We study spectral and thermodynamic properties of the Sachdev-Ye-Kitaev model, a variant of the $k$-body embedded random ensembles studied for several decades in the context of nuclear physics and quantum chaos. We show analytically that the fourth- and sixth-order energy cumulants vanish in the limit of a large number of particles $N\to \infty$, which is consistent with a Gaussian spectral density. However, for finite $N$, the tail of the average spectral density is well approximated by a semicircle law. The specific heat coefficient, determined numerically from the low-temperature behavior of the partition function, is consistent with the value obtained by previous analytical calculations. For energy scales of the order of the mean level spacing we show that level statistics are well described by random matrix theory. Due to the underlying Clifford algebra of the model, the universality class of the spectral correlations depends on $N$. For larger energy separations we identify an energy scale that grows with $N$, reminiscent of the Thouless energy in mesoscopic physics, where deviations from random matrix theory are observed. Our results are a further confirmation that the Sachdev-Ye-Kitaev model is quantum chaotic for all time scales. According to recent claims in the literature, this is an expected feature in field theories with a gravity dual.

Is the evaporation of a black hole described by a unitary theory? In order to shed light on this question—especially aspects of this question such as a black hole’s negative specific heat—we consider the real-time dynamics of a solitonic object in matrix quantum mechanics, which can be interpreted as a black hole (black zero-brane) via holography. We point out that the chaotic nature of the system combined with the flat directions of its potential naturally leads to the emission of D0-branes from the black brane, which is suppressed in the large $N$ limit. Simple arguments show that the black zero-brane, like the Schwarzschild black hole, has negative specific heat, in the sense that the temperature goes up when it evaporates by emitting D0-branes. While the largest Lyapunov exponent grows during the evaporation, the Kolmogorov-Sinai entropy decreases. These are consequences of the generic properties of matrix models and gauge theory. Based on these results, we give a possible geometric interpretation of the eigenvalue distribution of matrices in terms of gravity. Applying the same argument in the M-theory parameter region, we provide a scenario to derive the Hawking radiation of massless particles from the Schwarzschild black hole. Finally, we suggest that by adding a fraction of the quantum effects to the classical theory, we can obtain a matrix model whose classical time evolution mimics the entire life of the black brane, from its formation to the evaporation.

We consider the existence and stability of solitons in generalized Galileons, scalar-field theories with higher-derivative interactions but second-order equations of motion. It has previously been proven that no stable, static solitons exist in a single Galileon theory using an argument invoking the existence of zero modes for the perturbations. Here we analyze the applicability of this argument to generalized Galileons and discuss how this may be avoided by having potential terms in the energy functional for the perturbations or by including time dependence. Given the presence of potential terms in the Lagrangian for the perturbations, we find that stable, static solitons are not ruled out in conformal and (anti–)de Sitter Galileons. For the case of Dirac-Born-Infeld and conformal Galileons, we find that solitonic solutions moving at the speed of light exist, the former being stable and the latter unstable if the background soliton satisfies a certain condition.

The explicit expressions for the high-temperature expansions of the one-loop corrections to the thermodynamic potential coming from charged scalar and Dirac particles and, separately, from antiparticles in a constant homogeneous magnetic field are derived. The explicit expressions for the nonperturbative corrections to the effective action at finite temperature and density are obtained. Thermodynamic properties of a gas of charged scalars in a constant homogeneous magnetic field are analyzed in the one-loop approximation. It turns out that, in this approximation, the system suffers a first-order phase transition from the diamagnetic to the superconducting state at sufficiently high densities. The improvement of the one-loop result by summing the ring diagrams is investigated. This improvement leads to a drastic change in thermodynamic properties of the system. The gas of charged scalars passes to the ferromagnetic state rather than the superconducting one at high densities and sufficiently low temperatures, in the high-temperature regime.

