The nonextremal Kerr black holes have been considered to be holographically dual to two-dimensional (2D) conformal field theories (CFTs). In this paper, we extend the holography to the case of an asymptotically anti–de Sitter (AdS) rotating charged black holes in $f(T)$ gravity, where $f(T)=T+\alpha T^2$, where $\alpha$ is a constant. We find that the scalar wave radial equation at the near-horizon region implies the existence of the 2D conformal symmetries. We note that the $2\pi$ identification of the azimuthal angle $\varphi$ in the black hole line element, corresponds to a spontaneous breaking of the conformal symmetry by left and right temperatures $T_L$ and $T_R$, respectively. We show that choosing proper central charges for the dual CFT, we produce exactly the macroscopic Bekenstein-Hawking entropy from the microscopic Cardy entropy for the dual CFT. These observations suggest that the rotating charged AdS black hole in $f(T)$ gravity is dual to a 2D CFT at finite temperatures $T_L$ and $T_R$ for a specific value of mass $M$, rotational, charge, and $f(T)$ parameters, $\mathrm{\Omega }$, $Q$, and $|\alpha |$, respectively.

In the presence of an ultralight bosonic field, spinning black holes are unstable to superradiance. The rotational energy of the black hole is converted into a nonaxisymmetric, oscillating boson cloud which dissipates through the emission of nearly monochromatic gravitational radiation. Thus, gravitational wave observations by ground- or space-based detectors can be used to probe the existence of dark particles weakly coupled to the Standard Model. In this work, we focus on massive vector bosons, which grow much faster through superradiance, and produce significantly stronger gravitational waves compared to the scalar case. We use techniques from black hole perturbation theory to compute the relativistically correct gravitational wave signal across the parameter space of different boson masses and black hole masses and spins. This fills in a gap in the literature between flatspace approximations, which underestimate the gravitational wave amplitude in the nonrelativistic limit and overestimate it in the relativistic regime, and time-domain calculations, which have only covered a limited part of the parameter space. We also identify parameter ranges where overtone superradiantly unstable modes will grow faster than the lower-frequency fundamental modes. Such cases will produce a distinct gravitational wave signal due to the beating of the simultaneously populated modes, which we compute.

Due to the nonindependence of entropy and thermodynamic volume for spherically symmetric black holes in the anti–de Sitter (AdS) spacetime, when applying the Ruppeiner thermodynamic geometry theory to these black holes, we often encounter an unavoidable problem of the singularity about the line element of thermodynamic geometry. In this paper, we propose a basic and natural scheme for dealing with the thermodynamic geometry of spherically symmetric AdS black holes. We point out that enthalpy, not internal energy, is the fundamental thermodynamic characteristic function for the Ruppeiner thermodynamic geometry. Based on this fact, we give the specific forms of the line element of thermodynamic geometry for the Schwarzschild AdS (SAdS) black hole in different phase spaces, and the results show that the thermodynamic curvatures obtained in different phase spaces are equivalent. It is shown that the thermodynamic curvature is negative which may be related to the information of attractive interaction between black hole molecules for the SAdS black hole. Meanwhile we also give an approximate expression of the thermodynamic curvature of the Schwarzschild black hole which shows that the black hole may be dominated by repulsion on the low temperature region and by attraction on the high temperature region phenomenologically or qualitatively.

We consider a recently proposed class of extended teleparallel theories of gravity, which entail a scalar field which is nonminimally coupled to the torsion of a flat, metric-compatible connection. This class of scalar-torsion theories of gravity is constructed in analogy to and as a direct extension of the well-studied class of scalar-curvature gravity theories, and has various common features, such as the conformal frame freedom. For this class we determine the parametrized post-Newtonian limit, both for a massive and for a massless scalar field. In the massive case, we determine the effective gravitational constant and the post-Newtonian parameter $\gamma$, both of which depend on the distance between the gravitating and test masses. In the massless case, we calculate the full set of parameters and find that only $\gamma$ and $\beta$ potentially deviate from their general relativity values. In particular, we find that for a minimally coupled scalar field, the theory becomes indistinguishable from general relativity at this level of the post-Newtonian approximation.

We study neutrino oscillations within the framework of extended theories of gravity. Based on the covariant reformulation of Pontecorvo’s formalism, we evaluate the oscillation probability of neutrinos propagating in static spacetimes described by gravitational actions quadratic in the curvature invariants. Calculations are carried out in the two-flavor approximation, for oscillations both in vacuum and matter. It is shown that the neutrino phase is sensitive to the violation of the strong equivalence principle. By way of illustration, we specialize our analysis to various extended models of gravity in order both to quantify such a violation and to understand how the characteristic free parameters of these models affect the neutrino phase. The possibility to fix new bounds on these parameters and to constrain extended theories of gravity is finally discussed.

