The neutrino research program in the coming decades will require improved precision. A major source of uncertainty is the interaction of neutrinos with nuclei that serve as targets for such experiments. Broadly speaking, this interaction often depends, e.g., for charge-current quasielastic scattering, on the combination of “nucleon physics,” expressed by form factors, and “nuclear physics,” expressed by a nuclear model. It is important to get a good handle on both. We present a fully analytic implementation of the correlated Fermi gas model for electron-nucleus and charge-current quasielastic neutrino-nucleus scattering. The implementation is used to compare separately form factors and nuclear model effects for both electron-carbon and neutrino-carbon scattering data.

Dark matter could be a baryonic composite of stronglyc upled constituents transforming under ${\mathrm{SU}(2)}_L$. We classify the ${\mathrm{SU}(2)}_L$ representations of baryons in a class of simple confining dark sectors and find that the lightest state can be a pure singlet or a singlet that mixes with other neutral components of ${\mathrm{SU}(2)}_L$ representations, which strongly suppresses the dark matter candidate’s interactions with the Standard Model. We focus on models with a confining $\mathrm{SU}(N_c)$ and heavy dark quarks constituting vectorlike $N_f$-plet of $\mathrm{SU}(2{)}_L$. For benchmark $N_c$ and $N_f$, we calculate baryon mass spectra, incorporating electroweak gauge boson exchange in the nonrelativistic quark model, and demonstrate that above TeV mass scales, dark matter is dominantly a singlet state. The combination of this singlet nature with the recently discovered $\mathcal{H}$-parity results in an inert state analogous to noble gases, hence we coin the term noble dark matter. Our results can be understood in the nonrelativistic effective theory that treats the dark baryons as elementary states, where we find singlets accompanying triplets, 5-plets, or more exotic representations. This generalization of WIMP-like theories is more difficult to find or rule out than dark matter models that include only a single ${\mathrm{SU}(2)}_L$ multiplet (such as a wino), motivating new searches in colliders and a reanalysis of direct and indirect detection prospects in astrophysical observations.

We report the first observation and measurement of antiproton annihilation at rest on argon track and shower multiplicities and particle identification conducted with the LArIAT experiment. Stopping antiprotons from the Fermilab Test Beam Facility’s charged particle test beam are identified using beamline instrumentation and LArIAT’s liquid argon time projection chamber (LArTPC). The charged particle multiplicity from the annihilation vertex is manually evaluated via hand scanning, yielding a mean of $3.2\pm 0.4$ tracks and a standard deviation of 1.3 tracks, consistent with a semiautomated reconstruction resulting in $2.8\pm 0.4$ tracks and a standard deviation of 1.2 tracks. Both methods are consistent with Monte Carlo simulations within statistical uncertainty. The shower multiplicities and particle identification for outgoing tracks are also consistent with geant4 model predictions. These results, obtained from a low-statistics sample, provide a foundation for higher-statistics studies in larger LArTPCs, which could refine modeling of intranuclear annihilation on argon and inform scenarios such as neutron-antineutron oscillations.

In this paper we explore independently for the first time three chemical potentials (baryon ${\mu }_B$, charged ${\mu }_Q$, and strange ${\mu }_S$) in the chiral mean field (CMF) model. We designed and implemented cmf++, a new version of the CMF model rewritten in c++ that is optimized, modular, and well documented. cmf++ has been integrated into the MUSES Calculation Engine as a free and open-source software module. The runtime improved in more than 4 orders of magnitude across all 3 chemical potentials, when compared to the legacy code. Here we focus on the zero temperature case and study stable, as well as metastable and unstable, vacuum, hadronic, and quark phases, showing how phase boundaries vary with the different chemical potentials. Due to the significant numerical improvements in cmf++, we can now for the first time sweep the entire ${\mu }_B$, ${\mu }_S$, ${\mu }_Q$ phase space, investigate metastable phases, and calculate high-order susceptibilities within the CMF framework. This allows us to find phases of matter that include a light hadronic phase, a strangeness-dominated hadronic phase, and a quark phase. The numerical improvements also allow us to identify the order of the transitions among these phases, finding a first-order chiral symmetry restoration phase transition among the hadronic phases (favored for negative ${\mu }_Q$ and/or ${\mu }_S$ for some coupling schemes), in addition to third-order phase transitions. In particular, we identify for the first time triple points in the CMF model, where both chiral symmetry restoration and deconfinement phase transitions meet in the chemical potential phase space. Such points could potentially be identified in low-energy heavy-ion collisions.

