Monoenergetic $\gamma$-ray spectral lines are among the cleanest signatures of dark matter annihilation. We analyze 15 years of Fermi-LAT data, find no spectral lines, and place strong constraints on dark matter annihilation to monoenergetic $\gamma$-rays. Additionally, we produce the first double-line analysis of the coupled signals from $\gamma \gamma$ and $Z\gamma$ lines, which proves particularly powerful for dark matter masses above $\sim 150\mathrm{GeV}$. From our constraints on a double-line feature, we investigate and constrain some minimal models where the Galactic Center Excess can be fit by dark matter annihilation through the Higgs boson into Standard Model particles.

We generalize, imposing the field equations only at dominant order, the Isaacson formula for the gravitational wave (GW) energy-momentum tensor (EMT) to the class of Horndeski theories in which the tensor modes travel at the speed of light (reduced Horndeski theories) and scalar waves are present. We discuss important particular cases such as theories where scalar waves are also luminal and theories in which the transverse-traceless gauge can be achieved in an arbitrary open set. The vanishing of the trace of the gravitational wave energy-momentum tensor is obtained for theories in which all wave perturbations propagate at the speed of light. The trace is shown not to vanish trivially in other cases. We obtain, as a particular case of our general result, the GW EMTs, in a Brans-Dicke theory, both in the Einstein frame, recovering previous results in the literature, and in the Jordan frame, thereby showing the GW EMT is not conformally invariant. We further prove that there exists a subclass of reduced Horndeski theories where, in contrast to general relativity, the divergence of the GW EMT does not vanish even after the imposition of the full equations of motion, assuming an eikonal solution.

In this paper we explore properties of the spacetime of the monopole in nonlinear $\sigma$-models in the Eddington inspired Born-Infeld gravity. Particularly, we examine the radii of characteristic circular orbits of the test particles such as the circular null geodesics, marginally bound and stable circular orbits as a function of the spacetime parameters. Furthermore, we explore the dynamics of the massless scalar field. To enhance the precision of calculations, we employ multiple methods, including the WKB (Wentzel-Kramers-Brillouin) approximation, asymptotic iteration, and continued fractions methods. Our calculations demonstrate that the scalar field within the field of the monopole under examination remains stable against scalar perturbations. Notably, variations in the monopole parameter influence the longevity of the damping time of perturbations, with smaller damping rates prolonging their existence.

Theories of gravity with auxiliary fields are of particular interest since they are able to circumvent Lovelock’s theorem while avoiding the introduction of new degrees of freedom. This type of theories introduces derivatives of the stress-energy tensor in the modified Einstein equation. This peculiar structure of the field equations was shown to lead to spacetime singularities on the surface of stars. Here we focus on yet another problem afflicting gravity theories with auxiliary fields. We show that such theories can generically introduce parametrically large deviations to the Standard Model unless one severely constrains the parameters of the theory, preventing them to produce significant phenomenology at large scales. We first consider the specific case of Palatini $f(\mathcal{R})$ gravity, to clarify the results previously obtained in Ref. [1]. We show that the matter fields satisfy the Standard Model field equations which reduce to those predicted by general relativity in the local frame only at tree level, whereas at higher orders in perturbation theory they are affected by corrections that percolate from the gravity sector regardless of the specific $f(\mathcal{R})$ model considered. Finally, we show that this is a more general issue affecting theories with auxiliary fields connected to the same terms responsible for the appearance of surface singularities.

The Arnowitt-Deser-Misner (ADM) energy for asymptotically flat spacetimes or its generalizations to asymptotically nonflat spacetimes measure the energy content of a stationary spacetime, such as a single black hole. Such a stationary energy is given as a geometric invariant of the spatial hypersurface of the spacetime and is expressed as an integral on the boundary of the hypersurface. For nonstationary spacetimes, there is a refinement of the ADM energy, the so-called Dain’s invariant that measures the nonstationary part, the gravitational radiation component, of the total energy. Dain’s invariant uses the metric and the extrinsic curvature of the spatial hypersurface together with the so-called approximate Killing initial data and vanishes for stationary spacetimes. In our earlier work [E. Altas and B. Tekin, Nonstationary energy in general relativity, Phys. Rev. D 101, 024035 (2020)], we gave a reformulation of the nonstationary energy for vacuum spacetimes in the Hamiltonian form of general relativity written succinctly in the Fischer-Marsden form. That formulation is relevant for merging black holes or other compact sources. Here we extend this formulation to nonvacuum spacetimes with a perfect fluid source. This is expected to be relevant for spacetimes that have a compact star, say a neutron star colliding with a black hole or another nonvacuum object.

