We propose a matrix model realization of a three-dimensional quantum space. It has an onionlike structure composed of concentric fuzzy spheres of increasing radius. The angular part of the Laplace operator is inherited from that of the fuzzy sphere. The radial part is constructed using operators that relate matrices of various sizes using the matrix harmonic expansion. As an example of this approach, we produce a numerical simulation of a scalar quantum field theory, the classical heat transfer, study the quantum-mechanical hydrogen atom, and consider some analytical aspects of the scalar field theory on this space.

Entanglement degradation appears to be a generic prediction in relativistic quantum information whenever horizons restrict access to a region of spacetime. This property has been previously explored in connection with the Unruh effect, where a bipartite entangled system composed of an inertial observer (Alice) and a uniformly accelerated observer (Rob) was studied, with entanglement degradation caused by the relative acceleration—and with equivalent results for the case when Alice is freely falling into a black hole and Rob experiences a constant proper acceleration as a stationary near-horizon observer. In this work, we show that a similar degradation also occurs in the case of an entangled system composed of an inertial observer (Alice) and a “diamond observer” (Dave) with a finite lifetime. The condition of a finite lifetime is equivalent to the restriction of Dave’s access within a causal diamond. Specifically, if the system starts in a maximally entangled state, prepared from Alice’s perspective, entanglement degradation is enforced by the presence of the diamond’s causal horizons.

Machine learning and artificial neural networks (ANNs) have increasingly become integral to data analysis research in astrophysics due to the growing demand for fast calculations resulting from the abundance of observational data. Simultaneously, neutron stars and black holes have been extensively examined within modified theories of gravity since they enable the exploration of the strong field regime of gravity. In this study, we employ ANNs to develop a surrogate model for a numerical iterative method to solve the structure equations of neutron stars (NSs) within a specific 4D Einstein-Gauss-Bonnet gravity framework. We have trained highly accurate surrogate models, each corresponding to one of twenty realistic EoSs. The resulting ANN models predict the mass and radius of individual NS models between 10 and 100 times faster than the numerical solver. In the case of batch processing, we demonstrated that the speed up is several orders of magnitude higher. We have trained additional models where the radius is predicted for specific masses. Here, the speed up is considerably higher since the original numerical code that constructs the equilibrium models would have to do additional iterations to find a model with a specific mass. Our ANN models can be used to speed up Bayesian inference, where the mass and radius of equilibrium models in this theory of gravity are required.

We construct models of two exotic objects: (i) a wormhole whose throat is hidden by a stellar object like a neutron star; and (ii) a wormhole inside a black hole. We work within Einstein’s gravity coupled to two scalar fields with a specific choice of the scalar field Lagrangian. In general, the model contains ghosts, but they are eliminated using the constraints given by the Lagrange multiplier fields. The constraints are a generalization of the mimetic constraint, where nondynamical dark matter effectively appears. As a result, in our model, instead of the nondynamical dark matter, nondynamical exotic matter like a phantom effectively arises. For the mixed wormhole-plus-star system, we find the corresponding mass-radius relation and show that it is possible to get characteristics comparable to those of ordinary neutron stars. For the wormhole inside the black hole, we find an extremal limit where the radius of the throat coincides with the radius of the event horizon and demonstrate that the Hawking temperature vanishes in this limit.

In this paper, we study the observational appearance of the asymmetric thin-shell wormhole (ATW) in Horndeski theory by employing the ray-tracing method. We first calculate the effective potential and null geodesic of the ATW, and then we obtain the deflection angle of the photon in the ATW spacetime. Based on the impact parameter of the photon, the trajectory of the photon can be classified into three cases. Two typical emission models of the thin accretion disk are considered to analyze the observational appearance of the ATW. By comparing the observational appearances of the ATW and a black hole with the same mass parameter, we find additional features in the observational appearance of the ATW, such as the “lensing band” and “photon ring group.”

Recently, Bueno, Cano, and Hennigar [Regular black holes from pure gravity, arXiv:2403.04827.] proposed a generic approach for incorporating an infinite tower of higher-curvature corrections into the Einstein theory. In this study, we compute quasinormal modes for certain regular $D$-dimensional black holes resulting from this infinite series of higher-curvature corrections, specifically focusing on the $D$-dimensional extensions of the Bardeen and Hayward black holes. We demonstrate that while the fundamental mode is minimally affected by moderate coupling constants, the higher overtones exhibit significant sensitivity even to small coupling values, yielding unconventional modes characterized by vanishing real oscillation frequencies. When comparing the frequencies derived from the metric truncated at several orders of higher-curvature corrections with those resulting from the infinite series of terms, we observe a rapid convergence of the frequencies to their limit for the complete regular black hole. This validates the extensive research conducted on specific theories with a finite number of higher-curvature corrections, such as the Lovelock theory.

