Cosmology and Nongalactic Astrophysics
Emulation of the Halo Mass Function with Neural Networks
Olive Ross and Nicholas Battaglia
The abundance of
galaxy clusters as a function of mass — the
halo mass function (HMF) — depends strongly on cosmological parameters. Large-scale simulations are computationally expensive, motivating emulators that interpolate simulation outputs. We present a neural network emulator that maps cosmological and astrophysical parameters,
halo mass, and
redshift directly to a cumulative count of
halos above the input mass, avoiding the information loss inherent to binning and to the functional or PCA-based data reduction used in prior emulators. Each emulator prediction is accompanied by a self-estimated error, expressed in units of Poisson shot noise, that the network learns to predict alongside the
halo count itself — giving every output a built-in confidence metric. We validate the emulator with leave-one-out tests on three simulation suites — the N-body MassiveNus suite and the hydrodynamical CAMELS IllustrisTNG and SIMBA suites — spanning a range of box sizes,
redshifts, sub-grid physics, and softwares. Of all the held-out predictions ($1.2\times 10^6$ in total), 88% have model bias at or below shot noise and 99.9% are within $3\times$ shot noise. The only significant high-error tail is in MassiveNus, where the predicted model bias flags 76% of predictions exceeding $3\times$ shot noise; the remaining number of high error predictions is comparable to the number expected from shot noise alone. This emulator is publicly available and can be trained on other simulation suites making it a flexible HMF tool that can be used for cosmological and astrophysical inference.
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Cosmology and Nongalactic Astrophysics
ROBIN-PIP: Robust Bayesian Field-Level Inference with Physics-Informed Priors
Ludvig Doeser, Simon Ding, Guilhem Lavaux et al. (+1 more)
Accurately extracting information from
galaxy surveys, particularly at non-linear scales, requires increasingly complex and flexible forward models of the observed
galaxy distribution. A key component is the
galaxy bias relation, which connects the underlying matter distribution to observed
galaxies and requires more expressive representations than those currently incorporated into
Bayesian field-level inference. Certain parameterized models for this mapping can be overparameterized, with individual parameters carrying no direct physical interpretation, making them challenging to constrain. Our objective is to guide the inference of flexible model parameters towards physically plausible regions of parameter space through physics-informed priors. These priors are derived from high-fidelity simulations, thereby enabling the indirect use of simulations that cannot be integrated directly into gradient-based field-level inference. To this end, we introduce the ROBIN-PIP (RObust
Bayesian INference with Physics-Informed Priors) framework. As a proof of concept, we jointly infer the
cosmic initial conditions and the parameters of a truncated power-law
galaxy bias model for a simulated universe. We integrate ROBIN-PIP into the
Bayesian Origin Reconstruction from
Galaxies algorithm and
benchmark against inference without the simulation-based prior. With the additional prior, posterior standard deviations of the bias model parameters are reduced by up to $20\%$ and autocorrelation lengths are reduced from $730$-$870$ to $440$-$550$, increasing the effective sample sizes. We find no bias in the recovered initial conditions, demonstrating that ROBIN-PIP guides inference towards physically consistent solutions without compromising the data likelihood and highlighting its potential to incorporate overparameterized models in field-level inference.
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All authors Ludvig Doeser, Simon Ding, Guilhem Lavaux, Jens Jasche
Cosmology and Nongalactic Astrophysics
Constraining Primordial Magnetic Fields with Weak Lensing
Anna D'Ambrosio and Matteo Viel
Introducing primordial
magnetic fields (PMFs) into the standard cosmological model, $\Lambda$CDM, has an impact on the matter power spectrum at the linear level, resulting in an increase of power on small scales. In this work, we use the enhanced spectrum as the initial condition for dark-matter-only N-body simulations and study its non-linear
evolution. From the resulting non-linear matter power spectrum, we calculate the convergence power spectrum of weak
lensing ($C_{\kappa}$) and show how the presence of PMFs causes an enhancement at high multipoles. We then construct an emulator for $C_{\kappa}$ that also includes intrinsic
