The discovery of gravitational waves, which are ripples of space-time itself, opened a new window to test general relativity, because it predicts that there are only plus and cross polarizations for gravitational waves. For alternative theories of gravity, there may be up to six polarizations. The measurement of the polarization is one of the major scientific goals for future gravitational wave detectors. To evaluate the capability of the detector, we need to use the frequency dependent response functions averaged over the source direction and polarization angle. We derive the full analytical formulas of the averaged response functions for all six possible polarizations and present their asymptotic behaviors based on these analytical formulas. Compared with the numerical simulation, the full analytical formulas are more efficient and valid for any equal-arm interferometric gravitational wave detector without optical cavities in the arms and for a time-delay-interferometry Michelson combination.

We study the perturbative stability of magnetic black holes in a general class of nonlinear electrodynamics, where the Lagrangian is given by a general function of the field strength of electromagnetic field $F_{\mu \nu }$ and its Hodge dual ${\tilde{F}}_{\mu \nu }$. We derive sufficient conditions for the stability of the black holes. We apply the stability conditions to Bardeen’s regular black holes, black holes in Euler–Heisenberg theory, and black holes in Born–Infeld theory. As a result, we obtain a sufficient condition for the stability of Bardeen’s black holes, which restricts $F_{\mu \nu }{\tilde{F}}^{\mu \nu }$ dependence of the Lagrangian. We also show that black holes in Euler–Heisenberg theory are stable for a sufficiently small magnetic charge. Moreover, we prove the stability of black holes in the Born–Infeld electrodynamics even when including $F_{\mu \nu }{\tilde{F}}^{\mu \nu }$ dependence.

We consider general relativity with a cosmological constant minimally coupled to the electromagnetic field and assume that the four-dimensional spacetime manifold is a warped product of two surfaces with Lorentzian and Euclidean signature metrics. Field equations imply that at least one of the surfaces must be of constant curvature leading to the symmetry of the metric (“spontaneous symmetry emergence”). We classify all global solutions in the case when the Lorentzian surface is of constant curvature (case C). These solutions are invariant with respect to the Lorentz $\mathbb{S}\mathbb{O}(1,2)$ or Poincare $\mathbb{I}\mathbb{O}(1,1)$ groups acting on the Lorentzian surface.

In continuation of our previous study [C. A. Benavides-Gallego, A. Abdujabbarov, D. Malafarina, B. Ahmedov, and C. Bambi, Phys. Rev. D 99, 044012 (2019)], we investigate the motion of charged particles in the $\gamma$-metric. We provide some examples of curled trajectories in the equatorial plane and escape trajectories outside the equatorial plane. Finally, we consider harmonic oscillations due to small displacements from stable circular orbits on the equatorial plane and compute the epicyclic frequencies for different values of deformation parameter and magnetic field.

We study influence of scalar fields on nonlinear electrodynamics spacetimes. The investigation is carried out using both test and gravitating scalar fields. After revisiting Einstein–Maxwell scalar field solutions we focus on analytic investigation of nonlinear electrodynamics scalar field spacetimes, especially the square root Lagrangian model. The main motivation being to understand whether certain specific signatures of scalar fields are preserved when nonlinear electrodynamics as an additional source is considered. We show that the regularity of horizon which is spoiled by scalar field in spherically symmetric static scalar-vacuum spacetimes is not improved by including nonlinear electrodynamics or other sources satisfying certain condition. We confirm these findings using test scalar field that enables us to go beyond spherical symmetry.

We consider the Stokes parameters’ frequency spectral distortions arising due to Compton scattering of the anisotropic cosmic microwave background (CMB) radiation, the Sunyaev-Zel’dovich effect (SZ), towards clusters of galaxies. We single out a very special type of such distortions and find simple analytical formulas for them. We show that this kind of distortion has a very distinctive spectral shape and can be separated from other kinds of contaminants. We demonstrate that this effect gives us an opportunity for an independent estimation of the low-multipole angular CMB anisotropies, such as the dipole, the quadrupole, and the octupole. We also show that, using distorted signals from nearby and distant clusters, one can distinguish between the Sachs-Wolfe and the integrated Sachs-Wolfe effects. The detection of such distortions can be feasible with high-angular-resolution and high-sensitivity space missions, such as the upcoming Millimetron Space Observatory experiment.

After the discovery of Fermi bubbles and the excess of gamma-ray emission, the Galactic Center has received increasing attention with the aim to understand its role in the origin and acceleration of primary cosmic rays. Based on a diffusion/reacceleration model, we use the galprop software to solve the diffusion equation for the cosmic rays and compare the results with the cosmic-ray spectrum, motivated by the relationship between several energetic sources at the Galactic Center and the generated diffuse GeV-TeV gamma rays. We calculate the cosmic ray distribution, gamma-ray flux from the Galactic Center and explore its contribution on the spectrum and chemical composition of cosmic rays observed on Earth. We also discuss the effects of nuclei interactions with different interstellar gas models.

