are reproduced by nucleons from a relic of mass $5\cdot 10^{7}$ GeV decaying in the Galactic halo, with the mass as the only shape parameter of the spectrum and the background index profiled under an independent prior on the proton slope below $0.1$ PeV. It works equally well in all three hadronic-interaction-model reconstructions. On the other hand, the photons of the same cascade rule out this interpretation by about two orders of magnitude against the photon fraction of the cosmic radiation, and by about one order of magnitude against the LHAASO diffuse Galactic emission.
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All authors D. Akl, A.J. Iovino, D. Kantzas, A. V. Macciò

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

A fast radio burst from a non-targeted low-frequency survey

Cristian Di Pietrantonio, Marcin Sokolowski, Clancy W. James et al. (+13 more)

Fast radio bursts (FRBs) are bright, millisecond-duration transient radio signals of extragalactic origin with unknown source and emission mechanisms. While several thousand FRBs have been discovered at frequencies above 400 MHz, detections at lower frequencies have been exceptionally rare. Contributing to their rarity are the magnified dispersive delay, in the tens of seconds, and signal scattering that make low-frequency searches with established techniques computationally prohibitive. In particular, the only confirmed detection below 300 MHz came from a Low-Frequency Array observing campaign targeted at FRB 20180916B, a source already known to emit at higher frequencies. Here we present the first non-targeted detection of an FRB below 300 MHz, achieved in a wide-field, imaging-based survey with the Murchison Widefield Array. The implied FRB rate is consistent with that observed at higher frequencies, demonstrating that non-targeted wide-field surveys can uncover an unbiased, large low-frequency FRB population. This result challenges models invoking severe scattering or absorption to explain previous non-detections, and strengthens the case of low-frequency observations as promising avenue to study the local environment of FRBs.
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All authors Cristian Di Pietrantonio, Marcin Sokolowski, Clancy W. James, N. D. Ramesh Bhat, Randall Wayth, Danny C. Price, Christopher Harris, Chia Min Tan, Christopher P. Lee, Bradley W. Meyers, Mahitha Ega, Samuel J. McSweeney, Christopher Schlipalius, Gregory Sleap, Steven E. Tremblay, Mengyao Xue

Cosmology and Nongalactic Astrophysics

The WEFT project: I. The emergence of turbulence in a cosmic filament

Théo Lebeau and Saleem Zaroubi

Much of the ordinary matter in the present-day Universe still escapes direct detection. These missing baryons are thought to reside in a warm-hot intergalactic medium (WHIM) threading the filaments of the cosmic web, whose turbulent and thermal state remains poorly constrained yet underpins any attempt to observe it. Beyond its observational stakes, how this turbulence emerges, as gravitational collapse converts ordered inflow into a disordered cascade, is a question of structure formation in its own right. We characterise the emergence of turbulence in the diffuse gas of a cosmic filament, from its assembly to the present day, in the first simulation of the Web Evolution in Filament Targeted zoom simulations (WEFT) project. The cosmological zoom-in technique is applied to a single filament, evolved from z=63 to z=0 with the moving-mesh code AREPO, reaching a median gas cell size of ~8 kpc. We trace the filament assembly, the thermodynamic state of its diffuse gas, the generation of vorticity at its accretion shocks, and the growth of turbulent motions, then quantify the intermittency of the cascade through high-order velocity structure functions and their relative scaling exponents from extended self-similarity. The filament assembles by the hierarchical merging of several proto-filaments rather than by laminar accretion. Vorticity is seeded baroclinically where the rotating strands meet their accretion shocks obliquely. The flow evolves from a supersonic, shock-dominated state, statistically close to the bifractal Burgers limit, into a developed, mildly supersonic, intermittent cascade whose longitudinal exponents lie closest to the sheet-like She-Lévêque model at z=0. Turbulence is thus an intrinsic, quantifiable property of the diffuse gas of filaments. This pathfinder run provides the turbulent input for forecasts of WHIM observability.
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Cosmology and Nongalactic Astrophysics · Cross-listed from nucl-th

Alpha-Core Breakup in the Strong Decay of \({}_{\Lambda\Lambda}^{6}\mathrm{He}\) to a Deeply Bound \(H\) Dibaryon