alignment and baryon feedback. We perform MCMC analyses using mock data generated for different PMF models and for three values of the maximum multipole, $\ell_{\rm max}=5000$, $10000$, and $20000$. The PMFs models are characterized by the two parameters that define the power-law power spectrum of the
magnetic field $P_B(k)\propto B_{\rm 1Mpc}^2 k^{n_B}$, where $B_{\rm 1Mpc}$ is the amplitude at a scale of $1$ Mpc and $n_B$ is the power spectral index. For $\Lambda$CDM mocks, corresponding to $B_{\rm 1Mpc}=0$, we obtain approximate upper limits of $B_{\rm 1Mpc}<1.6$, $1.0$, and $0.8\,{\rm nG}$ at the $95\%$ confidence level for the three values of $\ell_{\rm max}$ respectively. For non-zero input
magnetic fields, the recovery of $B_{\rm 1Mpc}$ and $n_B$ depends strongly on the PMFs model and on the maximum multipole considered. Models with $n_B=-2.1$ are more easily constrained than models with $n_B=-2.7$, since they produce a stronger enhancement of the convergence power spectrum. We find no clear degeneracy between the PMFs parameters and the intrinsic
alignment or baryon feedback parameters, while $B_{\rm 1Mpc}$ and $n_B$ can be degenerate. We characterize this degeneracy through linear fits to selected $2$D posterior distributions.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.IM
Inferring radio beams from sparse sampling patterns: a case study with the Murchison Widefield Array
Michael J. Wilensky and Aman Chokshi
Accurate primary-beam models are essential for high-dynamic-range
radio experiments, particularly searches for the redshifted 21-cm signal from the Epoch of Reionisation, where beam errors can couple bright foreground emission into the faint cosmological measurement. Using reprocessed satellite observations we infer the 137-MHz, zenith-pointed power beams of Murchison Widefield Array receiving elements. We develop two complementary
Bayesian approaches for quantifying departures from nominal electromagnetic simulations: a physically motivated model of complex variations among individual dipoles and a hierarchical spline model for flexible direction-dependent structure. The measurements reveal shallower and displaced nulls together with coherent sidelobe deformations. The dipole model captures much of this broad structure, whereas the spline recovers additional localised features while remaining largely robust to isolated pass-shaped artefacts. Despite their sparse and distinct sampling patterns, four independent 20-day subsets, each containing approximately 20% of the full
dataset, recover consistent null and sidelobe morphology across the visible hemisphere. These results demonstrate that opportunistic satellite transmissions can support practical, repeatable beam reconstruction, while motivating future chromatic, phase-referenced measurements of the full Jones response.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
LIGHTS. Limitations of Far-Infrared Tracers for Galactic Cirrus Mitigation in the Era of Ultra-Deep Imaging
Ouldouz Kaboud, Ignacio Trujillo, Ignacio Ruiz Cejudo et al. (+18 more)
Current and forthcoming deep optical imaging surveys are reaching surface brightness levels fainter than 30 mag/arcsec$^2$, where Galactic cirrus emission becomes a significant contaminant. This poses a major challenge for the study of extremely low-surface-brightness extragalactic structures. We investigate the relationship between far-infrared emission, as traced by the Herschel 250 $\mu$m band, and optical surface brightness in the Sloan g- and r-bands. We find that, for Galactic cirrus with $\mu_g\gtrsim$~27 mag/arcsec$^2$, a linear relation is consistent with the data, assuming optically thin dust, with optical cirrus emission amounting to $\sim$0.1% of the far-infrared flux. Using Herschel far-infrared data to trace Galactic cirrus enables its identification over wide areas, but at the cost of significantly reducing spatial resolution. This limitation introduces source confusion and restricts the effective surface brightness depth that can be robustly probed in optical data. We show that, when cirrus emission is modeled using Herschel 250 $\mu$m data, the limiting surface brightness is $\mu_V\sim$~28 mag/arcsec$^2$, substantially shallower than the nominal depth of surveys such as LIGHTS or the 10-year coadd LSST ($\mu_V\sim$~30.5 mag/arcsec$^2$). These results highlight a fundamental limitation in the use of currently available far-infrared data for cirrus mitigation in ultra-deep optical imaging, and emphasize the need for higher-resolution cirrus tracers to fully exploit the depth of upcoming surveys.