General relativity (GR) and unimodular gravity (UG) provide two equivalent descriptions of gravity that differ in the nature of the cosmological constant. While GR is based on the group of diffeomorphisms that permits the cosmological constant in the action, UG is based on the subgroup of volume-preserving diffeomorphisms together with Weyl transformations that forbid the presence of the cosmological constant. However, the cosmological constant reappears in UG as an integration constant so it arises as a global degree of freedom. Since gauge symmetries are simply redundancies in our description of physical systems, a natural question is whether there exists a “parent theory” with the full diffeomorphisms and Weyl transformations as gauge symmetries so that it reduces to GR and UG, respectively, by performing suitable (partial) gauge fixings. We will explore this question by introducing Stueckelberg fields in both GR and UG to complete the gauge symmetries in each theory to that of the would-be parent theory. Despite the dynamical equivalence of the two theories, we find that precisely the additional global degree of freedom provided by the cosmological constant in UG obstructs the construction of the parent theory.

The generalized quasi-Keplerian parametrization for compact binaries on eccentric bound orbits is established at second post-Newtonian (2PN) order in a class of massless scalar-tensor theories. This result is used to compute the orbit-averaged flux of energy and angular momentum at Newtonian order, which means relative 1PN order beyond the leading-order dipolar radiation of scalar-tensor theories. The secular evolution of the orbital elements is then computed at 1PN order. At leading order, the closed form “Peters and Mathews” relation between the semimajor axis $a$ and the eccentricity $e$ is found to be independent of any scalar-tensor parameter, and is given by $a\propto e^{4/3}/(1-e^2)$. Finally, the waveform is obtained at Newtonian order in the form of a spherical harmonic mode decomposition, extending to eccentric orbits the results obtained in L. Bernard et al. [Gravitational waves in scalar-tensor theory to one-and-a-half post-Newtonian order, J. Cosmol. Astropart. Phys. 08 (2022) 008.].

We study the dynamics of Abelian gauge fields invariant under transverse diffeomorphisms (TDiff) in cosmological contexts. We show that in the geometric optics approximation, very much as for Diff invariant theories, the corresponding massless gauge bosons propagate along null geodesics and particle number is conserved. In addition, the polarization vectors are orthogonal to the propagation direction and the physical (transverse projection) polarization is parallel transported along the geodesics. We also consider TDiff invariant Dirac spinors, study the coupling to the gauge fields, and analyze the conditions in order to avoid violations of Einstein’s equivalence principle. The contributions to the energy-momentum tensor of the gauge field are also analyzed. We find that, in general, the breaking of Diff invariance makes the electric and magnetic parts of the vector field to gravitate in a different way. In the sub-Hubble regime we recover the standard radiationlike behavior of the energy density; however, in the super-Hubble regime the behavior is totally different to the Diff case, thus opening up a wide range of possibilities for cosmological model building. In particular, possible effects on the evolution of large-scale primordial magnetic fields are discussed.

We perform a reanalysis of the BOSS CMASS DR12 galaxy dataset using a simulation-based emulator for the wavelet scattering transform (WST) coefficients. Moving beyond our previous works, which laid the foundation for the first galaxy clustering application of this estimator, we construct a neural net-based emulator for the cosmological dependence of the WST coefficients and the 2-point correlation function multipoles, trained from the state-of-the-art suite of abacussummit simulations combined with a flexible halo occupation distribution (HOD) galaxy model. In order to confirm the accuracy of our pipeline, we subject it to a series of thorough internal and external mock parameter recovery tests, before applying it to reanalyze the CMASS observations in the redshift range $0.46<z<0.57$. We find that a joint $\mathrm{WST}+2$-point correlation function likelihood analysis allows us to obtain marginalized $1\sigma$ errors on the $\mathrm{\Lambda }\mathrm{CDM}$ parameters that are tighter by a factor of 2.5–6, compared to the 2-point correlation function, and by a factor of 1.4–2.5 compared to the WST-only results. This corresponds to a competitive 0.9%, 2.3% and 1% level of determination for parameters ${\omega }_c$, ${\sigma }_8\&n_s$, respectively, and also to a 0.7% and 2.5% constraint on derived parameters h and $f(z){\sigma }_8(z)$, in agreement with the Planck 2018 results. Our results reaffirm the constraining power of the WST and highlight the exciting prospect of employing higher-order statistics in order to fully exploit the power of upcoming stage-IV spectroscopic observations.

