Boson stars, self-gravitating objects made of a complex scalar field, have been proposed as simple models for very different scenarios, ranging from galaxy dark matter to black hole mimickers. Here we focus on a very compact type of boson stars to study binary mergers by varying different parameters, namely the phase shift, the direction of rotation, and the angular momentum. Our aim is to investigate the properties of the object resulting from the merger in these different scenarios by means of numerical evolutions. These simulations, performed by using a modification of the covariant conformal Z4 formalism of the Einstein equations that does not require the algebraic enforcing of any constraint, indicate that the final state after a head-on collision of low mass boson stars is another boson star. However, almost complete annihilation of the stars occurs during the merger of a boson-antiboson pair. The merger of orbiting boson stars form a rotating bar that quickly relaxes to a nonrotating boson star.

Quantum gravitational effects in black hole spacetimes with a cosmological constant $\mathrm{\Lambda }$ are considered. The effective quantum spacetimes for the black holes are constructed by taking into account the renormalization group improvement of classical solutions obtained in the framework of unimodular gravity (a theory which is identical to general relativity at a classical level). This allows us to avoid the usual divergences associated with the presence of a running $\mathrm{\Lambda }$. The horizons and causal structure of the improved black holes are discussed, taking into account the current observational bounds for the cosmological constant. It is shown that the resulting effective quantum black hole spacetimes are always devoid of singularities.

We apply the principles of quantum mechanics and quantum cosmology to predict probabilities for our local observations of a Universe undergoing false-vacuum eternal inflation. At a sufficiently fine-grained level, histories of the Universe describe a mosaic of bubble universes separated by inflationary regions. We show that predictions for local observations can be obtained directly from sets of much coarser-grained histories which only follow a single bubble. These coarse-grained histories contain neither information about our unobservable location nor about the unobservable large-scale structure outside our own bubble. Applied to a landscape of false vacua in the no-boundary state, we predict our local Universe emerged from the dominant decay channel of the lowest-energy false vacuum. We compare and contrast this framework for prediction based on quantum cosmology with traditional approaches to the measure problem in cosmology.

Any particle that is charged under $SU(3{)}_C$ and $U(1{)}_{\mathrm{EM}}$ can mediate the $gg\to \gamma \gamma$ process through loops. Near the threshold for the new particle pair production, gauge boson exchanges necessitate the resummation of ladder diagrams. We discuss the leading log order matching of the one-loop result with the nonrelativistic effective theory resummed result. We show how the diphoton invariant mass spectrum varies depending on decay width, color representation, and electric charge of the new particle. The exclusion limits on the product of $SU(3{)}_C$ and $U(1{)}_{\mathrm{EM}}$ charges of the new scalar or fermion particle are obtained from current LHC data.

In order to localize fermions on branes with codimension 1, one usually introduces the Yukawa coupling between fermions and background scalar fields or the recently proposed derivative fermion-scalar coupling [Phys. Rev. D 89, 086001 (2014)]. In this paper, we explore the coupling between a spinor field $\mathrm{\Psi }$ and the scalar curvature of spacetime $R$, $\eta \mathrm{\Psi }{\mathrm{\Gamma }}^M{\partial }_{M}F(R){\gamma }^5\overline{\mathrm{\Psi }}$ with $F(R)$ a function of $R$, to investigate the localization of the fermion. Because of the $Z_2$ symmetry of the extra dimension, the new coupling mechanism proposed here can easily deal with the problem encountered in the Yukawa coupling with even background scalar fields. More importantly, the new mechanism will also work for branes without background scalar fields. By investigating three examples, we find that fermions can be localized on branes with the new mechanism. We also study the case of both couplings of fermions, those with the scalar field and those with the curvature.

We present a simple prescription for the rotation of polarization produced by a relativistically moving gravitational lens, applicable to arbitrary deflection angle and arbitrary velocity of the lens. When geometric optics is applicable, two independent components contribute to the total rotation of polarization: (i) in the frame of the lens the polarization vector experiences minimal rotation defined by the deflection angle (as measured by a set of remote observers, or no rotation if defined in terms of a parallel-propagated tetrad); (ii) the effect of the motion of the lens on the polarization can be taken into account exactly using special-relativistic Lorentz transformation of polarization. The effects of the gravitational lensing are thus parametrized by the deflection angle of the null geodesics (not necessarily small) and the motion of the lens (not necessarily with velocities much smaller than that of light).

