Many astrophysical systems of interest to numerical relativity—such as rapidly rotating stars, black hole accretion disks, and core-collapse supernovae—exhibit near symmetries. These systems generally consist of a strongly gravitating central object surrounded by an accretion disk, debris, and ejecta. Simulations can efficiently exploit the near axisymmetry of these systems by reducing the number of points in the angular direction around the near-symmetry axis, enabling efficient simulations over seconds-long timescales with minimal computational expense. In this paper, we introduce groovy, a novel code capable of modeling astrophysical systems containing compact objects by solving the equations of general relativistic hydrodynamics (GRHD) in full general relativity using singular curvilinear (spherical-like and cylindrical-like) and Cartesian coordinates. We demonstrate the code’s robustness through a battery of challenging GRHD tests, ranging from flat, static spacetimes to curved, dynamical spacetimes. These tests further showcase the code’s capabilities in modeling systems with realistic, finite-temperature equations of state and neutrino cooling via a leakage scheme. groovy extensively leverages grhayl, an open-source, modular, and infrastructure-agnostic general relativistic magnetohydrodynamics library built from the highly robust algorithms of illinoisgrmhd. Long-term simulations of binary neutron star and black hole–neutron star postmerger remnants will benefit greatly from using a future charm++-parallelized version of groovy to study phenomena such as remnant stability, gamma-ray bursts, and nucleosynthesis.

We present a framework to propagate to null infinity gravitational waves computed at timelike world tubes in the interior of $3+1$ (Cauchy) numerical relativity simulations. In our method, numerical relativity data are used as the inner inflowing boundary of a perturbative time-domain Regge-Wheeler-Zerilli simulation in hyperboloidal coordinates that reaches null infinity. We showcase waveforms from $(3+1)\mathrm{D}$ simulations of gravitational collapse of rotating neutron stars, binary black hole mergers and scattering, and binary neutron star mergers and compare them to other extrapolation methods. Our perturbative hyperboloidal extraction provides a simple yet efficient procedure to compute gravitational waves with data quality comparable to the Cauchy-characteristic extraction for several practical applications. Nonlinear effects in the wave propagation are not captured by our method, but the present work is a stepping stone toward more sophisticated hyperboloidal schemes for gravitational-wave extraction.

We present updated constraints on modified gravity by including the integrated Sachs-Wolfe (ISW) effect from cosmic microwave background (CMB) lensing-CMB temperature cross-correlations, based on the latest Planck PR4 maps. Utilizing the effective field theory (EFT) of dark energy approach and adopting the $w_0{w}_a\mathrm{C}\mathrm{D}\mathrm{M}$ background cosmological model, we find that including the CMB ISW-lensing cross-correlations tightens constraints on the modified gravity parameters by approximately 20%, reducing the viable parameter space by 40–80%. We derive constraints from Planck CMB, Planck and Atacama Cosmology Telescope CMB lensing, Dark Energy Spectroscopic Instrument Data Release 1 (DR1) BAO, CMB ISW-lensing, and type Ia supernovae data. The constraints on the EFT parameters controlling the kinetic braiding and nonminimal coupling are consistent with general relativity (GR) at the 95% C.L. In particular, we obtain a bound on the kinetic braiding parameter, $c_B<1.2$, at the 95% C.L. In the $w_0–w_a$ parameter space, our results imply a crossing of the phantom divide, $w=-1$. The modified gravity model shows a mild preference over $\mathrm{\Lambda }\mathrm{CDM}$ at the $1.8\sigma$, $2.6\sigma$, and $3.2\sigma$ levels for the combinations with Pantheon+, Union3, and DESY5 supernova datasets. We find that using the latest hillipop+lollipop likelihoods alleviates the departure of modified gravity parameters from the GR values compared to results using Planck 2018 data. This paper underlines the importance of the ISW-lensing probe in constraining late-time modifications of gravity.

