We study black holes in the infrared sector of three-dimensional Hořava gravity. It is shown that black hole solutions with anti–de Sitter asymptotics are admissible only in the sector of the theory in which the scalar degree of freedom propagates infinitely fast. We derive the most general class of stationary, circularly symmetric, asymptotically anti–de Sitter black hole solutions. We also show that the theory admits black hole solutions with de Sitter and flat asymptotics, unlike three-dimensional general relativity. For all these cases, universal horizons may or may not exist depending on the choice of parameters. Solutions with de Sitter asymptotics can have universal horizons that lie beyond the de Sitter horizon.

In a four-dimensional spacetime, the DeWitt-Schwinger expansion of the effective action associated with a massive quantum field reduces, after renormalization and in the large mass limit, to a single term constructed from the purely geometrical Gilkey-DeWitt coefficient $a_3$ and its metric variation provides a good analytical approximation for the renormalized stress-energy tensor of the quantum field. Here, from the general expression of this tensor, we obtain analytically the renormalized stress-energy tensors of the massive scalar field, the massive Dirac field and the Proca field in Kerr-Newman spacetime. It should be noted that, even if, at first sight, the expressions obtained are complicated, their structure is in fact rather simple, involving naturally spacetime coordinates as well as the mass $M$, the charge $Q$ and the rotation parameter $a$ of the Kerr-Newman black hole and permitting us to recover rapidly the results already existing in the literature for the Schwarzschild, Reissner-Nordström and Kerr black holes (and to correct them in the latter case). In the absence of exact results in Kerr-Newman spacetime, our approximate renormalized stress-energy tensors could be very helpful, in particular to study the backreaction of massive quantum fields on this spacetime or on its quasinormal modes.

A celebrated result by Jacobson is the derivation of Einstein’s equations from Unruh’s temperature, the Bekenstein–Hawking entropy and the Clausius relation. This has been repeatedly taken as evidence for an interpretation of Einstein’s equations as equations of state for unknown degrees of freedom underlying the metric. We show that a different interpretation of Jacobson’s result is possible, which does not imply the existence of additional degrees of freedom, and follows only from the quantum properties of gravity. We introduce the notion of quantum gravitational Hadamard states, which give rise to the full local thermodynamics of gravity.

The linear perturbation of the Kerr black hole has been discussed by using the Newman-Penrose formalism, and the perturbed Weyl scalars, ${\psi }_0$ and ${\psi }_4$ can be obtained from the Teukolsky equation. In order to obtain the other Weyl scalars and the perturbed metric, a formalism was proposed by Chrzanowski and by Cohen and Kegeles to construct these quantities in a radiation gauge via the Hertz potential. As a simple example of the construction of the perturbed gravitational field with this formalism, we consider the gravitational field produced by a rotating circular ring around a Schwarzschild black hole. In the method by Chrzanowski, Cohen, and Kegeles, the metric is constructed in a radiation gauge via the Hertz potential, which is obtained from the solution of the Teukolsky equation. Since the solutions ${\psi }_0$ and ${\psi }_4$ of the Teukolsky equations are spin-2 quantities, the Hertz potential is determined up to its monopole and dipole modes. Without these lower modes, the constructed metric and Newman-Penrose Weyl scalars have unphysical jumps on the spherical surface at the radius of the ring. We find that the jumps of the imaginary parts of the Weyl scalars are cancelled when we add the angular momentum perturbation to the Hertz potential. Finally, by adding the mass perturbation and choosing the parameters which are related to the gauge freedom, we obtain the perturbed gravitational field which is smooth except on the equatorial plane outside the ring. We discuss the implication of these results to the problem of the computation of the gravitational self-force to the point particles in a radiation gauge.

We find a new instability in the four-dimensional Reissner-Nordström–de Sitter black holes against charged scalar perturbations with vanishing angular momentum, $l=0$. We show that such an instability is caused by superradiance. The instability does not occur for a larger angular index, as explicitly proved for $l=1$. Our results are obtained from a numerical investigation of the time-domain profiles of the perturbations.