According to the conjecture “complexity equals action,” the complexity of a holographic state is equal to the action of a Wheeler-DeWitt (WDW) patch of black holes in anti–de Sitter space. In this paper we calculate the action growth of charged black holes with a single horizon, paying attention to the contribution from a spacelike singularity inside the horizon. We consider two kinds of such charged black holes: one is a charged dilaton black hole, and the other is a Born-Infeld black hole with ${\beta }^2{Q}^2<1/4$. In both cases, although an electric charge appears in the black hole solutions, the inner horizon is absent; instead a spacelike singularity appears inside the horizon. We find that the action growth of the WDW patch of the charged black hole is finite and satisfies the Lloyd bound. As a check, we also calculate the action growth of a charged black hole with a phantom Maxwell field. In this case, although the contributions from the bulk integral and the spacelike singularity are individually divergent, these two divergences just cancel each other and a finite action growth is obtained. But in this case, the Lloyd bound is violated as expected.

By post-Newtonian (PN) expanding the well-known, factorized and resummed, effective-one-body energy flux for circularized binaries, we show that (i) because of the presence of the resummed tail factor, the 4.5PN-accurate tails-of-tails-of-tails contribution to the energy flux recently computed by Marchand et al. [Classical Quantum Gravity 33, 244003 (2016)] is actually contained in the resummed expression; this is also the case of the next-to-leading-order tail-induced spin-orbit term of Marsat et al. [Classical Quantum Gravity 31, 025023 (2014)]; (ii) in performing this expansion, we also obtain, for the first time, the explicit 3.5PN leading-order tail-induced spin-spin flux term; and (iii) pushing the PN expansion of the (nonspinning) EOB flux up to 5.5PN order, we compute 4PN, 5PN, and 5.5PN contributions to the energy flux, though in a form that explicitly depends on, currently unknown, 4PN and 5PN non-test-mass corrections to the factorized waveform amplitudes. Within this (parametrized) 4.5PN accuracy, we calculate the Taylor F2 approximant. Focusing for simplicity on the nonspinning case and using the numerical-relativity calibrated IMRPhenomD waveform model as a benchmark, we demonstrate that it is possible to reproduce the derivative of the IMRPhenomD phase (say up to the frequency of the Schwarzschild last-stable-orbit) by flexing only a 4PN “effective” waveform amplitude parameter. A preliminary analysis also illustrates that similar results can be obtained for the spin-aligned case provided only the leading-order spin-orbit and spin-spin terms are kept. Our findings suggest that these types of EOB-derived, parametrized, higher-order, PN approximants may serve as promising tools to construct inspiral-merger-ringdown phenomenological models or even to replace the standardly used 3.5PN-accurate TaylorF2 approximant in searches of small-mass binaries.

We study the consequences of reheating in quintessential inflation. From simple inflationary quintessential models introduced by de Haro, Amorós, and Pan in [Phys. Rev. D 93, 084018 (2016)] and [Phys. Rev. D 94, 064060 (2016)], we show that when the reheating is due to the production of heavy massive particles conformally coupled with gravity, a viable model which matches with the current observational data is only possible for reheating temperatures that range between 1 GeV and $10^4\mathrm{GeV}$. On the other hand, when the Universe reheats via the production of massless particles, viability of the model is only possible when those particles are nearly conformally coupled with gravity, leading to a reheating temperature between 1 MeV and $10^4\mathrm{GeV}$.