We use data from the Atacama Cosmology Telescope (ACT) DR4 to search for the presence of neutrino self-interaction in the cosmic microwave background. Consistent with prior works, the posterior distributions we find are bimodal, with one mode consistent with $\mathrm{\Lambda }\mathrm{CDM}$ and one where neutrinos strongly self-interact. By combining ACT data with large-scale information from WMAP, we find that a delayed onset of neutrino free streaming caused by significantly strong neutrino self-interaction is compatible with these data at the $2-3\sigma$ level. As seen in the past, the preference shifts to $\mathrm{\Lambda }\mathrm{CDM}$ with the inclusion of Planck data. We determine that the preference for strong neutrino self-interaction is largely driven by angular scales corresponding to $700\lesssim \ell \lesssim 1000$ in the ACT E-mode polarization data. This region is expected to be key to discriminate between neutrino self-interacting modes and will soon be probed with more sensitive data.

This study aims to test the validity of general relativity (GR) on kiloparsec scales by employing a newly compiled galaxy-scale strong gravitational lensing (SGL) sample. We utilize the distance sum rule within the Friedmann-Lemaître-Robertson-Walker metric to obtain cosmology-independent constraints on both the parametrized post-Newtonian parameter ${\gamma }_{\mathrm{PPN}}$ and the spatial curvature ${\mathrm{\Omega }}_k$, which overcomes the circularity problem induced by the presumption of a cosmological model grounded in GR. To calibrate the distances in the SGL systems, we introduce a novel nonparametric approach, artificial neural network (ANN), to reconstruct a smooth distance-redshift relation from the $\mathrm{Pantheon}+\text{sample}$ of type Ia supernovae. Our results show that ${\gamma }_{\mathrm{PPN}}=1.16_{-0.12}^{+0.15}$ and ${\mathrm{\Omega }}_k=0.89_{-1.00}^{+1.97}$, indicating a spatially flat universe with the conservation of GR (i.e., ${\mathrm{\Omega }}_k=0$ and ${\gamma }_{\mathrm{PPN}}=1$) is basically supported within $1\sigma$ confidence level. Assuming a zero spatial curvature, we find ${\gamma }_{\mathrm{PPN}}=1.09_{-0.10}^{+0.11}$, representing an agreement with the prediction of 1 from GR to a 9.6% precision. If we instead assume GR holds (i.e., ${\gamma }_{\mathrm{PPN}}=1$), the curvature parameter constraint can be further improved to be ${\mathrm{\Omega }}_k=0.11_{-0.47}^{+0.78}$. These resulting constraints demonstrate the effectiveness of our method in testing GR on galactic scales by combining observations of strong lensing and the distance-redshift relation reconstructed by ANN.

We consider the creation of kink-antikink pairs of a scalar field $\varphi$ by the scattering of classical wave packets of a second scalar field $\psi$ when there are no direct interactions between $\varphi$ and $\psi$. The creation becomes possible only due to a quantum field that interacts with both $\varphi$ and $\psi$. We scan parameter space and find it favorable for kink production when the initial wave packets have large total energy and wide spatial extent but scatter at low velocities.

With SU(3) gauge-Higgs theory as an example, we examine critically the idea that the confinement property in an SU(N) gauge-Higgs theory, with the Higgs field in the fundamental representation, persists in an unbroken SU(N-1) subgroup.

We discuss the quantum computation of dynamical chirality production in lattice gauge theory. Although the chirality of a lattice fermion is complicated in general dimensions, it can be simply formulated on a one-dimensional lattice. The chiral fermion formalism enables us to extract the physical part of the chirality production that would be interpreted as the chiral anomaly in the continuous theory. We demonstrate the computation of the $Z_2$ lattice gauge theory on a classical emulator.