We describe the quantum evolution of the vacuum Bianchi II universe in terms of the transition amplitude between two asymptotic quantum Kasner-like states. For large values of the momentum variable, the classical and quantum calculations give similar results. The difference occurs for small values of this variable due to the Heisenberg uncertainty principle. Our results can be used, to some extent, as a building block of the quantum evolution of the vacuum Bianchi IX universe.

In a previous paper, some of us studied general relativistic homogeneous gravitational collapses for dust and radiation, in which the density profile was replaced by an effective density justified by some quantum gravity models. It was found that the effective density introduces an effective pressure that becomes negative and dominant in the strong-field regime. With this setup, the central singularity is replaced by a bounce, after which the cloud starts expanding. Motivated by the fact that in the classical case homogeneous and inhomogeneous collapse models have different properties, here we extend our previous work to the inhomogeneous case. As in the quantum-inspired homogeneous collapse model, the classical central singularity is replaced by a bounce, but the inhomogeneities strongly affect the structure of the bounce curve and of the trapped region.

A quantum scalar field in anti–de Sitter space is considered in both static and Friedmann-Robertson-Walker coordinate systems. It is shown that quantum vacua corresponding to each of these coordinate systems are not unitary equivalent. A choice of a physical ground state between these vacua is discussed under different setups.

We analyze causal structures in Gauss-Bonnet gravity. It is known that Gauss-Bonnet gravity potentially has superluminal propagation of gravitons due to its noncanonical kinetic terms. In a theory with superluminal modes, an analysis of causality based on null curves makes no sense, and thus, we need to analyze them in a different way. In this paper, using the method of the characteristics, we analyze the causal structure in Gauss-Bonnet gravity. We have the result that, on a Killing horizon, gravitons can propagate in the null direction tangent to the Killing horizon. Therefore, a Killing horizon can be a causal edge as in the case of general relativity; i.e. a Killing horizon is the “event horizon” in the sense of causality. We also analyze causal structures on nonstationary solutions with $(D-2)$-dimensional maximal symmetry, including spherically symmetric and flat spaces. If the geometrical null energy condition, $R_{AB}{N}^A{N}^B\ge 0$ for any null vector $N^A$, is satisfied, the radial velocity of gravitons must be less than or equal to that of light. However, if the geometrical null energy condition is violated, gravitons can propagate faster than light. Hence, on an evaporating black hole where the geometrical null energy condition is expected not to hold, classical gravitons can escape from the “black hole” defined with null curves. That is, the causal structures become nontrivial. It may be one of the possible solutions for the information loss paradox of evaporating black holes.

In terms of gravitational solitons, we study the gravitational nonlinear effects of gravitational solitary waves such as Faraday rotation. Applying Pomeransky’s procedure for the inverse scattering method, which has been recently used for constructing stationary black hole solutions in five dimensions, to a cylindrical spacetime in four dimensions, we construct a new cylindrically symmetric soliton solution. This is the first example to be applied to the cylindrically symmetric case. In particular, we clarify the difference from Tomimatsu’s single soliton solution, which was constructed by Belinski-Zakharov’s procedure.

Anisotropic cosmologies are studied in the case where the matter source is given by the Skyrme model which is an effective description of low-energy QCD. The dynamical evolution of the Kantowski-Sachs and Bianchi-I universes are analyzed in depth. In both situations in order for solutions to exist and at the same time to avoid finite-time future singularities, bounds on the value of the cosmological constant and on the values of the Skyrme couplings must be set. The upper bound on the cosmological constant, which depends also on the initial conditions, is closely related to the fact that the baryons appear below 1 GeV. The lower bound on the cosmological constant and the bounds on the Skyrme couplings are due to the peculiar combination of nonlinear terms in the Skyrme model. It is worth pointing out that bounds on the Skyrme couplings occur in similar fashion both for the Kantowski-Sachs and for the Bianchi-I models, which are topologically completely different. Our results suggest that this behavior is intrinsic to the coupling of the Skyrme field to gravity rather than to a specific cosmological model.