We study the production of high energy neutrinos in jets from the tidal disruption of stars by supermassive black holes. The diffuse neutrino flux expected from these tidal disruption events (TDEs) is calculated both analytically and numerically, taking into account the dependence of the rate of TDEs on the redshift and black hole mass. We find that $\sim 10\%$ of the observed diffuse flux at IceCube at an energy of about 1 PeV can come from TDEs if the characteristics of known jetted tidal disruption events are assumed to apply to the whole population of these sources. If, however, plausible scalings of the jet Lorentz factor or variability time scale with the black hole mass are taken into account, the contribution of the lowest mass black holes to the neutrino flux is enhanced. In this case, TDEs can account for most of the neutrino flux detected at IceCube, describing both the neutrino flux normalization and spectral shape with moderate baryonic loadings. While the uncertainties on our assumptions are large, a possible signature of TDEs as the origin of the IceCube signal is the transition of the flux flavor composition from a pion beam to a muon damped source at the highest energies, which will also result in a suppression of Glashow resonance events.

We consider a scenario where time dependence on physical parameters is introduced by the misalignment of an ultralight scalar field. The initial vacuum expectation value of such field at the early time remains a constant until Hubble becomes comparable to its mass. Interesting cosmological consequences are considered. Light sterile neutrinos hinted by terrestrial neutrino experiments are studied as a benchmark model. We show the big-bang nucleosynthesis constraints can be easily avoided in this scenario, even if reheating temperature is high. The scalar can be naturally light in spite of its couplings to other fields. Parameters of sterile neutrino may remain changing with time nowadays. This can further relax the tension from the recent IceCube constraints.

We point out that in the minimal left-right realization of TeV scale seesaw for neutrino masses, the neutral scalar from the right-handed $SU(2{)}_R$ breaking sector could be much lighter than the right-handed scale. We discuss for the first time the constraints on this particle from low-energy flavor observables and find that the light scalar is necessarily long-lived. We show that it can be searched for at the LHC via displaced signals of a collimated photon jet and can also be tested in current and future high-intensity experiments. In contrast to the unique diphoton signal (and associated jets) in the left-right case, a generic beyond-standard-model light scalar decays mostly to leptons or jets. Thus, the diphoton channel proposed here provides a new avenue to test the left-right framework and reveal the underlying neutrino mass generation mechanism.

Multiplicity distributions of charged particles produced in the $e^{+}{e}^{-}$ collisions at energies ranging from 14 to 91 GeV are studied using Tsallis $q$-statistics and the recently proposed Weibull distribution functions, in both restricted rapidity windows as well as in full phase space. It is shown that Tsallis $q$-statistics explains the data in a statistically acceptable manner in all rapidity ranges while the Weibull distribution fails to reproduce the data in full phase space. Modifications to the distributions are proposed to establish manifold improvements in the fitting of the data.

We construct the electromagnetic anomaly effective term for a generalized linear sigma model with two chiral nonets, one with a quark-antiquark structure, the other one with a four-quark content. We compute in the leading order of this framework the decays into two photons of six pseudoscalars: ${\pi }_0(137)$, ${\pi }_0(1300)$, $\eta (547)$, $\eta (958)$, $\eta (1295)$ and $\eta (1760)$. Our results agree well with the available experimental data.

We describe a novel, very fast and robust, directed search incoherent method (which means that the phase information is lost) for periodic gravitational waves from neutron stars in binary systems. As a directed search, we assume the source sky position to be known with enough accuracy, but all other parameters (including orbital ones) are supposed to be unknown. We exploit the frequency modulation due to source orbital motion to unveil the signal signature by commencing from a collection of time and frequency peaks (the so-called “peakmap”). We validate our algorithm (pipeline), adding 131 artificial continuous-wave signals from pulsars in binary systems to simulated detector Gaussian noise, characterized by a power spectral density $S_h=4\times {10}^{-24}{\mathrm{Hz}}^{-1/2}$ in the frequency interval [70, 200] Hz, which is overall commensurate with the advanced detector design sensitivities. The pipeline detected 128 signals, and the weakest signal injected (added) and detected has a gravitational-wave strain amplitude of $\sim {10}^{-24}$, assuming one month of gapless data collected by a single advanced detector. We also provide sensitivity estimations, which show that, for a single-detector data covering one month of observation time, depending on the source orbital Doppler modulation, we can detect signals with an amplitude of $\sim 7\times {10}^{-25}$. By using three detectors, and one year of data, we would easily gain a factor 3 in sensitivity, translating into being able to detect weaker signals. We also discuss the parameter estimate proficiency of our method, as well as computational budget: sifting one month of single-detector data and 131 Hz-wide frequency range takes roughly 2.4 CPU hours. Hence, the current procedure can be readily applied in ally-sky schemes, sieving in parallel as many sky positions as permitted by the available computational power. Finally, we introduce (ongoing and future) approaches to attain sensitivity improvements and better accuracy on parameter estimates in view of the use on real advanced detector data.