The abundance of galaxy clusters as a function of mass and redshift is a well-established and powerful cosmological probe. Cosmological analyses based on galaxy cluster number counts have traditionally relied on explicitly computed likelihoods, which are often challenging to develop with the required accuracy and expensive to evaluate. In this work, we implement an alternative approach based on simulation-based inference (SBI) methods that relies solely on synthetic galaxy cluster catalogs generated under a given model. These catalogs are much easier to produce than it is to develop and validate a likelihood. We validate this approach in the context of the galaxy cluster survey of the upcoming Simons Observatory for a setup in which we can also evaluate an exact explicit likelihood. We find that our SBI-based approach yields cosmological parameter posterior means that are within $0.2\sigma$ of those obtained with the explicit likelihood and with biases smaller than $0.1\sigma$. We also introduce and validate a procedure to assess the goodness of fit using only synthetic catalogs similar to those used for training. This demonstrates, for the first time, that a galaxy cluster number count cosmological analysis can be performed fully without resorting to a likelihood at any stage. Finally, we apply our SBI-based approach to the real Planck MMF3 cosmology sample, obtaining cosmological parameter constraints that are within $0.1\sigma$ of their likelihood-based counterparts. This constitutes the first SBI-based number count cosmological analysis of a real galaxy cluster catalog.

Galaxy clusters provide a unique probe of the late-time cosmic structure and serve as a powerful independent test of the $\mathrm{\Lambda }\mathrm{CDM}$ model. This work presents the first set of cosmological constraints derived with $\sim 16,000$ optically selected redMaPPer clusters across nearly $5000{\mathrm{deg}}^2$ using DES year 3 datasets. Our analysis leverages a consistent modeling framework for galaxy cluster cosmology and DES-Y3 joint analyses of galaxy clustering and weak lensing ($3\times 2\mathrm{pt}$), ensuring direct comparability with the DES-Y3 $3\times 2\mathrm{pt}$ analysis. We obtain constraints of $S_8=0.864\pm 0.035$ and ${\mathrm{\Omega }}_{\mathrm{m}}=0.265_{-0.031}^{+0.019}$ from the cluster-based data vector. We find that cluster constraints and $3\times 2\mathrm{pt}$ constraints are consistent under the $\mathrm{\Lambda }\mathrm{CDM}$ model with a posterior predictive distribution (PPD) value of 0.53. The consistency between clusters and $3\times 2\mathrm{pt}$ provides a stringent test of $\mathrm{\Lambda }\mathrm{CDM}$ across different mass and spatial scales. Jointly analyzing clusters with $3\times 2\mathrm{pt}$ further improves cosmological constraints, yielding $S_8=0.811_{-0.020}^{+0.022}$ and ${\mathrm{\Omega }}_{\mathrm{m}}=0.294_{-0.033}^{+0.022}$, a 24% improvement in the ${\mathrm{\Omega }}_{\mathrm{m}}-S_8$ figure of merit over $3\times 2\mathrm{pt}$ alone. Moreover, we find no significant deviation from the Planck CMB constraints with a probability to exceed (PTE) value of 0.6, significantly reducing previous $S_8$ tension claims. Finally, combining DES $3\times 2\mathrm{pt}$, DES clusters, and Planck CMB places an upper limit on the sum of neutrino masses of $\sum m_{\nu }<0.26\mathrm{eV}$ at 95% confidence under the $\mathrm{\Lambda }\mathrm{CDM}$ model. These results establish optically selected clusters as a key cosmological probe and pave the way for cluster-based analyses in upcoming stage-IV surveys such as LSST, Euclid, and Roman.

Detecting anisotropic screening of the cosmic microwave background (CMB) holds the promise of revealing the distribution of gas in the Universe, characterizing the complex processes of galaxy formation and feedback, and studying the epoch of reionization. Estimators for inhomogeneous screening, including some recently proposed small-scale (stacked) estimators, are quadratic or higher order in the CMB temperature or polarization fields and are therefore subject to contamination from CMB lensing. We review the origin of this lensing bias and show that, when stacking on unWISE galaxies, the expected lensing bias dominates the signal if left unmitigated. Hardening techniques that null the lensing bias have been proposed for standard quadratic estimators, whereas only approximate methods have been proposed for stacked estimators. We review these techniques and apply the former to stacked estimators, presenting several strategies (including the optimal strategy) to null lensing contamination when stacking on any large-scale structure tracer.

Recent analysis of the DESI Collaboration challenges the $\mathrm{\Lambda }$-cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) model, suggesting evidence for a dynamic dark energy. These results are obtained in the context of generic parametrizations of the dark energy equation of state (EoS), which better fit the data when they exhibit an unphysical phantom behavior in the past. In this paper, we briefly analyze how ambiguous this latter conclusion can be in light of the background degeneracy between EoS parametrizations and minimally coupled quintessence scenarios. We then investigate whether the current observational data can be accommodated with a non-phantom, thawing dark energy EoS, typical of a broad class of quintessence models. We show that the thawing behavior of this EoS performs comparably to the Chevallier-Polarski-Linder parametrization and is statistically competitive with $\mathrm{\Lambda }\mathrm{CDM}$ while predicting cosmic acceleration as a transient phenomenon. Such a dynamic behavior aligns with theoretical arguments from string theory and offers a way out of the trans-Planckian problem that challenges the ever-accelerated $\mathrm{\Lambda }\mathrm{CDM}$ paradigm.