Mahboubeh Shahrbaf and Makoto Oka

We investigate the effect of $\alpha$-core breakup on the strong conversion of \({}^{6}_{\Lambda\Lambda}\mathrm{He}\) into a deeply bound \(H\) dibaryon. In addition to the coherent \(H+{}^{4}\mathrm{He}\) channel, we evaluate the open final states \(H+p+{}^{3}\mathrm{H}\), \(H+n+{}^{3}\mathrm{He}\), and \(H+d+d\) using a translationally invariant Gaussian cluster description, including spin-isospin recoupling and full nonrelativistic three-body phase-space integrations. The breakup widths are normalized to Gal's intact-\(\alpha\) result. At \(B_{\Lambda\Lambda}^{H}=176~\mathrm{MeV}\), corresponding to \(m_H\simeq2055~\mathrm{MeV}\), the summed breakup width exceeds the intact-\(\alpha\) width by a factor \(R_{\mathrm{br}}=2.49\times10^{3}\). The resulting inclusive width and lifetime are \(\Gamma_{\mathrm{inc}}=3.87\times10^{-4}~\mathrm{eV}\) and \(\tau_{\mathrm{inc}}=1.70\times10^{-12}~\mathrm{s}\), respectively, compared with \(\tau_{\alpha}=4.25\times10^{-9}~\mathrm{s}\) for the intact-\(\alpha\) channel alone. The mass-dependent calculation shows that the inclusive lifetime crosses the characteristic hypernuclear weak-decay timescale near \(m_H\simeq2020~\mathrm{MeV}\) and increases rapidly as the \(H\) mass decreases. In the representative dark-matter-motivated interval \(1865\leq m_H\leq1885~\mathrm{MeV}\), we obtain \(6.59\times10^{-4}\lesssim\tau_{\mathrm{inc}}\lesssim 6.80\times10^{-3}~\mathrm{s}\), far exceeding the weak-decay timescale. Thus, although core breakup can dominate the inclusive strong width near \(m_H\simeq2055~\mathrm{MeV}\), weakly decaying double-\(\Lambda\) hypernuclei remain compatible, within the present framework, with a deeply bound \(uuddss\) state in the mass range relevant to sexaquark dark matter.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

The UV-to-FIR environments of nearby Type Ia supernovae with the DustPedia Galaxy Catalogue – I. Local versus global host properties

Lisa Kelsey

The ongoing use of Type Ia Supernovae (SNe Ia) as standardisable candles relies on an additional correction for the relationship between their standardised brightnesses and host galaxy properties. Currently, this correction is built on host stellar mass, typically derived from optical-only SED fitting, which recent analyses suggest may not fully capture the underlying environmental properties. This relationship is stronger when considering the regions closest to the SNe, rather than the galaxies as a whole. I use a sample of SNe Ia in DustPedia galaxies and CIGALE SED fitting to compare the local environments of 90 nearby SNe Ia against the global properties of their hosts. The UV-to-FIR coverage of DustPedia enables improved dust constraints, and helps break the age-dust degeneracy that limits optical-only studies; to my knowledge this coverage has not been previously applied to the sub-galactic regions around SNe Ia. Stellar mass and dust mass are lower locally simply because the aperture encloses less of the galaxy; however, for colour, sSFR, and dust attenuation, local values differ from the host average by more than measurement uncertainty alone allows, with attenuation showing the strongest discrepancy ($p=6.3\times10^{-5}$). Only mass-weighted age is consistent locally and globally. Galaxy-integrated properties therefore do not capture the true conditions at the SN location. SN siblings (sharing a host galaxy) only emphasise this effect. Siblings sampling the same galaxy structure, such as two SNe in spiral arms, have consistent environments, whilst others diverge. Standardising on global properties may therefore mask the differences that drive the brightness-environment relationship.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Limits on the Inferred Hubble Constant Bias from a Local McVittie Gravitational Field

