In this paper we construct asymptotically locally AdS and flat black holes in the presence of a scalar field whose kinetic term is constructed out from a linear combination of the metric and the Einstein tensor. The field equations as well as the energy-momentum tensor are second order in the metric and the field, therefore the theory belongs to the ones defined by Horndeski. We show that in the presence of a cosmological term in the action, it is possible to have a real scalar field in the region outside the event horizon. The solutions are characterized by a single integration constant, the scalar field vanishes at the horizon and it contributes to the effective cosmological constant at infinity. We extend these results to the topological case. The solution is disconnected from the maximally symmetric AdS background, however, within this family there exists a gravitational soliton which is everywhere regular. This soliton is therefore used as a background to define a finite Euclidean action and to obtain the thermodynamics of the black holes. For a certain region in the space of parameters, the thermodynamic analysis reveals a critical temperature at which a Hawking-Page phase transition between the black hole and the soliton occurs. We extend the solution to arbitrary dimensions greater than 4 and show that the presence of a cosmological term in the action allows one to consider the case in which the standard kinetic term for the scalar it is not present. In such a scenario, the solution reduces to an asymptotically flat black hole.

A class of perturbatively charged rotating dilaton black hole solutions coupled to the nonlinear Born-Infeld electrodynamics is presented. The strategy for obtaining these solutions is to start from Myers-Perry solutions and then, considering the effects of the dilaton field, Born-Infeld parameter as well as the electric charge as a perturbative parameter. We perform the perturbations up to fourth order in the extremal black holes of Einstein-Born-Infeld-dilaton gravity with two equal angular momenta and arbitrary dilaton coupling constant. We discuss the physical properties of these black holes and study their dependence on the perturbative parameter $q$, the dilaton coupling constant $\alpha$, and the Born-Infeld parameter $\beta$. One can see these black holes solutions satisfy a generalized Smarr relation.

We construct electrically charged $Q$-balls and boson stars in a model with a scalar self-interaction potential resulting from gauge mediated supersymmetry breaking. We discuss the properties of these solutions in detail and emphasize the differences to the uncharged case. We observe that $Q$-balls can only be constructed up to a maximal value of the charge of the scalar field, while for boson stars the interplay between the attractive gravitational force and the repulsive electromagnetic force determines their behavior. We find that the vacuum is stable with respect to pair production in the presence of our charged boson stars. We also study the motion of charged, massive test particles in the space-time of boson stars. We find that in contrast to charged black holes the motion of charged test particles in charged boson star space-times is planar, but that the presence of the scalar field plays a crucial role for the qualitative features of the trajectories. Applications of this test particle motion can be made in the study of extreme-mass ratio inspirals as well as astrophysical plasmas relevant e.g. in the formation of accretion discs and polar jets of compact objects.

Here we investigate the cosmic dynamics of Friedmann-Robertson-Walker universes—flat spatial sections—which are driven by nonlinear electrodynamics (NLED) Lagrangians. We pay special attention to check the sign of the square sound speed since, whenever the latter quantity is negative, the corresponding cosmological model is classically unstable against small perturbations of the background energy density. Besides, based on causality arguments, one has to require that the mentioned small perturbations of the background should propagate at most at the local speed of light. We also look for the occurrence of curvature singularities. Our results indicate that several cosmological models which are based in known NLED Lagrangians, either are plagued by curvature singularities of the sudden and/or big rip type, or are violently unstable against small perturbations of the cosmological background—due to the negative sign of the square sound speed—or both. In addition, causality issues associated with superluminal propagation of the background perturbations may also arise.