The theory of cosmic-ray (CR) penetration into dense molecular clouds developed recently for relativistic particles by Chernyshov et al. (2024) is extended to nonrelativistic CRs. Interstellar CRs propagating into the clouds are able to resonantly excite magnetohydrodynamic waves in diffuse cloud envelopes. This leads to the self-modulation, such that particles are scattered off of the self-generated waves. In contrast to relativistic CRs, transport of lower-energy particles in the envelopes is generally heavily affected by ionization losses; furthermore, both CR protons and electrons contribute to wave excitation. We show that these effects have profound impact on the self-modulation, and can dramatically reduce CR spectra even for clouds with moderate column densities of a few times ${10}^{21}{\mathrm{cm}}^{-2}$.

We present a simulation-based inference framework to constrain the neutron star (NS) equation of state (EoS) from astrophysical observations of masses, radii, and tidal deformabilities, using neural posterior estimation with conditional normalizing flows. To ensure that the model conforms with reality, physics-informed constraints are embedded directly into the training loss. This enables efficient, likelihood-free inference of full posterior distributions for key thermodynamic quantities—including pressure, squared speed of sound, and the trace anomaly—conditioned on observational data. Our models are trained on synthetic datasets generated from two agnostic EoS priors: polytropic parameterizations and Gaussian process reconstructions. These datasets span various scenarios, including the presence or absence of tidal deformability information and observational noise. Across all settings, the method produces accurate and well-calibrated posteriors, with uncertainties reduced when tidal deformability constraints are included. Furthermore, we find that the behavior of normalized predictive dispersions is strongly correlated with the maximum central density inside NSs, suggesting that the model can indirectly infer this physically meaningful quantity. The approach generalizes well across EoS families and accurately reconstructs derivative quantities such as the polytropic index, demonstrating its robustness and potential for probing dense matter in NS cores.

Gravitational wave (GW) transient searches rely on signal-noise discriminators to distinguish astrophysical signals from noise artifacts. These discriminators are typically tuned toward expected signal morphologies, which may limit their effectiveness as detector sensitivity improves and more complex signals, such as from core collapse supernovae or compact binary mergers featuring precession, higher-order harmonics, or eccentricity, become detectable. In this work, we use a convolutional neural network-based approach to classify noise transients from astrophysical transients, aiming to enhance the sensitivity of existing searches. We evaluate our method on two matched filter based searches, PyCBC-IMBH and PyCBC-HM tuned for intermediate-mass black hole (IMBH) binary systems. Our approach improves the sensitive volume reach of these searches by approximately 30% at a false alarm rate of once per 100 years. Finally, we apply our method to the first four chunks of the first half of the third observation run and demonstrate a marked improvement in significance. In particular, we significantly improve the first IMBH binary gravitational wave event GW190521 with an inverse false alarm rate exceeding 42000 yr.

Hadronic cosmic particles (cosmic rays) and gamma rays are constantly absorbed in the Earth’s atmosphere and result in air showers of secondary particles. Cherenkov radiation from these atmospheric events is used to measure cosmic gamma rays with ground-based telescopes. We focus here on the dominant hadronic cosmic-ray-initiated background events in the atmosphere, which give rise to gamma-ray-like air showers for gamma-ray telescopes. It is shown that only a small subset of hadronic cosmic-ray interactions, those which produce a large energy neutral pion, are responsible for this background. We subsequently address how the predictions of this background vary depending on the hadronic interaction model adopted. The pseudorapidity range of the energetic pions, with respect to the shower axis produced in these background events, is shown to be large. We show that collider experiments, specifically LHCf and the Relavistic Heavy Ion Collider (RHICf), probe cosmic ray interactions precisely within this pseudorapidity range. Present and future measurements with these instruments are shown to be able to test the ability for current hadronic interaction models to accurately describe these background events.