X-ray reflection spectroscopy is a powerful tool to probe the strong gravity region around black holes, but the available relativistic reflection models have a number of simplifications that lead to systematic uncertainties (not fully under control) in the measurement of the properties of a source. In Paper I, we considered the case of an optically thin plunging region, and we studied the impact of the radiation produced by the other side of the disk or circling the black hole one or more times. In the present paper, we discuss the case of an optically thick plunging region, and we study the impact of the reflection spectrum of the plunging gas. We show that the contribution of such radiation is more important for low and negative values of the black hole spin parameter and large values of the viewing angle, and it decreases significantly as the spin parameter increases and the inclination angle decreases. While the estimate of some parameters may be affected by the reflection spectrum of the plunging gas if this is not included in the theoretical model, we find that such radiation does not appreciably limit our capability of testing the Kerr black hole hypothesis.

The exchange of two neutrinos at one loop leads to a long-range parity-violating force between fermions. We explore the two-neutrino force in the backdrop of atomic physics. We point out that this is the largest parity-violating long-range force in the Standard Model and calculate the effect of this force in experiments that probe atomic parity violation by measuring optical rotation of light as it passes through a sample of vaporized atoms. We perform explicit calculations for the hydrogen atom to demonstrate this effect. Although we find that the effect is too small to be observed in hydrogen in the foreseeable future, our approach may be applied to other setups where long-range parity violation is large enough to be probed experimentally.

We investigate the possibility that a minimal realization of left-right supersymmetry can be reachable at a high-energy upgrade of the LHC, expected to operate at a center-of-mass energy of 27 TeV. This minimal scenario has a relatively light $SU(2{)}_R$ doubly charged Higgs boson, which could decay dominantly into tau-lepton pairs. We explore the associated signals comprised of at least three hadronically decaying taus, or with at least two hadronic taus and one same-sign-same-flavor charged lepton pair. Our analysis shows that the former signature is challenging to use for getting handles on the signal due to the large corresponding background, and that the latter one can lead to a handful of new physics events in an almost backgroundfree environment. We however find that a signal comprised of three hadronically decaying tau leptons is likely to be observed at a low luminosity of proton-proton collisions at a 27 TeV upgrade of the LHC.

The main objective of our article [A. A. Garcia-Diaz and G. Gutierrez-Cano, Phys. Rev. D 100, 064068 (2019)] was the establishing of the existence of an infinite class of electrically charged solutions to Einstein–nonlinear electrodynamics (NLE) equations, which is determined for any imaginable set of structural functions $Q\mathrm{s}$ without any integration. The curvature invariants (CI) $\{S,{\mathrm{\Psi }}_2,R\}$, related to the quadratic Riemann invariants, are evaluated in terms of $Q$, and its derivatives $\dot{Q}$, and $\ddot{Q}$. The necessary and sufficient conditions for the regularity at the center of the CI, ${\lim }_{r\to 0}\{S,{\mathrm{\Psi }}_2,R\}=\{0,0,4\mathrm{\Lambda }+4\mathcal{L}(0)\}$, of the NLE electric $(\mathcal{E}≔q_0{F}_{rt})$ solutions are: ${\lim }_{r\to 0}\{\mathcal{E},\dot{\mathcal{E}},\ddot{\mathcal{E}}\}=\{0,0,0\}$, and ${\lim }_{r\to 0}\{Q,\dot{Q},\ddot{Q}\}=\{0,0,2\}$. Moreover, in the theorem on linear superposition of solutions $Q({\mathcal{E}}_i)$, with the use of a single Kottler solution $Q_K$, $Q(r)=Q_K+{\sum }_i{C}_{i}Q({\mathcal{E}}_i)$, the redundancy in introducing sums of partial ${\mathrm{\Lambda }}_i$, $C_i$, 1’s, and $m_i$, drops out.

It is argued that in the paper by A. A. Garcia-Diaz and G. Gutierrez-Cano [Phys. Rev. D 100, 064068 (2019)] on nonlinear electrodynamics coupled to general relativity, along with some interesting results and useful observations, many statements are either inaccurate or incomplete. In particular, the authors only consider solutions with an electric charge, whereas their magnetic counterparts have features of equal interest, both similar to and different from those of electric ones. Moreover, it is not mentioned that in electric solutions with a regular center the Lagrangian function $L(f)$ ($f=F_{\mu \nu }{F}^{\mu \nu }$) cannot have a Maxwell weak-field limit. The observation on superpositions of regular solutions suffers some inaccuracies. The present Comment tries to fill these gaps and to provide necessary corrections.