Inflation can be parametrized by means of truncated flow equations. In this “horizon-flow” setup, generic results have been obtained, such as typical values for $r/(1-n_{\mathrm{S}})$. They are sometimes referred to as intrinsic features of inflation itself. In this paper we first show that the phenomenological class of inflationary potentials sampled by horizon flow is directly responsible for such predictions. They are therefore anything but generic. Furthermore, the horizon-flow setup is shown to rely on trajectories in phase space that differ from the slow roll. For a given potential, we demonstrate that this renders horizon flow blind to entire relevant inflationary regimes, for which the horizon-flow trajectory is shown to be unstable. This makes horizon flow a biased parametrization of inflation.

Using the QCD sum rules approach, we study the mass and the decay widths of the $Y(3940)$ state, assuming that it can be described by a mixed charmonium-molecule scalar state, i.e., a mixture between the ${\chi }_{c0}$ charmonium and $D^{*}{\overline{D}}^{*}$ molecule. Using a current with $J^{PC}=0^{++}$, we estimate for the mixing angle, $\theta =(76.0\pm 5.0)°$, resulting in a mass value of $M_Y=(3.95\pm 0.11)\mathrm{GeV}$, which is in reasonable agreement with the experimental mass of the $Y(3940)$ state. For the decay width, we evaluate the channels $Y\to J/\psi \omega$ and $Y\to \gamma \gamma$. We find the values ${\mathrm{\Gamma }}_{Y\to J/\psi \omega }\approx (1.7\pm 0.6)\mathrm{MeV}$ and ${\mathrm{\Gamma }}_{Y\to \gamma \gamma }\approx (1.6\pm 1.3)\mathrm{KeV}$, respectively. We also study the decay process of this state into channels containing $D\overline{D}$ mesons in the final state. The result for the order of magnitude of the product ${\mathrm{\Gamma }}_{Y\to \gamma \gamma }\times {\mathrm{\Gamma }}_{Y\to J/\psi \omega }\sim \mathcal{O}(10^3){\mathrm{KeV}}^2$ is also in reasonable agreement with the experimental data. We thus conclude that the present description of the $Y(3940)$ as a mixed charmonium-molecule state is a possible scenario to explain the structure of such a state.

In this paper, we extend the well-known QCD sum rules used in the calculation of the mass of heavy mesons to estimate the modification of the charged $B$-meson mass, $m_B$, in the presence of an external Abelian magnetic field, $eB$. Two simplifying limits were considered: the weak field limit, in which the external field satisfies $eB\ll m^2$ (with $m$ being any of the masses involved); and the strong field limit, in which the field strength is small in comparison to the bottom quark mass (or the $B$-meson mass) squared, but it is large compared to the mass of the light quarks, i.e., $m_{u,d}^2\ll eB\ll m_{b,B}^2$. We found that $m_B$ decreases with the magnetic field in both of these limits.

The interquark potential in charmonium states is calculated in both the zero and nonzero temperature phases from a first-principles lattice QCD calculation. Simulations with two dynamical quark flavors are used with temperatures $T$ in the range $0.4T_c\lesssim T\lesssim 1.7T_c$, where $T_c$ is the deconfining temperature. The correlators of point-split operators are analyzed to gain spatial information about the charmonium states. A method introduced by the HAL QCD Collaboration and based on the Schrödinger equation is applied to obtain the interquark potential. We find a clear temperature dependence with the central potential agreeing with the Cornell potential in the confined phase and becoming flatter (more screened) as the temperature increases past the deconfining temperature. This is the first time the interquark potential has been calculated for realistic quarks at finite temperature.

We present a static, spherically symmetric, traversable wormhole solution to multimetric gravity which is sustained by only nonexotic matter, i.e., matter which satisfies all energy conditions. The possibility of this solution arises from the fact that under certain conditions the multimetric gravitational field equations reduce to the Einstein equations, but with a negative effective gravitational constant. We show that the Arnowitt-Deser-Misner mass of this wormhole vanishes, so that it appears massless to observers in the asymptotically flat spacetime. We finally speculate on the feasibility of creating and maintaining this type of wormhole by an advanced civilization.