We present a comprehensive reappraisal of the in-medium properties of the rho meson using the inverse QCD sum rules (QCDSR) formalism, offering a novel, model-independent approach to studying hadronic modifications in nuclear matter. Unlike conventional QCDSR, which rely on a predefined $\mathrm{pole}+\mathrm{continuum}$ structure, the inverse method reconstructs the spectral function directly from the operator product expansion (OPE), eliminating assumptions about the spectral ansatz. To the best of our knowledge, this is the first application of the inverse QCDSR method to the rho meson in nuclear matter. Our analysis reveals a significant reduction in the rho meson mass, consistent with previous theoretical predictions, and highlights the crucial role of medium-induced modifications, including condensate suppression and factorization-breaking effects. Furthermore, we assess the sensitivity of our results to the factorization assumption and higher-dimensional condensates, demonstrating the necessity of refining nonperturbative contributions for an accurate description of in-medium hadron properties. Our findings establish the inverse QCDSR method as a robust alternative to conventional spectral analysis techniques, providing a systematically controlled framework for exploring strongly interacting matter under extreme conditions. These results offer important theoretical benchmarks for lattice QCD simulations and heavy-ion collision experiments, shedding light on the restoration of chiral symmetry and the evolution of hadronic matter in dense environments.

Axions are a well-motivated candidate for dark matter. The preeminent method to search for axion dark matter is known as the axion haloscope, which makes use of the conversion of axions to photons in a large magnetic field. Because of the weak coupling of axions to photons, however, the expected signal strength is exceptionally small. To increase signal strength, many haloscopes make use of resonant enhancement and high gain amplifiers, while also taking measures to keep receiver noise as low as possible such as the use of dilution refrigerators and ultra-low-noise electronics. In this paper, we derive the theoretical noise model based on the sources of noise found within a typical axion haloscope receiver chain, using the Axion Dark Matter eXperiment (ADMX) as a case study. We present examples of different noise calibration measurements at 1280 MHz taken during ADMX’s most recent data-taking run. These new results shed light on a previously unidentified interaction between the cavity and Josephson Parametric Amplifier as well as provide a better understanding of the systematic uncertainty on the system noise temperature used in the axion search analysis for this data-taking run. Finally, the consistency between the measurements and the detailed model provide suggestions for future improvements within ADMX and other axion haloscopes to reach a lower noise temperature.

In this paper, we propose a generalization to the holomorphic modular bootstrap approach featuring flavored modular differential equations arising from null states of the algebra. The approach can be applied to rational and the more general quasilisse chiral algebras that arise in the study of four-dimensional superconformal field theories. The transformation property of the flavored equations reveals hidden and universal effective action of the modular group and spectral flow on the null states. As shown in examples, the equations compute the full ordinary and nonordinary spectra both in the untwisted and the twisted sector.

The $\mathrm{Einstein}\text{−}\mathrm{Rosen}=\mathrm{Einstein}\text{−}\mathrm{Podolsky}\text{−}\mathrm{Rosen}$ ($\mathrm{ER}=\mathrm{EPR}$) conjecture states that quantum entanglement between boundary degrees of freedom leads to the emergence of bulk spacetime itself. Although this has been tested extensively in string theory for asymptotically anti–de Sitter spacetimes, its implications for an accelerating universe, such as our own, remain less explored. Assuming a cosmic version of $\mathrm{ER}=\mathrm{EPR}$ for de Sitter space, we explore computational complexity corresponding to long-range entanglement responsible for bulk states on spacelike hypersurfaces. Rather remarkably, we find that the complexity (per unit volume) of the Euclidean vacuum, as an entangled state over two boundary conformal field theory vacua, is finite both in the UV and the IR, which provides additional evidence for “cosmic $\mathrm{ER}=\mathrm{EPR}$.” Our result seems to be a universal feature of spacetimes with horizons and, moreover, hints at new features of the thermofield double state for studying thermalization of any quantum system.

We investigate the entropy dynamics of de Sitter spacetime during the inflationary phase. The cosmological horizon in de Sitter spacetime, which limits the causally accessible region for an observer, exhibits thermal properties similar to a black hole event horizon. According to holographic principles, the entropy within a causally connected region is bounded by its surface area. However, this entropy bound is violated during the eternal phase of inflation. To address these violations from a quantum information perspective, we adopt a stochastic approach to cosmic inflation. Specifically, we analyze the Shannon entropy of the inflaton field’s probability distribution, which mirrors the behavior of the entanglement entropy of a Hubble-sized region in stochastic inflation. Using the volume-weighted probability distribution for the inflaton field, we demonstrate a significant entropy behavior in de Sitter spacetime.