Daniele Gregoris

We examine the exact propagation of light in a McVittie spacetime to quantify the observational bias introduced on the inferred Hubble constant $H_0$ by a localized central mass embedded in an expanding asymptotically de Sitter background. By integrating the Sachs optical equations for radial null geodesics, we derive linearized analytical expressions for the areal and luminosity distances to first order in the dimensionless Hawking-Hayward coupling parameter $\mu = H_{\text{dS}} m_H$. We evaluate the magnitude of this local gravitational field effect across realistic astrophysical scales, ranging from supermassive black holes ($\text{Sgr A}^*$) to galaxy cluster halos. We show that while a McVittie central mass induces a coordinate-invariant path-focusing effect on incoming photons, the quantitative correction for local galactic parameters ($\mu \sim 10^{-16}$) is negligible ($\sim 10^{-15}\%$), proving that a localized galactic mass alone cannot resolve the $\sim 8\%$ Hubble tension. We establish strict upper bounds on the extent to which local spacetime inhomogeneity can bias low-redshift distance ladder measurements.
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Cosmology and Nongalactic Astrophysics

Cosmological information from field-level analysis in redshift space

Julia Stadler

The field-level analysis of galaxy clustering with a forward model based on the Effective Field Theory of Large Scale structure provides cosmological measurements at optimal statistical precision which are simultaneously robust with respect to theoretical uncertainties regarding galaxy formation. Yet, the quantitative gains of field-level analysis in the perturbative regime over the current state-of-the-art, set by the combination of power- and bispectrum, are not obvious, and they depend on analysis choices, the cosmological model, and the observed galaxy population. We therefore quantify the precision improvement from field-level analysis over power- and bispectrum from redshift-space snapshots that closely resemble the DESI LRG sample. Our mock data are created with the LEFTfield forward model, which we also use for the subsequent field-level analysis and for a Fisher forecast of the power- and bispectrum precision. We find significant improvements from the field-level analysis over the power- and bispectrum for a $\Lambda$CDM cosmology; in particular the primordial fluctuation amplitude can be measured twice as precisely. Precision gains at the field-level are even more pronounced for extended cosmologies with a more flexible dependence between power spectrum shape and structure growth; they reach up to a factor of three in the primordial amplitude and a factor of two in parameters that capture deviations from $\Lambda$CDM. Our results highlight the potential of field-level analysis for future discoveries. Realizing this potential will require substantial developments on the modeling of observations and observational systematics as well as on the numerical inference techniques.
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Cosmology and Nongalactic Astrophysics

Probing multi-state dark matter via optical absorption lines in DESI spectra

Anoma Ganguly and Shadab Alam

We search for dark matter through absorption lines imprinted on the spectra of background sources whose sightlines pass through foreground dark matter halos. Such a line is a generic feature of multi-state dark matter models that couple to photons through higher-order electromagnetic moments. We focus on the minimal case of a two-state system with a magnetic dipole transition, in which the ground state absorbs a photon and makes a transition to the excited state. For transition energy $\Delta E \sim O \,(\text{eV})$, the line falls in the optical band, within reach of spectroscopic surveys such as DESI. Stacking 145,087 spectra of DESI Early Data Release objects paired with foreground GAMA galaxy groups, we find a stacked optical depth consistent with zero and place $2\sigma$ upper limits on the magnetic dipole transition cross-section. The limits are strongest at $\Delta E \sim$ 3-5 eV for a few MeV dark matter mass in the parameter space that is inaccessible to both cosmological (BBN+CMB) and direct detection experiments. We forecast that the full DESI and the next-generation spectroscopic surveys will tighten these limits by more than an order of magnitude, establishing spectroscopic stacking as a competitive probe of electromagnetically interacting multi-state dark matter.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Bridging Between Statistical Mechanics and Black Hole Evolution: Theoretical Formalism