The recent NICER observation of PSR J0614-3329, revealing the smallest reliably measured neutron star radius of $R=10.29_{-0.86}^{+1.01}\mathrm{km}$ at mass $M=1.44_{-0.07}^{+0.06}{M}_{\odot }$, provides an unprecedented constraint on the equation of state of dense matter. We investigate the implications of this measurement for the origin of nucleon mass within the parity doublet model framework, which naturally incorporates both chiral variant and chiral invariant mass components. We construct unified equations of state by employing the parity doublet model with isovector scalar meson $a_0(980)$ for hadronic matter up to twice nuclear saturation density, smoothly connected to a Nambu-Jona-Lasinio-type quark model at higher densities through a crossover transition. By systematically varying the chiral invariant mass $m_0$ and quark matter parameters, we determine which values simultaneously satisfy all current astrophysical constraints, including gravitational wave observations from GW170817, NICER measurements of several pulsars, and the existence of two-solar-mass neutron stars. The inclusion of PSR J0614-3329 dramatically refines the allowed range of the chiral invariant mass from the previous constraint of $580\mathrm{MeV}\lesssim m_0\lesssim 860\mathrm{MeV}$ to $800\mathrm{MeV}\lesssim m_0\lesssim 860\mathrm{MeV}$, raising the lower bound by approximately 220 MeV. This result indicates that the chiral invariant mass must constitute at least 85% of the nucleon mass, challenging the traditional picture of nucleon mass generation through spontaneous chiral symmetry breaking alone and highlighting the importance of gluon condensation and other nonchiral mechanisms.

Gravitational wave observations have significantly broadened our capacity to explore fundamental physics beyond the Standard Model, providing crucial insights into dark matter that are inaccessible through conventional methods. Here, we investigate the resonant interactions between binary black hole systems and solitons, self-gravitating configurations of ultralight bosonic dark matter, which induce metric perturbations and generate distinct oscillatory patterns in gravitational waves. Upcoming experiments such as the Laser Interferometer Space Antenna could detect the oscillatory patterns in gravitational waveforms, providing an evidence for solitons. Because the effect relies solely on gravity, it does not assume any coupling of the dark sector to Standard Model particles, highlighting the capability of future gravitational-wave surveys to probe dark matter.

We evaluate global asymmetry in the luminosities of neutrinos emitted from rapidly rotating protoneutron stars (PNSs). We build axisymmetric models of PNSs in mechanical equilibrium with rotation by adding prescribed angular momentum distributions by hand to nonrotational PNS models, which are extracted from a one-dimensional (spherically symmetric) PNS cooling calculation at different times: $t=2$, 6, 10, 20, and 30 s after a supernova explosion. We then conduct two-dimensional (spatially axisymmetric) neutrino transport calculations on top of them with the matter profiles (and the spacetime geometry) fixed. We find for the rapidly rotating models with $T/|W|\sim 5\times {10}^{-2}$ that the neutrino luminosity changes by $\sim 3\%$ depending on the observer position. We give detailed analyses of the neutrino hemispheres, as well as the neutrino luminosities that are defined observerwise. We also calculate the low-frequency ($\lesssim 1\mathrm{Hz}$) gravitational waves produced by the neutrinos radiated asymmetrically. We find that those gravitational waves, if emitted from the Galactic Center, can be detected by planned detectors such as B-DECIGO, DECIGO, and AILA. Finally, we look for crossings in the energy-integrated angular distributions in momentum space for the electron neutrino sector, a signature of the fast flavor conversion. We find them near the PNS surface in all models.

Gamma-ray bursts (GRBs) are the most powerful electromagnetic outbursts in the Universe and emit a vast amount of their energy in the form of gamma rays. Their duration is extremely short on cosmic timescales, but they show a wealth of time variability in their light curves. Properties of this variability may carry information about the processes the gamma rays emerge from, which are still poorly understood. This research investigates the redshift-corrected gamma-ray light curves of 159 long GRBs, observed with the Gamma-ray Burst Monitor on the Fermi Gamma-Ray Space Telescope between 2008 and 2023. We calculate the average power-density spectrum of different groups of GRBs that are distinguished based on fluence, peak rate, duration, redshift, and the different GRB phases. Almost all redshift-corrected spectra reveal a power-law behavior with high-frequency power-law indices distributed around $\sim -1.9\pm 0.2$. The precursor phase and redshift-corrected short bursts exhibit a shallower power law with index $\sim -1.30\pm 0.04$, potentially due to the limited statistics that these samples represent. Only in some cases is the high-frequency index still consistent with the $-5/3$ (Kolmogorov) slope, found by earlier studies and linked to the appearance of fully developed turbulence.