Recently it was found that, due to Weyl anomaly, an external magnetic field can induce anomalous currents near a boundary. In this paper, we study anomalous currents for complex scalars and Dirac fields in general dimensions. We develop a perturbation method to calculate Green’s function in the spacetime with boundaries. By applying this method, we obtain anomalous currents up to the linear order of magnetic fields in a half space and in a strip. To the best of our knowledge, the results for Dirac fermions and for strips are new. It is remarkable that, unlike the scalars and holographic boundary conformal field theory, the anomalous currents of Dirac fields are independent of boundary conditions in general dimensions. Besides, the currents of Dirac fields are always larger than those of complex scalars. Finally, we find an exact formal expression of the anomalous current in a half space. The result is expressed in momentum integrals, which can be evaluated numerically. We find that the mass suppresses the anomalous currents as expected.

A new class of conformal field theories is presented, where the background gravitational field is conformally flat. Conformally flat (CF) spacetimes enjoy conformal properties quite similar to the ones of flat spacetime. The conformal isometry group is of maximal rank and the conformal Killing vectors in conformally flat coordinates are exactly the same as the ones of flat spacetime. In this work, a new concept of distance is introduced, the conformal distance, which transforms covariantly under all conformal isometries of the CF space. It is shown that precisely for CF spacetimes, an adequate power of the said conformal distance is a solution of the nonminimal d’Alembert equation.

The study of the Unruh effect naturally raises the interest for a deeper understanding of the analogy between temperature and acceleration. A recurring question is whether an accelerated frame can be distinguished from an inertial thermal bath in pure thermodynamic experiments; such problem has been approached in the literature and a consensus is yet to be fully reached. In the present work, we use the open quantum system formalism to investigate the case where both acceleration and background temperature are present. We find the asymptotic state density and entanglement generation from the Markovian evolution of accelerated qubits interacting with a thermal state of the external scalar field. Our results suggest that there is a very small asymmetry on the effects of the Unruh and background temperatures. Addressing the nonzero background temperature case is of both theoretical and phenomenological interest, thus the authors hope to enrich the existing discussions on the topic.

In this article we further investigate the construction of graph coherent states, first introduced in [M. Assanioussi, Phys. Rev. D 98, 045016 (2018)], in the context of loop quantum gravity. We specifically investigate the possibility of defining a family of graph coherent states adapted to the canonical loop quantum gravity Hamiltonian. After discussing various aspects of the general framework and the choice of operators, we use the Euclidean part of the Hamiltonian operator to propose a generator of the generalized canonical structure, necessary to define the coherent states. We then apply the construction procedure, leading to a new family of graph coherent states partially adapted to the gravity Hamiltonian in loop quantum gravity.

We propose new massive gravity theories with 5 dynamical degrees of freedom. We evade uniqueness theorems regarding the form of the kinetic and potential terms by adopting the “generalized massive gravity” framework, where a global translation invariance is broken. By exploiting the rotation symmetry in the field space, we determine two novel classes of theories. The first one is an extension of generalized massive gravity with a nonminimal coupling. On the other hand, the second theory produces a mass term that is different from de Rham, Gabadadze, Tolley construction and trivially has 5 degrees of freedom. Both theories allows for stable cosmological solutions without infinite strong coupling, which are free of ghost and gradient instabilities.

$\ell$-boson stars are static, spherical, multifield self-gravitating solitons. They are asymptotically flat, finite energy solutions of Einstein’s gravity minimally coupled to an odd number of massive, complex scalar fields. A previous study assessed the stability of $\ell$-boson stars under spherical perturbations, finding that there are both stable and unstable branches of solutions, as for single-field boson stars ($\ell =0$). In this work we probe the stability of $\ell$-boson stars against nonspherical perturbations by performing numerical evolutions of the Einstein-Klein-Gordon system, with a 3D code. For the timescales explored, the $\ell$-boson stars belonging to the spherical stable branch do not exhibit measurable growing modes. We find, however, evidence of zero modes; that is, nonspherical perturbations that neither grow nor decay. This suggests the branching off toward a larger family of equilibrium solutions: we conjecture that $\ell$-boson stars are the enhanced isometry point of a larger family of static (and possibly stationary), nonspherical multifield self-gravitating solitons.

We analyze the scalar radiation emitted by a source in geodesic circular orbits around a Schwarzschild–de Sitter black hole. We obtain the emitted power using quantum field theory in curved spacetimes framework at tree level. We compare our results with the scalar synchrotron radiation in Schwarzschild spacetime.

We study the new massive gravity extended by the curvature cubed invariant and the cosmological constant (C.C.) using the tree-level exchange amplitudes on a maximally symmetric space-time. We identify the parameter space, consisting of the ratio between C.C. and graviton mass squared and the relative coupling strength between curvature squared and cubed invariants, for which the massive spin-2 is a ghost. Different phases of this model are also discussed.