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All authors Ouldouz Kaboud, Ignacio Trujillo, Ignacio Ruiz Cejudo, S. Zahra Hosseini-ShahiSavandi, Mireia Montes, Sergio Guerra Arencibia, Mauro D'Onofrio, Dennis Zaritsky, Javier Roman, Nushkia Chamba, Giulia Golini, Chen-Yu Chuang, Minh Ngoc Le, Carlos Marrero-de la Rosa, Zahra Sharbaf, Richard Donnerstein, Sepideh Eskandarlou, Raul Infante-Sainz, Garreth Martin, Samane Raji, Nafise Sedighi
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
QCD axion misalignment during reheating
Disha Bandyopadhyay, Debasish Borah and Nayan Das
We study the production of QCD
axion dark matter (DM) via
vacuum and kinetic misalignment mechanisms during an extended reheating period after the end of slow-roll inflation. With pre-inflationary Peccei-Quinn breaking and considering a monomial inflaton potential during reheating, we classify our study into three different perturbative reheating scenarios in which the inflaton decays into (i) a pair of Standard Model (SM)-like
bosons, (ii) a pair of SM-like
fermions, or (iii) exclusively into a pair of heavy right-handed
neutrinos, which eventually decays into the SM final states after dominating the energy density of the Universe for an intermediate epoch. For each of these reheating scenarios, we study the details of QCD
axion relic separately via
vacuum and kinetic misalignment mechanisms. For different combinations of reheating, monomial inflaton potential and misalignment mechanisms, we identify the parameter space consistent with the observed DM relic density while satisfying other cosmological and laboratory constraints. We also check the scope of probing the currently allowed parameter space at
axion-detection and gravitational wave (GW) experiments.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Primordial Black Hole and Gravitational Wave by Peaked Cosmic Perturbations from Axion Curvaton
Keisuke Harigaya, Lian-Tao Wang and Jiangyi Yi
We demonstrate that an
axion field can develop perturbations peaked at an intermediate wavenumber through its inflationary dynamics. We compute the resultant spectrum of gravitational waves (GWs) and primordial black holes (PBHs) generated through the curvaton mechanism. The GW spectrum exhibits a triangular shape, with UV and IR slopes determined by the
axion's inflationary
evolution and treatable as free parameters. In computing the PBH abundance, we properly account for the nonlinear relation between
curvature and density perturbations and the primordial non-Gaussianity generated by the curvaton. The PBHs can account for all of dark matter, accompanied by blue-tilted isocurvature perturbations at small scales. The IR slope of the GW spectrum is anti-correlated with the magnitude of the dark matter isocurvature perturbations, offering a multi-messenger test of the model.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
From the Old to the New Starobinsky Inflation
Shinji Hirano
Starobinsky's original model of inflation, driven by the trace anomaly of conformal fields, and its $R+R^2$ (scalaron) formulation are often treated separately. The original anomaly-driven
evolution connects an early de Sitter phase supported by the Euler anomaly to a scalaron regime, where the observable modes leave the horizon. Building on this known background connection, we compute the scalar and tensor spectra on the exact background and find that the anomaly corrections are controlled by $aN_*/(18b)$, where $a$ and $b$ are the Euler-anomaly and $R^2$ coefficients and $N_*$ the number of e-folds after the pivot exits the horizon; scalaron inflation is recovered as this parameter vanishes. The observed tilt at $N_*=60$ then requires only $b/a\simeq35$, rather than the $b/a\gtrsim10^9$ of early realizations. At this
benchmark the scalar spectrum is redder than in scalaron inflation at fixed $N_*$, and the tensor-to-scalar ratio is about 17% lower at fixed tilt, a quantitative signature of the anomaly. For minimal gravitational reheating, $N_*\simeq53$, the tilt remains within $1\sigma$ of the Planck value for $b/a\gtrsim35$. In the de Sitter analysis, a finite range of the Weyl coupling excludes an extra real
spin-two pole and keeps the causal response decaying. A companion paper gives the full analysis.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
Probing the Reionization History and Bubble Sizes with JWST Lyman-$\alpha$ Fraction Measurements
Aritra Kundu, Adam Lidz and Guochao Sun
Recent James Webb Space
Telescope (JWST) measurements quantify the fraction of ultraviolet-selected
galaxies showing detectable Lyman-alpha (Ly-$\alpha$) lines at $z \sim 6-14$. These Ly-$\alpha$ fractions are partly shaped by Ly-$\alpha$ scattering from neutral hydrogen in the surrounding intergalactic medium (IGM), and so the observed Ly-$\alpha$ fraction
evolution can inform our understanding of the reionization history and the size distribution of ionized bubbles during reionization. We compare the JWST measurements with Ly-$\alpha$ transmission calculations based on both the THESAN reionization simulations and a flexible semi-analytic model. In each case, we calibrate a sub-grid model for the intrinsic Ly-$\alpha$ emission lines emerging from the interstellar medium (ISM) and circumgalactic medium (CGM) of the host
galaxies using empirical estimates of the Ly-$\alpha$ equivalent width (EW) distributions at $z \sim 6$. We find that the reionization history and bubble sizes in THESAN yield good agreement with current JWST Ly-$\alpha$ fraction observations, with a reduced $\chi^2_\nu = 0.4-1.2$. Our semi-analytic models and THESAN Ly-$\alpha$ transmission calculations agree well, allowing us to explore a wide range of reionization models. We derive $1\sigma$ bounds on the average mass-weighted neutral fractions of: $\langle x_{\mathrm{HI}} \rangle$ = $0.38^{+0.14}_{-0.38}$ ($0.52^{+0.09}_{-0.21}$), $0.57^{+0.23}_{-0.57}$ ($0.68^{+0.12}_{-0.39}$), and $0.93^{+0.05}_{-0.17}$ ($0.89^{+0.11}_{-0.15}$) at $z \sim$ 7, 8, and 11, based on the Ly-$\alpha$ fraction measurements with EW $>25\,\mathring{\rm A}$ ($>10\,\mathring{\rm A}$).