In a recently proposed Higgs-seesaw model the observed scale of dark energy results from a metastable false vacuum energy associated with mixing of the standard model Higgs particle and a scalar associated with new physics at the scale of unification or the Planck scale. Here we address the issue of how to ensure metastability of this state over cosmological time. We consider new tree-level operators, the presence of a thermal bath of hidden sector particles, and quantum corrections to the effective potential. We find that in the thermal scenario many additional light degrees of freedom are typically required unless coupling constants are somewhat fine-tuned. However quantum corrections arising from as few as one additional light scalar field can provide the requisite support. We also briefly consider implications of late-time vacuum decay for the perdurance of observed structures in the universe in this model.

Skyrmions of different dimensions are related by domain walls. We obtain explicit full numerical solutions of various Skyrmion configurations trapped inside a domain wall. We find for the quadratic mass term that multi-Skyrmions are ring shaped and conjecture for the linear mass term, that the lowest-energy state of multi-Skyrmions will consist of charge-2 rings accommodated in a lattice.

We introduce a system composed of two ($2+1$)-dimensional baby-Skyrmion models (BSMs) set on parallel planes and linearly coupled by tunneling of fields. This system can be realized in a dual-layer ferromagnetic medium. Unlike dual-core models previously studied in nonlinear optics and Bose-Einstein condensates, here the symmetry-breaking bifurcation (SBB) in solitons (baby Skyrmions) occurs with the increase of the intercore coupling ($\kappa$), rather than with its decrease, due to the fact that, even in the uncoupled system, neither core may be empty. Prior to the onset of the symmetry breaking between the two components of the solitons, they gradually separate in the opposite directions, due to the increase of $\kappa$, which is explained in an analytical form by means of an effective interaction potential. Such evolution scenarios are produced for originally symmetric states with topological charges in the two cores, $B^{(1)}=B^{(2)}=1$, 2, 3, 4. The evolution of mixed states, of the $(B^{(1)},B^{(2)})=(1,2)$ and (2,4) types, with the variation of $\kappa$ is studied too.

We use an effective matrix model to study deconfinement in a pure $SU(N_c)$ gauge theory, without quarks, in $d=2+1$ dimensions. Expanding about a constant background ${\mathcal{A}}_0$ field, we construct an effective potential for the eigenvalues of the thermal Wilson line for general $N_c$ and in the large-$N_c$ limit. The numerical results are presented using one, two, and four free parameters, which are determined by fitting directly to the lattice data for the pressure. The matrix model shows a good agreement with numerical lattice simulations for the pressure and the interaction measure, starting from the perturbative limit up to the critical temperature. For the pressure, the details of ${\mathcal{A}}_0$-dependent nonperturbative terms are relevant only in a narrow transition region below $\sim 1.2T_d$. This is also the range where the Polyakov loop deviates notably from one. In accordance with the lattice results we find that, up to a trivial factor ${N_c}^2-1$, there is only a mild dependence on the number of colors.

We present the results of the search for an astrophysical gravitational-wave stochastic background during the second Einstein Telescope mock data and science challenge. Assuming that the loudest sources can be detected individually and removed from the data, we show that the residual background can be recovered with an accuracy of 1% with the standard cross-correlation statistic, after correction of a systematic bias due to the anisotropy of the sources.

Adopting our new method for matching general relativistic, ideal magnetohydrodynamics to its force-free limit, we perform the first systematic simulations of force-free pulsar magnetospheres in general relativity. We endow the neutron star with a general relativistic dipole magnetic field, model the interior with ideal magnetohydrodynamics, and adopt force-free electrodynamics in the exterior. Comparing the spin-down luminosity to its corresponding Minkowski value, we find that general relativistic effects give rise to a modest enhancement: the maximum enhancement for $n=1$ polytropes is $\sim 23\%$. Evolving a rapidly rotating $n=0.5$ polytrope we find an even greater enhancement of $\sim 35\%$. Using our simulation data, we derive fitting formulas for the pulsar spin-down luminosity as a function of the neutron star compaction, angular speed, and dipole magnetic moment. We expect stiffer equations of state and more rapidly spinning neutron stars to lead to even larger enhancements in the spin-down luminosity.