We systematically study a family of loop quantizations for the classical Kruskal spacetimes using the effective description motivated from loop quantum gravity for four generic parameters, $c_o,m,{\delta }_b$, and ${\delta }_c$, where the latter two denote the polymerization parameters that capture the underlying quantum geometry. We focus on the family where polymerization parameters are constant on dynamical trajectories and of which the Ashtekar-Olmedo-Singh (AOS) and Corichi-Singh (CS) models appear as special cases. We study general features of singularity resolution in all these models due to quantum gravity effects and analytically extend the solutions across the white hole (WH) and black hole (BH) horizons to the exterior. We find that the leading term in the asymptotic expansion of the Kretschmann scalar is $r^{-4}$. However, for AOS and CS models, black holes with masses greater than solar mass, the dominant term behaves as $r^{-6}$ for the size of the observable Universe and our analysis can be used to phenomenologically constrain the choice of parameters for other models. In addition, one can uniquely fix the parameter $c_o$ by requiring that the Hawking temperature at the BH horizon to the leading order be consistent with its classical value for a macroscopic BH. Assuming that the BH and WH masses are of the same order, we are able to identify a family of choices of ${\delta }_b$ and ${\delta }_c$ which share all the desired properties of the AOS model.

We find the connection between relativistic and nonrelativistic string vacua in ${\mathrm{AdS}}_5\times {\mathrm{S}}^5$ in terms of a free parameter $c$ flow. First, we show that the famous relativistic BMN vacuum flows in the large $c$ parameter to an unphysical solution of the nonrelativistic theory. Then, we consider the simplest nonrelativistic vacuum, found in Fontanella and García [J. Phys. A 55, 085401 (2022)] (called BMN-like), and we identify its relativistic origin, namely a noncompact version of the folded string with zero spin, ignored in the past due to its infinite energy. We show that, once the critical closed B-field required by the nonrelativistic limit is included, the total energy of such relativistic solution is finite, and in the large $c$ parameter it precisely matches the one of the BMN-like string. We also analyze the case with spin in the transverse anti–de Sitter directions.

Lensed gravitational waves will offer new means to probe the distribution of matter in the Universe, complementary to electromagnetic signals. Lensed continuous gravitational waves provide new challenges and opportunities beyond those of transient compact binary coalescence. Here we consider continuous gravitational waves emitted by isolated neutron stars and lensed by Sgr ${\mathrm{A}}^{*}$, the supermassive black hole at the center of our Galaxy, a system observable by the next generation of gravitational wave detectors. We analyze the signatures of this system in detail, addressing parameter estimation and model selection. Future detectors can distinguish lensed continuous waves and measure their parameters with precision $\sim 1–10\%$ for sources within 2–4 Einstein radii of Sgr ${\mathrm{A}}^{*}$, depending on the source distance, thanks to the relative motion of the observer-lens-source system. The chances of observing strongly lensed neutron stars increase by one order of magnitude relative to previous estimates, thanks to the possibility of detecting lensed systems at several Einstein radii. Multiple images can be resolved with an angular accuracy $\sim 10$ mas, comparable to the best optical telescopes. Image localization probes deviations from axial symmetry and the existence of companions to Sgr ${\mathrm{A}}^{*}$ in regions complementary stellar orbits and black hole imaging. Our methods and many of our results extend to other lenses (e.g., Galactic substructure) and sources (e.g., long-lived inspiralling binaries), rendering lensed continuous gravitational waves into versatile probes of astrophysics and fundamental physics.

We present the results of an analysis of three maximal extensions of the Vaidya metric in Israel coordinates, a spherically symmetric solution to the Einstein field equations for the energy momentum tensor of pure radiation in the high-frequency approximation. This metric is necessary for various applications, such as describing the exterior geometry of a radiating star in astrophysics and studying possible formation of naked singularities in the geometry of spacetime. Contrary to the common Eddington-Finkelstein-Like coordinates, these maximal extensions, in Israel coordinates, are complete and cover the entirety of the Vaidya manifold. We develop three mass functions, one for each extension, and consider the qualitative characteristics of the three mass models and the surfaces of constant (dynamical) radius. We demonstrate that each maximal extension is null geodesically complete, which we assess by solving the radial null geodesics equation and forming the Penrose conformal diagram for each extension.

For the analysis of gravitational-wave signals, fast and accurate gravitational-waveform models are required. These enable us to obtain information on the system properties from compact binary mergers. In this article, we introduce the NRTidalv3 model, which contains a closed-form expression that describes tidal effects, focusing on the description of binary neutron star systems. The model improves upon previous versions by employing a larger set of numerical-relativity data for its calibration, by including high-mass ratio systems covering also a wider range of equations of state. It also takes into account dynamical tidal effects and the known post-Newtonian mass-ratio dependence of individual calibration parameters. We implemented the model in the publicly available lalsuite software library by augmenting different binary black hole waveform models (IMRPhenomD, IMRPhenomX, and SEOBNRv5_ROM). We test the validity of NRTidalv3 by comparing it with numerical-relativity waveforms, as well as other tidal models. Finally, we perform parameter estimation for GW170817 and GW190425 with the new tidal approximant and find overall consistent results with respect to previous studies.