A relativistic kinetic description for the irreversible thermodynamic process of gravitationally induced particle production is proposed in the context of an expanding Friedmann-Robertson-Walker geometry. We show that the covariant thermodynamic treatment referred to as “adiabatic” particle production provoked by the cosmic time-varying gravitational field has a consistent kinetic counterpart. The variation of the distribution function is associated to a noncollisional kinetic term of quantum-gravitational origin which is proportional to the ratio $\mathrm{\Gamma }/H$, where $\mathrm{\Gamma }$ is the gravitational particle production rate and $H$ is the Hubble parameter. For $\mathrm{\Gamma }\ll H$ the process is negligible and as should be expected it also vanishes (regardless of the value of $\mathrm{\Gamma }$) in the absence of gravitation. The resulting nonequilibrium distribution function has the same functional form of equilibrium with the evolution laws corrected by the particle production process. The macroscopic temperature evolution law is also kinetically derived for massive and massless particles. The present approach points to the possibility of an exact (semiclassical) quantum-gravitational kinetic treatment by incorporating backreaction effects in the cosmic background.

Scalar field with generalized kinetic interactions metamorphoses depending on its field value, ranging from a cosmological constant to stiff matter. We show that such a scalar field can give rise to temporal enhancement of the curvature perturbation in the primordial universe, leading to the efficient production of primordial black holes (PBHs) while the enhancement persists. If the inflation energy scale is high, those mini–black holes evaporate by the Hawking radiation much before big bang nucleosynthesis, and the effective reheating of the Universe is achieved by the black hole evaporation. The dominance of PBHs and the reheating by their evaporation modify the expansion history of the primordial universe. This results in a characteristic feature of the spectrum of primordial tensor modes in the DECIGO frequency band, opening an interesting possibility of testing the PBH reheating scenario by measuring the primordial tensor modes. If the inflation energy scale is low, the PBH mass can be much larger than the solar mass. In this case, the PBH is an interesting candidate for seeds for supermassive black holes residing in present galaxies.

We introduce EFTCAMB/EFTCosmoMC as publicly available patches to the commonly used camb/CosmoMC codes. We briefly describe the structure of the codes, their applicability and main features. To illustrate the use of these patches, we obtain constraints on parametrized pure effective field theory and designer $f(R)$ models, both on $\mathrm{\Lambda }\mathrm{CDM}$ and $w\mathrm{CDM}$ background expansion histories, using data from Planck temperature and lensing potential spectra, WMAP low-$\ell$ polarization spectra (WP), and baryon acoustic oscillations (BAO). Upon inspecting the theoretical stability of the models on the given background, we find nontrivial parameter spaces that we translate into viability priors. We use different combinations of data sets to show their individual effects on cosmological and model parameters. Our data analysis results show that, depending on the adopted data sets, in the $w\mathrm{CDM}$ background case these viability priors could dominate the marginalized posterior distributions. Interestingly, with $\mathrm{Planck}+\mathrm{WP}+\mathrm{BAO}+\mathrm{lensing}$ data, in $f(R)$ gravity models, we get very strong constraints on the constant dark energy equation of state, $w_0\in (-1,-0.9997)$ (95% C.L.).

Mini-black holes made of dark matter that can potentially form in the interior of neutron stars always have been thought to grow by accreting the matter of the core of the star via a spherical Bondi accretion. However, neutron stars have sometimes significant angular velocities that can in principle stall the spherical accretion and potentially change the conclusions derived about the time it takes for black holes to destroy a star. We study the effect of the star rotation on the growth of such black holes and the evolution of the black hole spin. Assuming no mechanisms of angular momentum evacuation, we find that even moderate rotation rates can in fact destroy spherical accretion at the early stages of the black hole growth. However, we demonstrate that the viscosity of nuclear matter can alleviate the effect of rotation, making it possible for the black hole to maintain spherical accretion while impeding the black hole from becoming maximally rotating.