We describe a UV complete asymptotically fragile Lorentz-invariant theory exhibiting superluminal signal propagation. Its low energy effective action contains “wrong” sign higher dimensional operators. Nevertheless, the theory gives rise to an $S$ matrix, which is defined at all energies. As expected for a nonlocal theory, the corresponding scattering amplitudes are not exponentially bounded on the physical sheet, but otherwise are healthy. We study some of the physical consequences of this $S$ matrix.

In this paper we report on what we believe is the first successful implementation of relativistic hydrodynamics, coupled to dynamical spacetimes, in spherical polar coordinates without symmetry assumptions. We employ a high-resolution shock-capturing scheme, which requires that the equations be cast in a flux-conservative form. One example of such a form is the “Valencia” formulation, which has been adopted in numerous applications, in particular in Cartesian coordinates. Here we generalize this formulation to allow for a reference-metric approach, which provides a natural framework for calculations in curvilinear coordinates. In spherical polar coordinates, for example, it allows for an analytical treatment of the singular $r$ and $\sin \theta$ terms that appear in the equations. We experiment with different versions of our generalized Valencia formulation in numerical implementations of relativistic hydrodynamics for both fixed and dynamical spacetimes. We consider a number of different tests—nonrotating and rotating relativistic stars, as well as gravitational collapse to a black hole—to demonstrate that our formulation provides a promising approach to performing fully relativistic astrophysics simulations in spherical polar coordinates.

We perform a fully relativistic analysis of even-parity linear perturbations around a static and spherically symmetric solution in the most general scalar-tensor theory with second-order field equations. This paper is a sequel to Kobayashi et al. [Phys. Rev. D 85, 084025 (2012)], in which the linear perturbation analysis for the odd-parity modes is presented. Expanding the Horndeski action to second order in perturbations and eliminating auxiliary variables, we derive the quadratic action for even-parity perturbations written solely in terms of two dynamical variables. The two perturbations can be interpreted as the gravitational and scalar waves. Correspondingly, we obtain two conditions to evade ghosts and two conditions for the absence of gradient instabilities. Only one in each pair of conditions yields a new stability criterion, as the conditions derived from the stability of the gravitational-wave degree of freedom coincide with those in the odd-parity sector. Similarly, the propagation speed of one of the two modes is the same as that for the odd-parity mode, while the other differs in general from them. Our result is applicable to all the theories of gravitation with an extra single scalar degree of freedom such as the Brans-Dicke theory, $f(R)$ models, and Galileon gravity.

We construct a fully analytic, general relativistic, nonspinning black hole binary spacetime that approximately solves the vacuum Einstein equations everywhere in space and time for black holes sufficiently well separated. The metric is constructed by asymptotically matching perturbed Schwarzschild metrics near each black hole to a two-body post-Newtonian metric far from them and a two-body post-Minkowskian metric farther still. Asymptotic matching is done without linearizing about a particular time slice, and thus it is valid dynamically and for all times, provided the binary is sufficiently well separated. This approximate global metric can be used for long dynamical evolutions of relativistic magnetohydrodynamical, circumbinary disks around inspiraling supermassive black holes to study a variety of phenomena.

We explore the observational implications of models of intermediate inflation driven by modified dispersion relations, specifically those representing the phenomenon of dimensional reduction in the ultraviolet limit. These models are distinct from the standard ones because they do not require violations of the strong energy condition, and this is reflected in their structure formation properties. We find that they can naturally accommodate deviations from exact scale invariance. They also make clear predictions for the running of the spectral index and tensor modes, rendering the models straightforwardly falsifiable. We discuss the observational prospects for these models and the implications these may have for quantum gravity scenarios.