The hadron-quark phase transition in the core of heavy neutron star (NS) has been studied. For the hadronic sector, we have used the lowest-order constraint variational method by employing $A{V}_{18}$, $A{V}_{14}$, $U{V}_{14}$, and Reid 68 two-body nucleon-nucleon forces supplemented by the phenomenological Urbana-type three-body force. We have adopted the MIT bag model as well as three-flavor version of the Nambu–Jona-Lasinio (NJL) model to describe the quark phase. The equation of state (EOS) of a hybrid star (HS) is presented by combining two EOS of the hadronic sector and quark sector of a star, which are derived from independent models or theories. The hadron-quark transition is constructed by considering a sharp phase transition, i.e., Maxwell construction. The structure of the HS is calculated and reported by solving Tolman-Oppenheimer-Volkoff equations. Finally, the radii and tidal deformability of purely NS and HS for the mass of $1.4M_{\odot }$ is computed, and new constraints on these quantities are checked. The maximum mass of the HS is found more than $2M_{\odot }$ for both the NJL and MIT bag models. However, the maximum mass of $1.796M_{\odot }$ ($1.896M_{\odot }$) was the best result that would be calculated for a stable HS with the pure quark core within the MIT (NJL) model. All the hybrid EOS fulfill the constraints on radii and tidal deformability extracted from the binary GW170817 for HSs. A comprehensive analysis on the structure of purely NS and HS and also compactness, tidal Love number, and tidal deformability for the star with the mass of $1.4M_{\odot }$ has been conducted for various EOS of the hadron sector and several parameter sets of the quark EOS. The results achieved in this study are in good concurrence with the other calculations reported on this subject.

We present an exactly solvable example of coherent quantum interference effects in the creation of electron-positron pairs from the collision of a photon with ultrashort laser pulses. Being characterized entirely by null, or lightlike, directions, this setup realizes an all-optical double-slit in the “null” domain, and exhibits features both in common with, and distinct from, a time domain double-slit (Ramsey interferometer). We show that by tailoring the order and amplitude of the pulses one can control signatures of both quantum and classical physics in the produced positron spectrum.

We discuss the subleading power corrections to one-jet production processes in $N$-jettiness subtraction using vector-boson plus jet production as an example. We analytically derive the next-to-leading power (NLP) leading logarithmic corrections through $\mathcal{O}({\alpha }_S)$ in perturbative QCD and outline the calculation of the next-to-leading logarithmic corrections. Our result is differential in the jet transverse momentum and rapidity, and in the vector boson momentum squared and rapidity. We present simple formulas that separate the NLP corrections into universal factors valid for any one-jet cross section and process-dependent matrix-element corrections. We discuss in detail features of the NLP corrections such as the process independence of the leading-logarithmic result that occurs due to the factorization of matrix elements in the subleading soft limit, the occurrence of poles in the nonhemisphere soft function at NLP, and the cancellation of potential $\sqrt{{\mathcal{T}}_1/Q}$ corrections to the $N$-jettiness factorization theorem. We validate our analytic result by comparing them to numerically fitted coefficients, finding good agreement for both the inclusive and the differential cross sections. The size of the power corrections for different definitions of ${\mathcal{T}}_1$ is studied.

We discuss a minimal flavor model with twin modular symmetries, leading to trimaximal ${\mathrm{TM}}_1$ lepton mixing in which the first column of the tri-bimaximal lepton mixing matrix is preserved. The model involves two modular $S_4$ groups, one acting in the neutrino sector, associated with a modulus field value ${\tau }_{SU}$ with residual $Z_2^{SU}$ symmetry, and one acting in the charged lepton sector, associated with a modulus field value ${\tau }_T$ with residual $Z_3^T$ symmetry. Apart from the predictions of ${\mathrm{TM}}_1$ mixing, the model leads to a new neutrino mass sum rule which implies lower bounds on neutrino masses close to current limits from neutrinoless double beta decay experiments and cosmology.