Suvodip Mukherjee

Black holes in the Universe span nearly ten orders of magnitude in mass over a large cosmic timescale, dating back to at least the Universe's early history, when it was only a few hundred million years old. The formation and evolution of these objects remain a mystery because no direct probe can trace each black hole across the full mass range and cosmic time. This work shows, for the first time, a statistical mechanical description of black hole evolution. I show that though each black hole and its evolution are governed by stochastic processes, one can make a macroscopic description of the distribution function of black holes in the Universe, and its evolution over the entire mass range and cosmic time can be expressed in terms of the Kramers-Moyal expansion. This bridging between statistical mechanics and black hole evolution in terms of the Kramers-Moyal expansion enables the discovery of the underlying physical processes that play a role in the evolution of black holes. In the future, the application of this technique to data accessible from different messengers, such as gravitational waves and electromagnetic waves, which probe black holes in the Universe, can lead to a data-driven understanding of the underlying physical processes by this statistical mechanics technique despite the ignorance of the underlying microscopic stochastic processes.
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Monday 14 September

Cosmology and Nongalactic Astrophysics

FOSSIL: A future mission for CMB spectral distortion measurements

N. Aghanim, B. Maffei, J. Aumont et al. (+96 more)

We present FOSSIL, a proposed space mission which is designed to deliver unprecedented absolute spectroscopic measurements of the sky intensity over a broad frequency range (50GHz to 2THz) to accurately measure chemical-potential mu-type, Compton y-type, and Compton relativistic y-type CMB spectral distortions. FOSSIL will reach monopole sensitivities representing a gain of roughly three orders of magnitude over COBE/FIRAS. These capabilities will allow us to constrain primordial density fluctuations on scales k~(10 to 10^4)Mpc^-1, test inflationary models, probe dark matter annihilation/decay/interactions, constrain primordial black hole seed scenarios, and pin down feedback models in galaxy evolution and structure formation by measuring the cosmic thermal energy content. Furthermore, its 130 spectral channels will enable legacy astrophysics, including precise characterisation of the Cosmic Infrared Background, line intensity mapping during cosmic noon, and detailed Galactic dust mapping.
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All authors N. Aghanim, B. Maffei, J. Aumont, A. Beelen, B. Borgo, E. Bozzo, J. Chluba, X. Coulon, S. Couturier, F. Cuttaia, B. Cyr, P. De Bernardis, C. De Jabrun, J.-J. Diaz-Garcia, D. Eckert, G. Fabbian, L. Ferrari, F. Finelli, T. Gascard, J. E. Gudmundsson, A. Kogut, G. Lagache, M. Loquet Le Gall, S. Martin, A. I. Silva Martins, A. Monfardini, C. O'Sullivan, L. Pagano, D. Paoletti, G. Pisano, M. Remazeilles, V. Reveret, J. A. Rubino-Martin, V. Sauvage, G. Savini, L. Spencer, A. Tartari, L. Terenzi, N. Trappe, D. Watts, B. Winter, E. Baker, E. S. Battistelli, R. Battye, J. L. Bernal, A. Besnard, F. R. Bouchet, M. Braglia, C. Burigana, M. Calvo, S. Caminade, M. Citran, D. Clements, W. Coulton, E. Courau, G. De Zotti, E. Di Valentino, H. Dole, G. Domenech, S. Evangelista, S. Farrens, M. Frailis, K. A. Glasscock, V. Hervier, E. Kovetz, H. Liu, T. Louis, F. Madec, A. S. Maniyar, C. J. A. P. Martins, S. Masi, L. Maurin, F. Moll, L. Morelli, S. K. Naess, A. Nicola, F. Pace, N. Ponthieu, V. Poulin, E. Prele, N. Sanchez, W. Qin, L. Rodriguez, D. Scott, F. Simon, J. Singal, T. Slatyer, E. M. Teixeira, L. Thiele, M. Tristram, T. Trombetti, L. Vacher, S. Vinzl, A. Zacchei, E. Allys, K. Aryan, J. M. Casas Gonzales, O. Lahav, C. Sidiropoulos

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

Right Energy, Wrong Profile: Why the 43 GeV Cluster Line Is Unlikely to Be Dark Matter