The diffuse supernova neutrino background (DSNB)—a probe of the core-collapse mechanism and the cosmic star-formation history—has not been detected, but its discovery may be imminent. A significant obstacle for DSNB detection in Super-Kamiokande (Super-K) is detector backgrounds, especially due to atmospheric neutrinos (more precisely, these are foregrounds), which are not sufficiently understood. We perform the first detailed theoretical calculations of these foregrounds in the range 16–90 MeV in detected electron energy, taking into account several physical and detector effects, quantifying uncertainties, and comparing our predictions to the 15.9 live time years of pre-gadolinium data from Super-K stages I–IV. We show that our modeling reasonably reproduces this low-energy data as well as the usual high-energy atmospheric-neutrino data. To accelerate progress on detecting the DSNB, we outline key actions to be taken in future theoretical and experimental work. In a forthcoming paper, we use our modeling to detail how low-energy atmospheric-neutrino events register in Super-K and suggest new cuts to reduce their impact.

We investigate the impact of magnetic fields on the potential barrier between two interacting nuclei. We addressed this by solving the Boltzmann equation and Maxwell’s theory in the presence of a magnetic field, resulting in the determination of magnetized permittivity. Additionally, we derived the magnetized Debye potential, which combines the conventional Debye potential with an additional magnetic component. We then compared the Boltzmann approach with the Debye method. Both methods consistently demonstrate that magnetic fields increase permittivity. This enhanced permittivity leads to a reduction in the potential barrier, consequently increasing the reaction rate for nucleosynthesis. Furthermore, the dependence on temperature and electron density in each approach is consistent. Our findings suggest that magnetized plasmas from the hot big bang Universe to the solar interior have played a crucial role in nucleosynthesis.

We report correlations in underground seismic measurements with horizontal separations of several hundreds of meters to a few kilometers in the frequency range 0.01 to 40 Hz. These seismic correlations could threaten science goals of planned interferometric gravitational-wave detectors such as the Einstein Telescope as well as atom interferometers such as MIGA and ELGAR. We use seismic measurements from four different sites, i.e., the former Homestake mine (USA) as well as two candidate sites for the Einstein Telescope, Sos Enattos (IT), and Euregio Maas-Rhein (NL-BE-DE) and the site housing the MIGA detector, LSBB (FR). At all sites, we observe significant coherence for at least 50% of the time in the majority of the frequency region of interest. Based on the observed correlations in the seismic fields, we predict levels of correlated Newtonian noise from body waves. We project the effect of correlated Newtonian noise from body waves on the capabilities of the triangular design of the Einstein Telescope to observe an isotropic gravitational-wave background (GWB) and find that, even in case of the most quiet site, its sensitivity will be affected up to $\sim 20\mathrm{Hz}$. The resolvable amplitude of a GWB signal with a negatively sloped power-law behavior would be reduced by several orders of magnitude. However, the resolvability of a power-law signal with a slope of e.g., $\alpha =0$ ($\alpha =2/3$) would be more moderately affected by a factor $\sim 6–9$ ($\sim 3–4$) in case of a low-noise environment. Furthermore, we bolster confidence in our results by showing that transient noise features have a limited impact on the presented results.

We test the predictions of hadronic interaction models regarding the depth of maximum of air-shower profiles, $X_{\max }$, and ground-particle signals in water-Cherenkov detectors at 1000 m from the shower core, $S(1000)$, using the data from the fluorescence and surface detectors of the Pierre Auger Observatory. The test consists of fitting the measured two-dimensional ($S(1000)$, $X_{\max }$) distributions using templates for simulated air showers produced with hadronic interaction models epos-lhc, qgsjet-ii-04, sibyll 2.3d and leaving the scales of predicted $X_{\max }$ and the signals from hadronic component at ground as free-fit parameters. The method relies on the assumption that the mass composition remains the same at all zenith angles, while the longitudinal shower development and attenuation of ground signal depend on the mass composition in a correlated way. The analysis was applied to 2239 events detected by both the fluorescence and surface detectors of the Pierre Auger Observatory with energies between ${10}^{18.5}\mathrm{eV}$ to ${10}^{19.0}\mathrm{eV}$ and zenith angles below 60°. We found, that within the assumptions of the method, the best description of the data is achieved if the predictions of the hadronic interaction models are shifted to deeper $X_{\max }$ values and larger hadronic signals at all zenith angles. Given the magnitude of the shifts and the data sample size, the statistical significance of the improvement of data description using the modifications considered in the paper is larger than $5\sigma$ even for any linear combination of experimental systematic uncertainties.