In this paper we perform an amplitude analysis of essentially all published pion and kaon pair production data from two-photon collisions below 1.5 GeV. This includes all the high statistics results from Belle, as well as older data from Mark II at SLAC, CELLO at DESY, and Crystal Ball at SLAC. The purpose of this analysis is to provide as close to a model-independent determination of the $\gamma \gamma$ to meson pair amplitudes as possible. Having data with limited angular coverage, typically $|\cos \theta |<0.6–0.8$, and no polarization information for reactions in which spin is an essential complication, the determination of the underlying amplitudes might appear an intractable problem. However, imposing the basic constraints required by analyticity, unitarity, and crossing symmetry makes up for the experimentally missing information. Above 1.5 GeV multimeson production channels become important, and we have too little information to resolve the amplitudes. Nevertheless, below 1.5 GeV the two-photon production of hadron pairs serves as a paradigm for the application of $S$-matrix techniques. Final state interactions among the meson pairs are critical to this analysis. To fix these, we include the latest $\pi \pi \to \pi \pi$, $\overline{K}K$ scattering amplitudes given by dispersive analyses, supplemented in the $\overline{K}K$ threshold region by the recent precision Dalitz plot analysis from BABAR. With these hadronic amplitudes built into unitarity, we can constrain the overall description of $\gamma \gamma \to \pi \pi$ and $\overline{K}K$ data sets, both integrated and differential cross sections, including the high statistics charged and neutral pion, as well as $K_s{K}_s$, data from Belle. Since this analysis invokes coupled hadronic channels, having data on both $\pi \pi$ and $\overline{K}K$ reduces the solution space to essentially a single form in the region where these channels saturate unitarity. For the $\pi \pi$ channel, the separation of isospin-0 and -2 and helicity-0 and -2 components is complete. We present the partial wave amplitudes, show how well they fit all the available data, and give the two-photon couplings of scalar and tensor resonances that appear. These partial waves are important inputs into forthcoming dispersive calculations of hadronic light-by-light scattering.

The singly charged Higgs boson contribution to $0\nu 2\beta$ is neglected on grounds of couplings involving small masses and small nuclear matrix elements. We reconsider such contributions, but now in the light of QCD corrections and renormalization group evolution. It is found that the charged Higgs contribution is generically as large as (and at times significantly larger than) the other contributions and there can be large cancellations between contributions coming from different sources. This observation will have an important impact on the phenomenology.

We point out that recently discovered 3.5-keV line in x-ray spectra from various galaxy clusters and the Andromeda galaxy can be naturally explained by physics of a sector responsible for spontaneous supersymmetry breaking in models with $R$ parity. In this scenario, the source of this line could be decay of sgoldstino-scalar superpartner of massive gravitino. At the same time, the dominant dark matter component is stable gravitino whose mass is predicted to be about 0.25 GeV.

Within the framework of chiral effective field theory, we study various electromagnetic processes with light vector resonances: $K^{*}(892)\to K\gamma$, $e^{+}{e}^{-}\to K^{*}(892)K$, and the $\omega \pi {\gamma }^{*}$ form factors. With two multiplets of vector resonances being introduced, we fit the decay widths of $K^{*0}\to K^0\gamma$, $K^{*+}\to K^{+}\gamma$, and the pertinent measurements from the $e^{+}{e}^{-}\to K^{*\pm }(892)K^{\mp }$ cross sections, such as moduli and relative phases between the isoscalar and isovector components from the BABAR Collaboration, together with the $\omega \pi$ form factors from the NA60, SND, and CLEO collaborations. The values of resonance couplings, masses and widths of the excited vector states ${\rho }^{\prime }$ and ${\varphi }^{\prime }$ are then determined. The ${\omega }^{\prime }\text{−}{\varphi }^{\prime }$ mixing angle is discussed and turns out to be quite different from the ideal mixing case. Three sources of $SU(3)$ symmetry breaking effects in the $\mathrm{\Gamma }(K^{*}\to K\gamma )$ decays are identified and analyzed in detail.

We show that charged-lepton masses can be radiatively induced in multi-Higgs doublet models (NHDMs) through the renormalization group running of Yukawa couplings from high to low energies. Some extreme examples of electron and muon mass generation are discussed in the context of two- and three-Higgs-doublet models. It is also shown that quantum corrections to the Yukawa couplings can be naturally of the same order as the tree-level values. We also comment on the implications of considering extensions of NHDMs in which right-handed neutrinos are added.