Stefano Profumo

A narrow gamma-ray line would be a distinctive signature of dark matter, but its interpretation depends as much on its spatial distribution as on its energy. We reanalyze the reported 43 GeV feature in Fermi-LAT observations of Virgo, Fornax, and Ophiuchus. The excess is reproduced in the same public data and survives event-type partitions, a test using data withheld from the original selection, and detector-coordinate permutation tests. Realistic hadronic and inverse-Compton emission is too broad to explain it. A spatial–spectral likelihood analysis restricted to Good Time Intervals and including diffuse backgrounds and catalogued sources finds a broad line-like component. Uniform surface brightness and substructure-enhanced annihilation are preferred, whereas smooth NFW annihilation and a central point source are unlikely explanations. An independent annular analysis agrees: the events associated with the excess extend through much of the virial region. Calibration over 20–70 GeV and five morphologies gives a conditional global significance of approximately $2.7\sigma$, peaking at 44.5 GeV for uniform brightness. This result is conditional on the preselected three-cluster sample. The broad morphology is the main obstacle to a dark-matter interpretation. Such an interpretation would require photons to be a leading annihilation channel, annihilation to remain efficient in cold subhalos, and subhalos to supply nearly all the cluster luminosity. Yet a boost consistent with $\Lambda$CDM drives the required two-photon cross section into the range most tightly constrained by Galactic-halo line limits. The most likely explanation is a chance fluctuation amplified by analysis and target-selection effects, possibly compounded by residual Galactic diffuse or unresolved-source mismodeling; if celestial, its morphology makes a simple dark-matter interpretation unlikely.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

Gravitational Wave Bias in IllustrisTNG300 from Machine-Learned Population-Synthesis Calibrated Merger Rates

Dorsa Sadat Hosseini, Taisiia Karasova, Nikshay Chugh et al. (+2 more)

The large scale clustering of gravitational wave (GW) sources offers an independent probe of cosmology and compact-binary astrophysics. Interpreting future GW clustering measurements requires understanding how merger rates depend on host-galaxy properties and environment. We develop a simulation-based framework to model the clustering of binary black hole (BBH) mergers and estimate the corresponding GW bias. We populate IllustrisTNG300 with GW sources using a machine-learning emulator trained on the GALAXYRATE data set, which provides population-synthesis calibrated merger rates linked to galaxy formation histories. This enables physically motivated mock GW catalogs with galaxy-specific BBH merger rates that depend on stellar mass, star formation rate, metallicity, and redshift. We compare this framework to a simpler phenomenological model in which the merger rate depends only on stellar mass. In both approaches, GW sources are more strongly biased than the overall galaxy population, reflecting the preference for BBH mergers to occur in more massive, more strongly clustered halos. The machine-learned model also produces stronger scale dependence in the GW bias than stellar-mass weighting alone, indicating that additional host properties affect GW clustering. We further find that metallicity correlates positively with both GW and galaxy bias. These results highlight the importance of physically motivated merger rate models for GW large scale structure analyses and provide a framework for interpreting future clustering measurements from experiments such as the Einstein Telescope and Cosmic Explorer.
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All authors Dorsa Sadat Hosseini, Taisiia Karasova, Nikshay Chugh, Alex Krolewski, Ghazal Geshnizjani

Cosmology and Nongalactic Astrophysics

Peering Beyond the Veil of Last Scattering: A View of the Universe with CMB Spectral Distortions

Bryce Cyr, Nabila Aghanim, Ethan Baker et al. (+37 more)