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Interpreting the High-Recoil LUX-ZEPLIN Event with Bino-/Singlino-like and Higgsino Dark Matter
Subhojit Roy, Pedro Schwaller and Carlos E. M. Wagner
The LUX-ZEPLIN (LZ) experiment has recently reported a nuclear-recoil candidate at $E_R\simeq248$ keV. We study two supersymmetric interpretations based on distinct neutralino couplings to the $Z$
boson. In the elastic case, a bino- or singlino-like neutralino scatters through a diagonal axial $Z$ coupling set by the Higgsino asymmetry $X=|N_{13}|^2-|N_{14}|^2$ rather than by the total Higgsino fraction. Since the
spin-dependent blind spot does not coincide with the
spin-independent one,
Higgs-mediated scattering can be suppressed while retaining $X\sim10^{-2}$. In the MSSM this favors low $\tan\beta$, in tension with the observed
Higgs mass for a few-TeV squark spectrum, a tension relieved by the tree-level quartic of the NMSSM. An explicit NMSSM
benchmark with $m_\chi\simeq500$ GeV and $X\simeq0.007$, below current LZ limits, obtains its relic abundance from a singlet-like pseudoscalar resonance just above threshold, which also suppresses present-day annihilation. In the inelastic case, a pseudo-Dirac Higgsino scatters endothermically, with a splitting of a few hundred keV generated by gauginos at the PeV scale which can be lowered by opposite-sign bino-wino cancellation, or by weak singlino mixing; the minimal thermal realization is strongly constrained by solar-
neutrino searches. The two mechanisms predict distinct recoil spectra away from the candidate.
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Cosmology and Nongalactic Astrophysics
Is DESI Seeing Dynamical Dark Energy, or a Cosmic Glitch in Gravity?
Robin Y. Wen, Lukas Tobias Hergt, Niayesh Afshordi et al. (+1 more)
Combined baryon acoustic oscillation and
cosmic microwave background data have begun to mildly favor departures from $\Lambda\mathrm{CDM}$. This is usually framed as 2-parameter dynamical dark energy. However, a 1-parameter "
cosmic glitch in
gravity" model, whose cosmological gravitational coupling differs from Newton's constant as in Hořava
gravity, fits at least as well. $\textit{Planck}$+ACT+SPT and DESI~DR2 give $G_\mathrm{cosmo}/G_\mathrm{N}=0.9920\pm0.0025$, a $3.3\,\sigma$ preference for weaker cosmological
gravity, robust to adding CMB
lensing and
supernovae. Fitted to the CMB alone, the glitch predicts DESI distances; $w_0w_a$CDM does not.
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All authors Robin Y. Wen, Lukas Tobias Hergt, Niayesh Afshordi, Douglas Scott
Cosmology and Nongalactic Astrophysics
Improved Constraints on Cosmic Microwave Background Circular Polarization with CLASS
Thomas Essinger-Hileman, Caleigh Ryan, Yunyang Li et al. (+25 more)
We present improved constraints on circular polarization in the
cosmic microwave background (CMB) from the Cosmology Large Angular Scale Surveyor (CLASS) experiment using data at 90, 150, and 220 GHz to complement previous results based on 40 GHz data alone. We extend constraints on circular polarization from the atmosphere to all CLASS frequencies and compare with a model of the atmospheric circular polarization spectrum. The inclusion of data at all CLASS frequencies improves upper limits on circular polarization, Stokes $V$, in the CMB by a factor of $\sim 5$ at the largest angular scales ($10 < \ell < 30$) and extends the constraints to smaller angular scales, $\ell = 700$. In combination with Planck temperature data, we provide the first limits on the temperature-circular-polarization ($TV$) power spectrum to date. Both circular polarization ($VV$) and $TV$ power spectra are consistent with zero, and CLASS places upper limits of $5.4 \times 10^{-3}$ $\mu$K$_{\text{CMB}}^2$ on $VV$ at large angular scale ($10 < \ell < 30$) and $5.8 \times 10^{-1}$ $\mu$K$_{\text{CMB}}^2$ on $TV$ at 95% confidence at $30 < \ell < 50$.