We use the Iyer-Wald formalism to derive an extended first law of entanglement that includes variations in the cosmological constant, Newton’s constant and—in the case of higher-derivative theories—all the additional couplings of the theory. In Einstein gravity, where the number of degrees of freedom $N^2$ of the dual field theory is a function of $\mathrm{\Lambda }$ and $G$, our approach allows us to vary $N$ by keeping the field theory scale fixed or to vary the field theory scale by keeping $N$ fixed. We also derive an extended first law of entanglement for Gauss-Bonnet and Lovelock gravity and show that in these cases all the extra variations reorganize nicely in terms of the central charges of the theory. Finally, we comment on the implications for renormalization group flows and $c$-theorems in higher dimensions.

We consider a massive gravity black hole in four-dimensional anti–de Sitter space and study the effect of thermal fluctuations on the thermodynamics of the black hole. We consider thermal fluctuations as logarithmic correction terms in the entropy. We analyze the effect of logarithmic correction on thermodynamics potentials like Helmholtz and Gibbs which are found decreasing functions. We study critical points and stability and find that the presence of logarithmic correction is necessary to have stable phase and critical point.

When a spacetime has boundaries, the entangling surface does not have to be necessarily compact and it may have boundaries as well. Then there appear a new, boundary, contribution to the entanglement entropy due to the intersection of the entangling surface with the boundary of the spacetime. We study the boundary contribution to the logarithmic term in the entanglement entropy in dimensions $d=3$ and $d=4$ when the entangling surface is orthogonal to the boundary. In particular, we compute a boundary term in the entropy of $\mathcal{N}=4$ supergauge multiplet at weak coupling. For gauge fields we use a prescription which is consistent with the positive area law. The boundary term is compared with the holographic calculation of the entropy based on the Ryu-Takayanagi proposal adapted appropriately to the present situation. We find a complete agreement between these two calculations provided the boundary conditions imposed on the gauge multiplet preserve $1/2$ of the supersymmetry and the extension of the boundary into the anti–de Sitter bulk is a minimal hypersurface.

We investigate the behavior of shear viscosity in the presence of small anisotropy and a finite chemical potential. First, we construct an anisotropic Reissner Nordström black brane in five dimensions in a simple Einstein-Maxwell theory with a small linear dilaton. This solution is characterized by three mass scales: anisotropy $\rho$, temperature $T$, and chemical potential $\mu$. We find this solution up to second order in the dilaton anisotropy parameter $\rho$. This black brane solution corresponds to an anisotropic phase where the anisotropy is small compared to the temperature and chemical potential. We find that in this anisotropic phase, some components of the anisotropic shear viscosity tensor, which are spin one with respect to the residual symmetry after breaking rotational invariance, violates the KSS bound ($\frac{\eta }{s}\ge \frac{1}{4\pi }$) proposed by Kovtun, Son, and Starinets. We identify the regions of the parameter space where these violations are significant. We carry out a similar analysis in four dimensions and find a similar violation of the KSS bound for the spin one components to demonstrate the generality of the result. Our results are particularly relevant in the context of strongly coupled systems found in nature. We also provide an intuitive understanding of the results using dimensional reduction and a Boltzmann calculation in a weakly coupled version of a similar system. The Boltzmann analysis performed in a system of weakly interacting particles in a linear potential also shows that components of the viscosity tensor may be reduced. It is intriguing that the Boltzmann analysis also predicts the corrections to be negative and that too in a manner similar to the anisotropic strongly coupled theories with smooth gravity duals.