When a brane is moving in a compact space, bulk-probing signals originating at the brane can arrive back at the brane outside the lightcone of the emitting event. In this paper, we study how adiabatic perturbations in the brane fluid, coupled to a bulk fluid, propagate in the moving brane. In the nondissipative regime, we find an effective sound speed for such perturbations, depending on the brane and bulk fluid energy densities, equations of state, and brane speed. In the tight-coupling approximation, the effective sound speed might be superluminal for brane and bulk fluids that satisfy the strong energy condition. This has immediate consequences for brane-world cosmology models.

Large blue tilted spectral index axionic isocurvature perturbations can be produced when the axion sector is far out of equilibrium during inflation through an initial Peccei-Quinn (PQ) symmetry breaking field displacement along a nearly flat direction in the effective potential. As a companion to a previous work, we present analytic formulas for the blue isocurvature spectrum for the case of the kinetic energy density of the PQ symmetry breaking field being larger than the quartic power of the final spontaneous PQ symmetry breaking scale. It corresponds to a regime in which the nonlinearities of the classical potential become important many times during the formation of the axion isocurvature quantum perturbations leading to interesting resonant behavior. One consequence of this nonlinearity-driven resonance is the chaotic nature of the map that links the underlying Lagrangian parameters to the isocurvature amplitudes. We point out an accidental duality symmetry between the perturbation equations and the background field equations that can be used to understand this. Finally, we present two types of analytic results. The first relies on a computation utilizing an effective potential wherein fast timescale fluctuations have been integrated out. The second is grounded in a functional ansatz, requiring only a limited set of fitting parameters. Both analytic results should be useful for carrying out forecasts and fits to the data.

The thermal plasma in the early Universe produced a stochastic gravitational wave (GW) background, which peaks today in the microwave regime and was dubbed the cosmic gravitational microwave background (CGMB). In previous works, only single graviton production processes that contribute to the CGMB have been considered. Here, we also investigate graviton pair production processes and show that these can lead to a significant contribution if the ratio between the maximum temperature and the Planck mass, $T_{\max }/m_{\mathrm{p}}$, divided by the internal coupling in the heat bath is large enough. As the dark matter freeze-in production mechanism is conceptually very similar to the GW production mechanism from the primordial thermal plasma, we refer to the latter as “GW freeze-in production.” We show that quantum gravity effects appear in single graviton production and are smaller by a factor $(T_{\max }/m_{\mathrm{p}}{)}^2$ than the leading order contribution. In our work, we explicitly compute the CGMB spectrum within a scalar model with quartic interaction.

In this work we present a unified model for the cosmological dark sector. The theory is based on a simple minimally coupled scalar field whose action only contains a canonical kinetic term and is invariant under transverse diffeomorphisms (TDiff). The model has the same number of free parameters as lambda cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$). We confront the predictions of the model at the background level with data from Planck 2018 CMB distance priors, $\mathrm{Pantheon}+$ and SH0ES SNIa distance moduli, BAO data points from 6dFGS, BOSS, eBOSS and DES and measurements of the Hubble parameter from cosmic chronometers. The model provides excellent results in the joint fit analysis, showing strong and very strong evidence compared to $\mathrm{\Lambda }\mathrm{CDM}$ in the Bayesian evidence and deviance information criterion (DIC) respectively. We also show that the Hubble tension between Planck 2018 and SH0ES measurements can be alleviated in the unified TDiff model although further analysis is still needed.

We study chirality production in the pseudoscalar inflation model of magnetogenesis, taking into account the Schwinger effect and particle collisions in plasma in the relaxation time approximation. We consider the Schwinger production of one Dirac fermion species by an Abelian gauge field in two cases: (i) fermions carry only the weak charge with respect to the U(1) group and (ii) they are also charged with respect to another strongly coupled gauge group. While the gradient-expansion formalism is employed for the description of the evolution of the gauge field, plasma is described by a hydrodynamical approach, which allows us to determine the number, energy density, and chirality of produced fermions. It is found that, while chirality production is very efficient for both weakly and strongly interacting fermions, the resulting gauge field is typically stronger in the case of strongly interacting fermions, due to suppression of the Schwinger conductivity by particle collisions.