We analyze the second order perturbations of the Deser-Woodard II (DWII), Vardanyan-Akrami-Amendola-Silvestri (VAAS), and Amendola-Burzilla-Nersisyan (ABN) nonlocal gravity models in an attempt to extract their associated gravitational wave energy-momentum fluxes. In Minkowski spacetime, the gravitational spatial momentum density is supposed to scale at most as $1/r^2$, in the $r\to \infty$ limit, where $r$ is the observer-source spatial distance. The DWII model has a divergent flux because its momentum density goes as $1/r$; though this can be avoided when we set to zero the first derivative of its distortion function at the origin. Meanwhile, the ABN model also suffers from a divergent flux because its momentum density goes as $r^2$. The momentum density from the VAAS model was computed on a cosmological background expressed in a Fermi-Normal-Coordinate system, and was found to scale as $r$. For generic parameters, therefore, none of these three dark energy models appear to yield well-defined gravitational wave energies, as a result of their nonlocal gravitational self-interactions.

In recent papers on spacetimes with a signature-changing metric, Capozziello et al. [Avoiding singularities in Lorentzian-Euclidean black holes: The role of atemporality, Phys. Rev. D 109, 104060 (2024).] and Hasse and Rieger [Pseudo-timelike loops in signature changing semi-Riemannian manifolds with a transverse radical, arXiv:2409.02403.] introduced, respectively, the concept of a Lorentzian-Euclidean black hole and new elements for Lorentzian-Riemannian signature change. In both cases the transition in the signature happens on a hypersurface $\mathcal{H}$. The former is a signature-changing modification of the Schwarzschild spacetime satisfying the vacuum Einstein equations in a weak sense. Here $\mathcal{H}$ is the event horizon which serves as a boundary beyond which time becomes imaginary. We clarify an issue appearing in Capozziello et al. based on numerical computations which suggested that an observer in radial free fall would require an infinite amount of proper time to reach the event horizon. We demonstrate that the proper time needed to reach the horizon remains finite, consistently with the classical Schwarzschild solution, and suggesting that the model in Capozziello et al. should be revised. About the latter, we stress that $\mathcal{H}$ is naturally a spacelike hypersurface related to the future or past causal boundary of the Lorentzian sector. Moreover, a number of geometric interpretations appear, as the degeneracy of the metric $g$ corresponds to the collapse of the causal cones into a line, the degeneracy of the dual metric $g^{*}$ corresponds to collapsing into a hyperplane, and additional geometric structures on $\mathcal{H}$ (Galilean and dual Galilean) might be explored.

Recent millimeter-wavelength observations of the near-horizon regions of $\mathrm{M}{87}^{*}$ and Sgr ${\mathrm{A}}^{*}$ by the Event Horizon Telescope have significantly advanced our understanding of gravity and astrophysics under extreme conditions. A key goal for future observations, with improved angular resolution and sensitivity, is the detection of the photon ring in these black holes. For Kerr black holes, photon rings exhibit universal scaling relations in terms of purely geometric observables: the demagnification exponent, time delay, and rotation parameter. Our study employs a nonperturbative, parametrized spinning spacetime to investigate how these observables vary with deviations from the no-hair theorem and the observer’s inclination. Particular emphasis is placed on polar observers, which is highly relevant for $\mathrm{M}{87}^{*}$. Our findings reveal that these observables encode vital information about the strong-field spacetime structure, including the morphology of the ergosphere. By analyzing specific non-Kerr spacetimes, we demonstrate that potential measurements of these observables, including the shadow size, can directly constrain the spin and Kerr-deviation functions. For polar observers, time delay measurements offer an independent estimate of the shadow size, providing a complementary probe of the black hole’s geometry. These results highlight the potential of using photon rings for precision tests of general relativity and for constraining strong-field deviations from Kerr spacetime.

Surrogate models of numerical relativity simulations of merging black holes provide the most accurate tools for gravitational-wave data analysis. Neural network-based surrogates promise evaluation speedups, but their accuracy relies on (often obscure) tuning of settings such as the network architecture, hyperparameters, and the size of the training dataset. We propose a systematic optimization strategy that formalizes setting choices and motivates the amount of training data required. We apply this strategy on NRSur7dq4Remnant, an existing surrogate model for the properties of the remnant of generically precessing binary black hole mergers and construct a neural network version, which we label NRSur7dq4Remnant_NN. The systematic optimization strategy results in a new surrogate model with comparable accuracy and provides insights into the meaning and role of the various network settings and hyperparameters as well as the structure of the physical process. Moreover, NRSur7dq4Remnant_NN results in evaluation speedups of up to 8 times on a single CPU and a further improvement of 2000 times when evaluated in batches on a GPU. To determine the training-set size, we propose an iterative enrichment strategy that efficiently samples the parameter space using much smaller training sets than naive sampling. NRSur7dq4Remnant_NN requires $\mathcal{O}({10}^4)$ training data, so neural-network-based surrogates are ideal for speeding up models that support such large training datasets, but at the moment cannot directly be applied to numerical relativity catalogs that are $\mathcal{O}({10}^3)$ in size. The optimization strategy is available through the gwbonsai package.