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All authors Thomas Essinger-Hileman, Caleigh Ryan, Yunyang Li, Matthew A. Petroff, John W. Appel, Charles L. Bennett, Ricardo Bustos, Carol Yan Yan Chan, David T. Chuss, Joseph Cleary, Sumit Dahal, Rahul Datta, Jullianna Denes Couto, Kevin L. Denis, Joseph R. Eimer, Joseph E. Golec, Kyle R. Helson, Jeffrey Iuliano, Tobias A. Marriage, Jeffrey J. McMahon, Ivan Padilla, Carolina Morales Perez, Karwan Rostem, Rui Shi, Deniz A. N. Valle, Duncan J. Watts, Janet L. Weiland, Edward J. Wollack
Cosmology and Nongalactic Astrophysics
A machine learning-based method for populating dark matter halos in N-body simulations with substructure
Milad Noorikuhani and Jeremy Tinker
Dark matter N-body simulations that resolve
halo substructure (subhalos) with high accuracy can be used for generating reliable catalogs of central and satellite
galaxies via
galaxy-
halo connection models. However, such simulations are computationally expensive, especially when large numbers of realizations are required for statistical analyses such as robust estimations of covariance
matrices for (statistical) cosmological quantities. In this work, we present a fast method for populating dark matter
halos in a given simulation box with subhalos extracted from a high-resolution simulation box with the same cosmology but arbitrary initial conditions. For each
halo in a given test set, the method first predicts whether it hosts at least one subhalo above a given mass threshold using a classifier built on a decision tree regressor. Then, for each predicted host, the method finds another host
halo in a given high-resolution box, using a nearest neighbor search in the space of selected
halo properties, and appropriately maps subhalos from that
halo to the test one. By applying the method to different test sets, we make predictions for abundances, distributions and three-dimensional and projected (two-dimensional) two-point correlation functions of various subhalo populations and sub-populations. In most cases, the percent errors of our predictions are well below 5%. In general, the method can be used to populate
halos in low-resolution simulation boxes with subhalos from a high-resolution simulation and also to investigate which
halo properties are (more strongly) correlated with subhalo abundance and clustering in a given dark matter simulation.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
When Streams Curve Away: a Test of Dark Matter from Extragalactic Stellar Stream Populations
Nathaniel Starkman, Jacob Nibauer, Sarah Pearson et al. (+2 more)
The nature of dark matter sets the shape of galactic
halos: collisionless cold dark matter (CDM) predicts triaxial
halos, while scattering in self-interacting dark matter (SIDM) rounds them toward sphericity. We show that a large catalog of projected stellar stream tracks can statistically constrain
halo shapes, and therefore the particle nature of dark matter, without detailed modeling of any individual stream or gravitational potential. We develop a new
geometric diagnostic for stellar streams: if the
curvature of any segment along a stream points away from the host
galaxy's projected center of mass, then that stream falsifies broad classes of potentials, including spherical ones. We call such a segment convex. The diagnostic needs only a projected stream track and a host-center estimate, requiring no kinematics, distances, progenitor model, or fit to individual host potentials.
Halo triaxiality sets the rate at which streams show convex segments, making this rate an observable of the
halo-shape distribution and the underlying dark-matter model. We forecast that upcoming survey-scale stream morphology catalogs can discriminate between CDM and SIDM at up to $5\sigma$.
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All authors Nathaniel Starkman, Jacob Nibauer, Sarah Pearson, Sirui Wu, Lina Necib
Cosmology and Nongalactic Astrophysics
Raising the Optical Depth to Reionization with Dark Matter Decay
Yu-Ning Wang, Paulo Montero-Camacho, Ziwei Wang et al. (+2 more)
DESI DR2 baryon acoustic oscillation measurements have sharpened a discrepancy with
cosmic microwave background (CMB) inferences that can be recast as a preference for a reionization optical depth of $\tau_{\rm reio}\simeq 0.09$, well above the $\simeq 0.06$ inferred from large-scale CMB polarization measurements. Here we test whether electromagnetic energy injection from dark matter (DM) decaying through $\chi\rightarrow e^{+}e^{-}$ can provide this additional optical depth. Adopting a Gompertzian model for astrophysical reionization, which provides an asymmetric, simulation-calibrated description of
cosmic reionization, we derive $\tau_{\rm reio}$ self-consistently from the
evolution of the free-electron fraction, including the contribution from DM decay. We jointly constrain cosmological and reionization parameters and the DM decay rate using ACT+Planck CMB temperature and polarization anisotropies, CMB
lensing, BAO measurements, and
quasar damping-wing observations. For $m_\chi=1\,{\rm GeV}$, DM decay raises the marginalized optical depth from $\tau_{\rm reio}=0.064$ to $0.072$, but does not significantly improve the fit. The additional optical depth arises primarily from a broad ionization tail extending through the
cosmic dark ages, rather than from an earlier onset of astrophysical reionization. Across $m_\chi=2\,{\rm MeV}$–$7\,{\rm GeV}$, the central $68\%$ credible intervals remain below the $\tau_{\rm reio}\simeq 0.08$ level previously found sufficient to bring both the
neutrino-mass tension and the exclusion of $\Lambda$CDM below the $2\sigma$ level. The corresponding DM lifetime constraints are complementary to
cosmic-ray and gas-heating bounds and competitive with previous CMB limits. Decaying DM therefore shifts the inferred optical depth in the direction required to ease the CMB–BAO discrepancy, but the allowed increase remains insufficient to alleviate it substantially.