One reason for the well-known fact that the complex Langevin (CL) method sometimes fails to converge or converges to the wrong limit has been identified long ago: it is insufficient decay of the probability density either near infinity or near poles of the drift, leading to boundary terms that spoil the formal argument for correctness. To gain a deeper understanding of this phenomenon, in a previous paper [Phys. Rev. D 99, 014512 (2019)] we have studied the emergence of such boundary terms thoroughly in a simple model, where analytic results can be compared with numerics. Here we continue this type of analysis for more physically interesting models, focusing on the boundaries at infinity. We start with Abelian and non-Abelian one-plaquette models, and then we proceed to a Polyakov chain model and finally to high density QCD and the 3D XY model. We show that the direct estimation of the systematic error of the CL method using boundary terms is in principle possible.

We study the hidden-charm pentaquark states $udsc\overline{c}$ with spins $1/2$, $3/2$, and $5/2$ within the QCD sum-rule approach. First, we construct the currents for the particular configuration of pentaquark states that consist of the flavor singlet three-quark cluster $uds$ of spins $1/2$ and $3/2$ and the two-quark cluster $\overline{c}c$ of spin 1, where both clusters are in a color-octet state. From the QCD sum rules obtained by the operator product expansion up to dimension-10 condensates, the extracted masses for the pentaquark states $uds\text{−}\overline{c}c$ are about 4.6 GeV (5.6 GeV) for spin $1/2^{\pm }$, about 5.1 GeV (6.0 GeV) for spin $3/2^{\pm }$, about 6.1 GeV (5.9 GeV) for spin $5/2^{\pm }$, where the masses of the positive parity states are given in parentheses. Additionally, based on the flavor singlet pentaquark states, it is also shown that other pentaquark states of clusters like $udc\text{−}\overline{c}s$ and $usc\text{−}\overline{c}d$ lead to masses similar to the $uds\text{−}\overline{c}c$ case within error bars. Furthermore, in order to see whether any of the states, observed by the LHCb Collaboration, could be understood as the pentaquark of two clusters in the color-octet state, we study the pentaquark formed by the two clusters $udc\text{−}\overline{c}u$, where the three-quark cluster is assumed to have the same flavor structure as the above $uds$ cluster. We come to the conclusion that if the observed pentaquark will be found to have spin $1/2$ and negative parity, then it could be described as a state of two color-octet clusters.

We discuss the comments made by Emanuel Gallo and Thomas Mädler on our papers [Gen. Relativ. Gravit. 49, 77 (2017) and Phys. Rev. D 99, 084054 (2019)] on boosted Kerr black holes in general relativity. We considered their criticisms carefully, as they added a significant contribution to the question of boosted Kerr black holes in general relativity examined in our papers. Here, we expand on further results of our papers that were not duly included in the published papers, as noticed by Gallo and Mädler. We now consider the complete asymptotic Lorentz transformations of Robinson-Trautman (RT) coordinates to Bondi-Sachs (BS) asymptotic coordinates of a radiative RT spacetime, which include the perturbation term of the boosted RT metric corresponding to the Lense-Thirring rotation originating from the Kerr metric. The transformation of the rotation parameter $\omega$ as the RT coordinates transform to BS coordinates is obtained, as well as the form of the boosted Kerr metric where we make use of the complete asymptotic Lorentz transformation.

We discuss a recently presented boosted Kerr black hole solution which had already been used by other authors. This boosted metric is based on wrong assumptions regarding asymptotic inertial observers, and moreover the performed boost is not a proper Lorentz transformation. This Comment aims to clarify some of the issues that arise when boosting black holes and the care required to interpret them.

In the loop quantum gravity context, there have been numerous proposals to quantize the reduced phase space of a black hole and develop a classical effective description for its interior which eventually resolves the singularity. However, little progress has been made toward understanding the relation between such quantum/effective minisuperspace models and what would be the spherically symmetric sector of loop quantum gravity. In particular, it is not clear whether one can extract the phenomenological predictions obtained in minisuperspace models, such as the singularity resolution and the spacetime continuation beyond the singularity, based on results in full loop quantum gravity. In this paper, we present an attempt in this direction in the context of Kantowski-Sachs spacetime, through the proposal of two new effective Hamiltonians for the reduced classical model. The first is derived using Thiemann classical identities for the regularized expressions, while the second is obtained as a first approximation of the expectation value of a Hamiltonian operator in loop quantum gravity in a semiclassical state peaked on the Kantowski-Sachs initial data. We then proceed with a detailed analysis of the dynamics they generate and compare them with the Hamiltonian derived in general relativity and the common effective Hamiltonian proposed in earlier literature.