Wavelike dark matter may feature quadratic couplings to ordinary matter. This carries profound consequences for the phenomenologies of such models. It changes the dark matter density around dense objects made from ordinary matter such as planets and stars, thereby changing the sensitivity of direct detection experiments on Earth as well as implying forces on other ordinary matter objects in the vicinity. In this paper we study the time dependence of the dark matter field around spherical objects of ordinary matter. This work indicates the timescale on which accelerating objects settle into a stationary state and delineates the applicability of stationary solutions for experimental dark matter tests. We also use this to understand (and effectively eliminate) the infinities in energies, forces, and pressures that appear when naively comparing the total energy around objects with different size but the same total number of ordinary matter particles.

The XENONnT experiment searches for weakly interacting massive particle (WIMP) dark matter scattering off a xenon nucleus. In particular, XENONnT uses a dual-phase time projection chamber with a 5.9-ton liquid xenon target, detecting both scintillation and ionization signals to reconstruct the energy, position, and type of recoil. A blind search for nuclear recoil WIMPs with an exposure of 1.1 ton-years (4.18 t fiducial mass) yielded no signal excess over background expectations, from which competitive exclusion limits were derived on WIMP-nucleon elastic scatter cross sections, for WIMP masses ranging from $6\mathrm{GeV}/c^2$ up to the $\mathrm{TeV}/c^2$ scale. This work details the modeling and statistical methods employed in this search. By means of calibration data, we model the detector response, which is then used to derive background and signal models. The construction and validation of these models is discussed, alongside additional purely data-driven backgrounds. We also describe the statistical inference framework, including the definition of the likelihood function and the construction of confidence intervals.

We present sacra-2d, a new message passing interface and openmp parallelized, fully general relativistic hydrodynamics code in dynamical spacetime under axial symmetry with the cartoon method using the finite-volume shock-capturing schemes for hydrodynamics. Specifically, we implemented the state-of-the-art Harten-Lax–Van Leer contact Riemann solver and found better accuracy than the standard total variation diminishing Lax-Friedrichs Riemann solver. The spacetime evolves under the Baumgarte-Shapiro-Shibata-Nakamura formalism with Z4c constraint propagation. We demonstrate the accuracy of the code with some benchmark tests and excellent agreement with other codes in the literature. A wide variety of test simulations, including the head-on collision of black holes, the migration and collapse of neutron stars, and the collapse of a rotating supermassive star to a massive black hole and a disk, is also performed to show the robustness of our new code.

Exploring the equation of state of dense matter is an essential part of interpreting the observable properties of neutron stars. We present here the first results for dense matter in the zero-temperature limit generated by the MUSES calculation engine, a composable workflow management system that orchestrates calculation and data processing stages comprising a collection of software modules designed within the MUSES framework. The modules presented in this work calculate equations of state using algorithms spanning three different theories/models: (1) crust density functional theory, valid starting at low densities, (2) chiral effective field theory, valid around saturation density, and (3) the chiral mean field model, valid beyond saturation density. Lepton contributions are added through the lepton module to each equation of state, ensuring charge neutrality and the possibility of $\beta$-equilibrium. Using the synthesis module, we match the three equations of state using different thermodynamic variables and different methods. We then couple the complete equation of state to a novel full-general-relativity solver (QLIMR) module that calculates neutron star properties. We find that the matching performed using different thermodynamic variables affects differently the range obtained for neutron star masses and radii (although never beyond a few percent difference). We also investigate the universality of equation of state-independent relations for our matched stars. Finally, for the first time, we use the flavor equilibration module to estimate bulk viscosity and flavor relaxation charge fraction and rates (at low temperature) for chiral effective field theory and the chiral mean field model.

In this paper, we extend the results obtained in a previous work and investigate the most interesting decay processes involving axions, photons, and the lightest pseudoscalar mesons in the more general case in which the quarks (and, therefore, the mesons) may be charged under the $U(1)$ Peccei-Quinn symmetry, making use of a chiral effective Lagrangian model with $N_f=3$ light quark flavors, which also includes the flavor-singlet pseudoscalar meson and implements the $U(1)$ axial anomaly of the fundamental theory. In particular, we compute the axion mass, the electromagnetic coupling of the axion to photons, and the amplitudes and widths of the decay processes $\eta /{\eta }^{\prime }\to \pi \pi a$.