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All authors Yu-Ning Wang, Paulo Montero-Camacho, Ziwei Wang, Yin Li, Yue-Lin Sming Tsai
Cosmology and Nongalactic Astrophysics
The Cosmological Correlation Dimension Beyond the Linear Regime: Analytical Approximation and Parameter Sensitivity
Miguel Aparicio Resco and Florencia A. Teppa Pannia
The correlation dimension ($D_2$) provides a scale-dependent characterization of the transition towards homogeneity and a complementary perspective on the clustering of large-scale structure. In this work, we study its full dependence on scales and
redshift connecting $D_2$ directly to the matter power spectrum of a given cosmological model, and derive an approximate analytical relation based on an effective cut-off representation of the filtering kernel. We further perform two complementary local (derivative-based) and global (variance-based) sensitivity analyses within the $w_0w_a$CDM model. In general, nonlinear
evolution lowers $D_2$ relative to the linear prediction at small scales, with the effect becoming more pronounced at low
redshift. Our cut-off approximation, with $k_{\rm cut}=\alpha/r$ and $\alpha\simeq 2.39$, reproduces the exact $D_2$ to better than 1% for the representative cases considered. The sensitivity analysis identifies $\Omega_m$ and $A_s$ as the dominant parameters for the linear correlation dimension and its nonlinear-to-linear ratio, respectively, while $w_0$ and $w_a$ induce scale- and
redshift-dependent changes in the nonlinear contribution. These results provide a framework for characterizing the cosmological scale- and
redshift-dependent features of $D_2$ and its nonlinear correction.
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Cosmology and Nongalactic Astrophysics
An improved standardization framework for Type II-P supernovae using a hierarchical Bayesian approach
A. Holas, S. Taubenberger, C. Vogl et al. (+41 more)
We use Type II-P
supernovae (SNe II-P) observed as part of the Nearby
Supernova Factory (SNfactory) experiment as standardizable candles to develop an improved standardization framework. The data consist of accurately flux-calibrated, host-subtracted spectrophotometry of low-
redshift SNe II-P in the wavelength range $3200 < \lambda < 10000$ ${\unicode{xC5}}$. We develop an improved method to determine the expansion velocities of SNe II-P based on Gaussian Process regression. We extend the conventional standardized candle method (SCM) by an additional correction term containing the H$_\alpha$ absorption-to-emission ratio and a hierarchical
Bayesian framework. We find that the additional correction improves the quality of the standardization, particularly around $30$ to $40$ days after the explosion. We are able to reduce the scatter of the Hubble-flow SNe II-P from $0.28$ mag down to $0.18$ mag compared to previous work. As an example application of this methodology we measure $H_0$ using a pre-existing calibrator sample of SNe~II having Cepheid- or TRGB-based distance moduli. We find a value of $H_0 = 70.6^{+4.5}_{-4.3}$ km s$^{-1}$ Mpc$^{-1}$, including only statistical uncertainty, corresponding to a precision of $6.2$%. We find variations of $1.4$ km s$^{-1}$ Mpc$^{-1}$ between hierarchical model variations — well within our quoted statistical uncertainty. Without the additional correction term, we obtain $H_0 = 73.0^{+6.9}_{-6.1}$ km s$^{-1}$ Mpc$^{-1}$ ($8.9$% precision) highlighting the improved precision of our new methodology. We identify and discuss inconsistencies between the measured parent populations of the calibrator and Hubble-flow standardization characteristics — present in this and literature samples — that are not explained by a simple selection on magnitude and which will need to be improved upon as SN II-P samples grow.