The frequency spectrum of the cosmic microwave background is the most precise blackbody ever measured in nature, with deviations constrained at the level of almost one part per million from the COBE satellite. Nevertheless, departures away from a perfect blackbody are present in standard $\Lambda$CDM cosmology, lurking just beneath the surface of our current observational bounds. These spectral distortions provide invaluable information on our thermal history in both the post- and pre-recombination epochs, allowing us to peer beyond last scattering and into the primordial Universe. Here, we present an overview of the underlying physics responsible for generating CMB spectral distortions at all epochs. As an illustration of this rich physics, we review a comprehensive set of mechanisms capable of generating distortions both within and beyond the standard $\Lambda$CDM paradigm. We also discuss the information that can be gleaned by going beyond the monopole (sky-averaged) spectrum and exploiting the spatial information present in anisotropic spectral distortions. To supplement our discussion of the diverse science of spectral distortions, we provide an overview of the upcoming and proposed experimental landscape. We highlight that the combination of the TMS, COSMO, and BISOU experiments will provide the first discovery of a monopole $y$-type distortion within the coming decade. From space, the proposed FOSSIL experiment is forecasted to improve upon the original COBE/FIRAS measurement by roughly three orders of magnitude in sensitivity, bringing with it the detection of the $\Lambda$CDM $\mu$-type distortion sourced by the dissipation of small scale acoustic modes in the pre-recombination plasma. With transformational measurements on the horizon, CMB spectral distortions offer a uniquely sensitive probe of the thermal history of the Universe at redshifts $z \lesssim 2 \times 10^6$.
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All authors Bryce Cyr, Nabila Aghanim, Ethan Baker, Elia Stefano Battistelli, Richard Battye, José Luis Bernal, Jens Chluba, Xavier Coulon, William Coulton, Paolo de Bernardis, Eleonora Di Valentino, Guillem Domènech, Sara Evangelista, Giulio Fabbian, Fabio Finelli, J. Colin Hill, Rishi Khatri, Alan Kogut, Guilaine Lagache, Hongwan Liu, Bruno Maffei, Fereshteh Majidi, Abhishek S. Maniyar, C. J. A. P. Martins, Silvia Masi, Jeff McMahon, Daniela Paoletti, Vivian Poulin, Wenzer Qin, Mathieu Remazeilles, José Alberto Rubiño-Martín, Alina Sabyr, Mayuri Sathyanarayana Rao, Carlos Sierra, Jack Singal, Tracy R. Slatyer, Elsa M. Teixeira, Leander Thiele, Léo Vacher, Duncan Watts

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

Population III Host Candidates at $z\sim2$: Strong He II $\lambda1640$ and Absent UV Metal Lines in HETDEX Ly$\alpha$ Emitters

Mahan Mirza Khanlari, Dustin Davis, Karl Gebhardt et al. (+15 more)

Population III (Pop III) stars are expected to produce extremely hard ionizing spectra, yet direct evidence for their signature–strong narrow He II $\lambda1640$ emission with weak or absent metal lines–remains elusive. Although Pop III formation peaks at $z\gtrsim10$, models predict that nearly pristine gas pockets can survive to later times, making intermediate-redshift searches a probe of metal mixing across cosmic time. We search 109,545 high-confidence Ly$\alpha$-emitting galaxies at $1.9<z<2.3$ in the Hobby–Eberly Telescope Dark Energy Experiment's database for systems with strong He II $\lambda1640$ and no detected UV metal lines, recovering eight candidates and a first-order, tentative comoving number density of $\sim30$ Gpc$^{-3}$. The eight-object stack yields a rest-frame He II equivalent width of $28.7\pm6.7$ Angstrom, He II/Ly$\alpha=0.354\pm0.094$, and a resolution-corrected He II FWHM of $449\pm105$ km s$^{-1}$. We find no significant N V, C IV, or O III] emission; using the He II width to set the scale, we derive $3\sigma$ upper limits of N V/He II $<0.167$, C IV/He II $<0.128$, and O III]/He II $<0.140$. This combination of strong He II, elevated He II/Ly$\alpha$, moderate line width, and weak metal lines is difficult to reproduce with metal-enriched stellar populations, AGN narrow-line regions, shocks, or classical Wolf–Rayet features. We interpret the sample as candidates for very metal-poor or Pop III-like ionizing sources at $z\sim2$. Definitive confirmation requires deeper rest-UV spectroscopy to measure He II and metal-line limits in individual objects, followed by rest-optical spectroscopy of H$\beta$, [O III] $\lambda4959,\lambda5007$, [O II] $\lambda3727$, and H$\alpha$ to constrain gas-phase metallicity, ionization conditions, and AGN activity.
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All authors Mahan Mirza Khanlari, Dustin Davis, Karl Gebhardt, Tiger Yu-Yang Hsiao, Julian B. Muñoz, Alessandra Venditti, Erin Mentuch Cooper, Robin Ciardullo, Olivia Curtis, Daniel J. Farrow, Steven L. Finkelstein, Caryl Gronwall, Gary J. Hill, Wolfram Kollatschny, Chenxu Liu, Shiro Mukae, Shun Saito, Donald P. Schneider