The construction of equilibrium models of accretion disks around compact objects has become a highly relevant topic in the recent times, thanks to the current understanding that indicates a direct relationship between these objects with the electromagnetic emission of supermassive compact objects residing at center of the galaxies M87 and Milky Way, both of which were recently observed by the Event Horizon Telescope Collaboration. As the physical properties of the compact sources are estimated using the results of computer simulations of the system comprising of the disk plus the compact object, adding new physical ingredients to the initial data of the simulation is pertinent to enhance our knowledge about these objects. In this work, we thus present equilibrium solutions of geometrically thick, non-self-gravitating, constant orbital specific angular momentum, neutral Weyssenhoff spin fluid accretion tori in the Kerr spacetime, building upon a previous work that was restricted to the Schwarzschild geometry. Our models are obtained under the usual assumptions of stationarity and axisymmetry in the fluid quantities, circularity of the flow and a polytropic equation of state. We study how the deviations from an ideal no-spin fluid depend on both the magnitude of the macroscopic spin of the fluid and on the spin parameter of the Kerr black hole, carefully encompassing both the corotating and the counterrotating cases. Our results demonstrate that the characteristic radii, the thickness and the radial extent of such a torus can change importantly in the presence of the macroscopic spin of the ideal fluid. We also find some limitations of our approach that constrain the amount of spin the fluid can have in the rotating Kerr background. Finally, we present a parameter space exploration that gives us additional constraints on the possible values of the fluid spin denoted by the parameter $s_0$.

The data analysis of space-based gravitational wave detectors like Taiji faces significant challenges from nonstationary noise, which compromises the efficacy of traditional frequency-domain analysis. This work proposes a unified framework based on short-time Fourier transform (STFT) to enhance parameter estimation of Galactic binary and characterization of instrumental noise under nonstationarity. Segmenting data into locally stationary intervals, we derive STFT-based models for signals and noises, and implement Bayesian inference via the extended Whittle likelihood. Validated through the analysis of verification Galactic binaries and instrumental noises, our STFT approach outperforms frequency-domain methods by reducing the uncertainty and bias of estimation, successfully recovering low signal-to-noise ratio signals missed by frequency-domain analysis, and mitigating the degeneracy among noise parameters. The framework’s robustness against noise drifts and computational efficiency highlight its potential for integration into future global analysis pipelines.

The analysis of pulsar timing array data has provided evidence for a gravitational wave background in the nanohertz band. This raises the question of what is the source of the signal, is it astrophysical or cosmological in origin? If the signal originates from a population of supermassive black hole binaries, as is generally assumed, we can expect both to see evidence for anisotropy and to be able to resolve signals from individual binaries as more data are collected. The anisotropy and resolvable systems are caused by a small number of loud signals that stand out from the crowd. Here we focus on the joint detection of individual signals and a stochastic background. While methods have previously been developed to perform such an analysis, they are currently held back by the cost of computing the joint likelihood function. Each individual source is described by $N=8+2N_p$ parameters, where $N_p$ are the number of pulsars in the array. With the latest combined datasets having over one hundred pulsars, the parameter space is very large, and consequently, it takes a large number of likelihood evaluations to explore these models. Here we present a new approach that extends the Fourier basis method, previously introduced to accelerate analyses for stochastic signals, to also include deterministic signals. Key elements of the method are that the likelihood evaluations are per pulsar, avoiding expensive operations on large matrices, and the templates for individual binaries can be computed analytically or using fast Fourier methods on a sparsely sampled grid of time samples. The net result is an analysis that scales better than quadratically with the size of the dataset, while the approach currently being used in most analyses scales quartically or worse with the number of data points. As datasets grow with more observations, this analysis will be orders of magnitude faster than previous approaches.

We present a measurement of the mean number of muons with energies larger than 500 GeV in near-vertical extensive air showers initiated by cosmic rays with primary energies between 2.5 and 100 PeV. The measurement is based on events detected in coincidence between the surface and in-ice detectors of the IceCube Neutrino Observatory. Air showers are recorded on the surface by IceTop, while a bundle of high-energy muons (TeV muons) from the shower can subsequently produce a tracklike event in the IceCube in-ice array. Results are obtained assuming the hadronic interaction models Sibyll 2.1, QGSJet-II.04, and EPOS-LHC. The measured number of TeV muons is found to be in agreement with predictions from air-shower simulations. The results have also been compared to a measurement of low-energy muons by IceTop, indicating an inconsistency between the predictions for low- and high-energy muons in simulations based on the EPOS-LHC model.