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All authors A. Holas, S. Taubenberger, C. Vogl, D. Rubin, M. Vincenzi, W. Hillebrandt, G. Aldering, P. Antilogus, C. Aragon, S. Bailey, C. Baltay, S. Benitez-Herrera, S. Bongard, K. Boone, C. Buton, G. Csörnyei, Y. Copin, S. Dixon, M. Fink, D. Fouchez, E. Gangler, R. Gupta, B. Hayden, E. E. O. Ishida, A. G. Kim, M. Klauser, M. Kowalski, M. Kromer, D. K. Küsters, J. Nordin, R. Pain, E. Pecontal, R. Pereira, S. Perlmutter, K. A. Ponder, D. Rabinowitz, M. Rigault, K. Runge, M. Sasdelli, C. Saunders, G. Smadja, N. Suzuki, C. Tao, R. C. Thomas
Cosmology and Nongalactic Astrophysics
Effects of a central dark matter core on time-delay cosmography with galaxy clusters
Yuting Liu and Masamune Oguri
The central dark matter distribution probes the nature of dark matter and baryon physics, yet its impact on time-delay cosmography is not fully explored. We update previous analyses of the cluster-lensed
quasar SDSS J1004+4112 and the
supernova Refsdal in MACS J1149.5+2223 by replacing the main
halo density profile from an elliptical Navarro-Frenk-White (NFW) profile to a cored elliptical NFW profile and investigating the impact of the central dark matter core on the Hubble constant $H_0$. We jointly infer $H_0$ and the dimensionless core size parameter $\beta=r_{\rm c}/r_{\rm s}$, while the Brightest Cluster
Galaxy (BCG) is either tied to the scaling relation of cluster member
galaxies or modeled separately, with its mass left free or assigned a Gaussian prior from the stellar mass estimate for a Chabrier or Salpeter initial mass function (IMF). For SDSS J1004+4112, constraints on both $\beta$ and $H_0$ strongly depend on the treatment of the BCG. A large core is implied when no prior is added to the BCG stellar mass, while a reasonable assumption on the BCG mass prefers a nearly cuspy
halo with $\beta\sim 10^{-3}$. For MACS J1149.5+2223, a large core of $\beta\sim 0.5$ is obtained with no prior, while a modest core of $\beta=0.0410^{+0.0865}_{-0.0276}$ is preferred when the Salpeter IMF is assumed. The constraint on $H_0$ from MACS J1149.5+2223 is stable against the BCG treatment, supporting its robustness. For the Salpeter-prior case, we obtain $H_0=65.9^{+3.5}_{-3.4}\mathrm{~km~s^{-1}~Mpc^{-1}}$, and different BCG assumptions change the median $H_0$ by less than $1\sigma$. The core size constraints are translated into the self-interacting dark matter cross section, giving a 95% upper limit of $\sigma/m<0.035\,\mathrm{cm}^{2}\,\mathrm{g}^{-1}$ from SDSS J1004+4112 and the 68% range of $\sigma/m=0.071^{+0.15}_{-0.045}\,\mathrm{cm}^{2}\,\mathrm{g}^{-1}$ from MACS J1149.5+2223.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Enhancing Constraints on Ultralight Axion Dark Matter from Gravitational Capture
Pierce Giffin, Pankaj Munbodh and Elisa G. M. Ferreira
Ultralight
axions can be gravitationally captured by massive bodies such as the Sun, producing solar-bound gravitational atom states that amplify the local dark matter density through Bose-enhanced capture. For
axion masses in the range $10^{-14}\text{eV}\lesssim m_a \lesssim 10^{-13}\text{eV}$, this mechanism becomes exponentially efficient. We show that, for a representative decay constant $f_a\sim 3.5\times10^7$ GeV, the local
axion dark matter density at Earth can grow to more than ten times the standard Galactic value of $\rho_0 = 0.4 \text{ GeV/cm}^{3}$. Incorporating this overdensity, we derive updated limits on the
axion-
photon coupling from existing satellite and terrestrial measurements and present improved projections for upcoming experiments.
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Cosmology and Nongalactic Astrophysics
An LSST-DESC Precursor Project: Hyper Suprime-Cam Year 1 $3\times2$pt in Harmonic Space
D. Sanchez-Cid, J. Sanchez, I. Sevilla-Noarbe et al. (+19 more)
We present the first fully photometric joint analysis of weak gravitational
lensing and
galaxy clustering (3$\times$2pt) in harmonic space with LSST-DESC analysis pipelines applied to Hyper Suprime-Cam Year 1 (HSC Y1) data. The HSC Y1
dataset, with imaging depth and
galaxy number density similar to those expected for the first year of LSST observations, is an ideal testbed for validating DESC measurement and inference tools. We measure the full set of angular power spectra -
cosmic shear,
galaxy clustering, and
galaxy-
galaxy lensing - perform null tests, and correct for the impact of observing conditions on both the
galaxy density and shear fields via mode deprojection. We validate our likelihood pipeline by reproducing the official HSC Y1
cosmic shear cosmological constraints with the DESC inference code. Jointly analysing all three two-point functions, we constrain $\Lambda$CDM and $w$CDM cosmologies, reporting results for
cosmic shear, the combination of
galaxy clustering and
galaxy-
galaxy lensing (2$\times$2pt), and the full 3$\times$2pt. From the joint 3$\times$2pt $\Lambda$CDM analysis we find $\Omega_m = 0.249^{+0.061}_{-0.051}$, $\sigma_8 = 0.904^{+0.098}_{-0.091}$, and $S_8 \equiv \sigma_8\sqrt{\Omega_m/0.3} = 0.821^{+0.018}_{-0.021}$. This analysis validates the complete DESC 3x2pt infrastructure on survey data, providing the foundation for the forthcoming LSST Year 1 cosmological analysis.