We develop a quantum kinetic theory for photons in the presence of an axion background and in the collisioness limit. In deriving the classical regime of our quantum kinetic equations, we observe that they capture well-known features of axion electrodynamics. By projecting the Wigner function onto a polarization basis, relating the Wigner matrix function with the Stokes parameters, we establish the dispersion relations and transport equations for each polarization space component. Additionally, we investigate how the axion background affects the dispersion relations of photon collective modes within an electron-positron plasma at equilibrium temperature $T$. While the plasmon remains unaffected, we find that the axion background breaks the degeneracy of transverse collective modes at order $e{g}_{a\gamma }T(\partial a)$, where $e$ represents the electron charge, $g_{a\gamma }$ denotes the photon-axion coupling, and $\partial a$ represents the scale associated with variations in the axion field.

We determine the quark mass dependence—light and heavy—of the $D_{s0}^{*}(2317)$ and $D_{s1}(2460)$ properties, such as, mass, coupling to $D^{(*)}K$, scattering lengths and compositeness, from a global analysis of $D^{(*)}K$ energy levels from LQCD. In particular, we analyze the HSC energy levels for $DK$ scattering in $I=0$ for different boosts and two pion masses. The formalism is based in the local hidden-gauge interaction of Weinberg-Tomozawa type which respects both chiral and heavy quark spin symmetries, supplemented by a term that takes into account the $D^{(*)}K$ coupling to a bare $c\overline{s}$ component. The isospin violating decay of the $D_{s0}^{*}(2317)\to D_s^{+}{\pi }^0$ is also evaluated.

We study di-Higgs and tri-Higgs boson productions at a muon collider as functions of the modification of the muon Yukawa coupling resulting from new physics parametrized by the dimension-six mass operator. We show that the di-Higgs signal can be used to observe a deviation in the muon Yukawa coupling at the 10% level for $\sqrt{s}=10\mathrm{TeV}$ and at the 3.5% level for $\sqrt{s}=30\mathrm{TeV}$. The tri-Higgs signal improves the sensitivity dramatically with increasing $\sqrt{s}$, reaching 0.8% at $\sqrt{s}=30\mathrm{TeV}$. We also study all processes involving Goldstone bosons originating from the same operator, discuss possible model dependence resulting from other operators of dimension-six and higher, and identify ${\mu }^{+}{\mu }^{-}\to hh$, ${\mu }^{+}{\mu }^{-}\to hhh$, and ${\mu }^{+}{\mu }^{-}\to h{Z}_L{Z}_L$ as golden channels. We further extend the study to an effective field theory including two Higgs doublets with type-II couplings and show that di-Higgs and tri-Higgs signals involving heavy Higgs bosons can be enhanced in the alignment limit by a factor of $(\tan \beta {)}^4$ and $(\tan \beta {)}^6$, respectively, which results in the potential sensitivity to a modified muon Yukawa coupling at the ${10}^{-6}$ level already at a $\sqrt{s}=10\mathrm{TeV}$ muon collider. The results can easily be customized for other extensions of the Higgs sector.

We compute the one-loop quark-photon vertex and the quark magnetic moment in three different models with an infrared-modified gluon propagator, namely: the massive (Curci-Ferrari-like) model, the Gribov-Zwanziger model, and the refined Gribov-Zwanziger model. We show results for the $F_2$ form factor and analyze the role played by the mass parameters associated with the confined gluon in these models. Using the framework of the constituent quark model, we further construct the observable proton magnetic moment including the effects of quantum chromodynamics (QCD) interactions generated by the different confining models. Our results show that there is no qualitative observable difference stemming from the presence of complex-conjugated poles. On the other hand, quantitative differences between the various confining models can be sizable, so that observable constraints would in principle be possible, provided one has sufficient information about the constituent quark mass and the QCD running coupling.

We analyze theoretically the coupled-channel meson-baryon interaction with global flavor $\overline{c}cssn$ and $\overline{c}csss$, where mesons are pseudoscalars or vectors, and baryons have $J^P=1/2^{+}$ or $3/2^{+}$. The aim is to explore whether the nonlinear dynamics inherent in the unitarization process within coupled channels can dynamically generate double- and triple-strange pentaquark-type states ($P_{css}$ and $P_{csss}$, respectively), for which there is no experimental evidence to date. We evaluate the s-wave scattering matrix by implementing unitarity in coupled channels, using potential kernels obtained from t-channel vector meson exchange. The required $PPV$ and $VVV$ vertices are obtained from Lagrangians derived through appropriate extensions of the local hidden gauge symmetry approach to the charm sector, while capitalizing on the symmetry of the spin and flavor wave function to evaluate the $BBV$ vertex. We find four different poles in the double strange sector, some of them degenerate in spin. For the triple-strange channel, we find the meson-baryon interaction insufficient to generate a bound or resonance state through the unitary coupled-channel dynamics.