Different versions of consistent canonical realizations of hypersurface deformations of spherically symmetric spacetimes have been derived in models of loop quantum gravity, modifying the classical dynamics and sometimes also the structure of spacetime. Based on a canonical version of effective field theory, this paper provides a unified treatment, showing that modified spacetime structures are generic in this setting. The special case of Euclidean gravity demonstrates agreement also with existing operator calculations.

The relative transverse velocity of a lens with respect to the source star in gravitational lensing results in a frequency shift in the light rays passing by a lens. We propose using this relativistic effect for measuring the relative velocity of the lens with respect to the source star in gravitational microlensing. High precision spectrographs with the accuracy of detecting the relative frequency shift in the order of ${10}^{-11}$ will enable us to measure this effect in the microlensing events. The spectrographs such as ESPRESSO are going to be used for detecting exoplanets with the accuracy of the radial velocity of $0.1\mathrm{m}/\mathrm{s}$. This kind of instrument can be used in follow-up observations of the microlensing events. Combining the spectroscopic observation with the parallax measurements of microlensing events from space and proper motion of the source stars with GAIA telescope enables us to measure all the parameters of the microlensing events. The result would be measuring the mass and the transverse velocity of lenses with the masses in the range of the black holes to the free-floating planets.

We present calculations for the anticipated shadow sizes of Sgr A* and the supermassive black hole in the galaxy M87 in the context of the MOG modified theory of gravitation (also known as Scalar-Tensor–Vector-Gravity). We demonstrate that mass estimates derived from stellar and gas dynamics in the vicinity of these black holes are the Newtonian masses of the black holes even in the MOG theory. Consequently, shadow sizes increase as a function of the key dimensionless MOG parameter $\alpha$ that characterizes the variable gravitational coupling coefficient $G$ and may offer an observational means to distinguish the MOG theory from standard general relativity.

Extra dimensions, which led to the foundation and inception of string theory, provide an elegant approach to force unification. With bulk curvature as high as the Planck scale, higher curvature terms, namely, $f(R)$ gravity, seem to be a natural addendum in the bulk action. These can not only pass the classic tests of general relativity but also serve as potential alternatives to dark matter and dark energy. With interesting implications in inflationary cosmology, gravitational waves, and particle phenomenology, it is worth exploring the impact of extra dimensions and $f(R)$ gravity in black hole accretion. Various classes of black hole solutions have been derived that bear nontrivial imprints of these ultraviolet corrections to general relativity. This, in turn, gets engraved in the continuum spectrum emitted by the accretion disk around black holes. Since the near horizon regime of supermassive black holes manifest maximum curvature effects, we compare the theoretical estimates of disk luminosity with quasar optical data to discern the effect of the modified background on the spectrum. In particular, we explore a certain class of black hole solution bearing a striking resemblance to the well-known Reissner-Nordström–de Sitter/anti–de Sitter/flat spacetime, which, unlike general relativity, can also accommodate a negative charge parameter. By computing error estimators like chi square, Nash-Sutcliffe efficiency, index of agreement, etc., we infer that optical observations of quasars favor a negative charge parameter, which can be a possible indicator of extra dimensions. The analysis also supports an asymptotically de Sitter spacetime with an estimate of the magnitude of the cosmological constant whose origin is solely attributed to $f(R)$ gravity in higher dimensions.

When formulated in terms of connection and coframes, and in the time gauge, the phase space of general relativity consists of a pair of conjugate fields: the flux 2-form and the Ashtekar connection. On this phase-space, one has to impose the Gauss constraints, the vector, and scalar Hamiltonian constraints. These are respectively generating local SU(2) gauge transformations, spatial diffeomorphisms, and time diffeomorphisms. We write the Gauss and space diffeomorphism constraints as conservation laws for a set of boundary charges, representing spin and momenta, respectively. We prove that these kinematical charges generate a local Poincaré ISU(2) symmetry algebra. This gives strong support to the recent proposal of Poincaré charge networks as a new realm for discretized general relativity [Classical Quantum Gravity 36, 195014 (2019)].

Scale invariant theories of gravity give a compelling explanation to the early and late time acceleration of the Universe. Unlike most scalar-tensor theories, fifth forces are absent, and it would therefore seem impossible to distinguish scale invariant gravity from general relativity. We show that the ringdown of a Schwarschild–de Sitter black hole may have a set of massive modes which are characteristic of scale invariant gravity. In principle these new modes can be used to distinguish scale invariant gravity from general relativity. In practice, we discuss the obstacles to generating these new massive modes and their detectability with future gravitational wave experiments but also speculate on their role in Kerr black holes.