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All authors D. Sanchez-Cid, J. Sanchez, I. Sevilla-Noarbe, D. Alonso, F. Andrade-Oliveira, H. Awan, C. Chang, J. Ellison, C. García-García, M. Ishak, E. Longley-Phillips, R. Mandelbaum, A. Nicola, E. Pedersen, J. Prat, E. Rykoff, E. Sanchez, N. Šarčević, M. Soares-Santos, M. Yamamoto, J. Zuntz, the LSST Dark Energy Science Collaboration
Cosmology and Nongalactic Astrophysics
Exploring the Primordial Power Spectrum with Dark-Age 21 cm fluctuations
Fumiya Okamatsu, Tomo Takahashi and Shuichiro Yokoyama
We investigate the potential of future observations of the Dark Ages 21 cm power spectrum to probe the scale dependence of the primordial power spectrum and distinguish between inflationary models. We find that the Dark Ages 21 cm power spectrum can serve as a powerful probe of inflationary physics on scales beyond the reach of current CMB observations. While models predicting nearly identical running spectral indices may remain difficult to distinguish even with future 21 cm observations, models with unconventional scale dependence can be stringently tested. We further show that combining 21 cm observations with CMB data can significantly improve the constraints, even for a moderate observational configuration. We examine the impact of the choice of pivot scale on the resulting constraints.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
The impact of primordial magnetic fields on the formation of galaxies
Yao-Yu Li, Shihong Liao, Yue-Lin Sming Tsai et al. (+1 more)
Primordial
magnetic fields (PMFs), potentially generated during
cosmic inflation or early-universe phase transitions, can modify
cosmic structure formation by enhancing the post-recombination matter power spectrum. In this work, we investigate the impact of PMFs on
galaxy formation using a suite of high-resolution cosmological hydrodynamical simulations evolved to $z=0$. Our simulations are initialized with PMF-induced enhancements to the matter power spectrum and include more comprehensive baryonic subgrid models than previous work, incorporating both stellar and AGN feedback. We find that PMFs systematically accelerate early structure formation, producing more abundant
halos and
galaxies, higher baryon fractions, enhanced
star formation rates, and rapid growth of supermassive black holes at high
redshifts ($z \sim 10$). However, the resulting enhanced stellar and AGN feedback efficiently processes and expels gas, reducing the late-time differences between PMF and standard $\Lambda$CDM models. The PMF signatures are therefore strongest at high
redshift and gradually weaken toward low
redshift as nonlinear
evolution and baryonic feedback dominate over the initial PMF-induced enhancements. The impact of PMFs depends strongly on the characteristic peak scale, $k_{\rm peak}$, of the initial power enhancement, with models yielding similar non-linear
evolution if they share a similar $k_{\rm peak}$, even when other PMF parameters differ. Our results highlight the critical role of comprehensive baryonic physics in accurately quantifying PMF signatures.
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All authors Yao-Yu Li, Shihong Liao, Yue-Lin Sming Tsai, Yi-Zhong Fan
Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.HE
Electromagnetic Counterparts of Stellar-mass Binary Black Hole Mergers in AGN Accretion Disks: Theoretical Models and Observational Status
Lei He, Liang-Gui Zhu, Ken Chen et al. (+4 more)
The discovery of the binary
neutron star merger GW170817 and its electromagnetic counterparts marked the beginning of the era of multimessenger gravitational-wave astronomy. In contrast, binary black hole (BBH) mergers, which constitute the majority of gravitational-wave sources detected to date, are generally expected to be electromagnetically dark. However, if BBH mergers occur within the dense gaseous environments of active galactic
nucleus (AGN)
accretion disks, interactions between the merging black holes and surrounding gas may produce electromagnetic emission across multiple wavelengths. AGN disks may therefore provide a natural multimessenger laboratory for studying BBH mergers and their astrophysical environments. A key question is whether such a scenario is supported by current observations and whether the associated electromagnetic signatures are sufficiently distinctive and detectable. In this review, we summarize the current theoretical and observational status of BBH mergers in AGN
accretion disks, focusing on the evidence for their occurrence, the physical mechanisms and expected signatures of electromagnetic emission, and searches for candidate counterparts. We also discuss the major challenges in identifying and confirming these associations and the prospects for future multimessenger observations with current and forthcoming multiwavelength facilities.
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All authors Lei He, Liang-Gui Zhu, Ken Chen, Zi-Gao Dai, Ye-Fei Yuan, Jian-Min Wang, Wen Zhao