Following a successfully quantization scheme previously developed in Ref. [R. Casana, M. M. Ferreira, Jr., and F. E. P. dos Santos, Phys. Rev. D 90, 105025 (2014).] for a parity-even gauge sector of the SME, we have established the Gupta-Bleuler quantization of a parity-odd and $CPT$-even electrodynamics of the standard model extension (SME) without the need for a small photon mass regulator. Keeping the photons massless, we have adopted the gauge-fixing condition: $G(A_{\mu })=({\partial }_0+{\kappa }^{0j}{\partial }_j)(A_0+{\kappa }^{0k}{A}_k)+{\partial }_i{A}^i$. The four polarization vectors of the gauge field are exactly determined by solving an eigenvalue problem, exhibiting birefringent second-order contributions in the Lorentz-violating parameters. They allow us to express the Hamiltonian in terms of annihilation and creation operators whose positivity is guaranteed by imposing a weak Gupta-Bleuler constraint, defining the physical states. Consequently, we compute the field commutation relation that has been expressed in terms of Pauli-Jordan functions modified by Lorentz violation whose light-cone structures have allowed us to analyze the microcausality issue.

Recently, a fully covariant version of the theory of $F(T)$ torsion gravity has been introduced by M. Kršśák and E. Saridakis [Classical Quantum Gravity 33, 115009 (2016)]. In covariant $F(T)$ gravity, the Schwarzschild solution is not a vacuum solution for $F(T)\ne T$, and therefore determining the spherically symmetric vacuum is an important open problem. Within the covariant framework, we perturbatively solve the spherically symmetric vacuum gravitational equations around the Schwarzschild solution for the scenario with $F(T)=T+(\alpha /2)T^2$, representing the dominant terms in theories governed by Lagrangians analytic in the torsion scalar. From this, we compute the perihelion shift correction to solar system planetary orbits as well as perturbative gravitational effects near neutron stars. This allows us to set an upper bound on the magnitude of the coupling constant, $\alpha$, which governs deviations from general relativity. We find the bound on this nonlinear torsion coupling constant by specifically considering the uncertainty in the perihelion shift of Mercury. We also analyze a bound from a similar comparison with the periastron orbit of the binary pulsar PSR J0045-7319 as an independent check for consistency. Setting bounds on the dominant nonlinear coupling is important in determining if other effects in the Solar System or greater universe could be attributable to nonlinear torsion.

The mass parameters of compact objects such as boson stars, Schwarzschild, Reissner-Nordström, and Kerr black holes are computed in terms of the measurable redshift-blueshift ($z_{\mathrm{red}}$, $z_{\mathrm{blue}}$) of photons emitted by particles moving along circular geodesics around these objects and the radius of their orbits. We find bounds for the values of ($z_{\mathrm{red}}$, $z_{\mathrm{blue}}$) that may be observed. For the case of the Kerr black hole, recent observational estimates of Sgr $A^{*}$ mass and rotation parameter are employed to determine the corresponding values of these red-blue shifts.

We study the effective field theory that describes the low-energy physics of self-gravitating media. The field content consists of four derivatively coupled scalar fields that can be identified with the internal comoving coordinates of the medium. Imposing SO(3) internal spatial invariance, the theory describes supersolids. Stronger symmetry requirements lead to superfluids, solids and perfect fluids, at lowest order in derivatives. In the unitary gauge, massive gravity emerges, being thus the result of a continuous medium propagating in spacetime. Our results can be used to explore systematically the effects and signatures of modifying gravity consistently at large distances. The dark sector is then described as a self-gravitating medium with dynamical and thermodynamic properties dictated by internal symmetries. These results indicate that the divide between dark energy and modified gravity, at large distance scales, is simply a gauge choice.

We develop the model proposed by Cortês, Gomes and Smolin [1] to predict cosmological signatures of time-asymmetric extensions of general relativity. Within this class of models the equation of motion of chiral fermions is modified by a torsion term. This term leads to a dispersion law for neutrinos that associates a new time-varying energy with each particle. We find a new neutrino contribution to the Friedmann equation resulting from the torsion term in the Ashtekar connection. In this paper we explore the phenomenology of this term and observational consequences for cosmological evolution. We show that constraints on the critical energy density will ordinarily render this term unobservably small, a maximum of order ${10}^{-25}$ of the neutrino energy density today. However, if the time-asymmetric dark energy is tuned to cancel the cosmological constant, the torsion effect may be a dark matter candidate.

In Gleyzes-Langlois-Piazza-Vernizzi (GLPV) scalar-tensor theories, which are outside the domain of second-order Horndeski theories, it is known that there exists a solid angle deficit singularity in the case where the parameter ${\alpha }_{\mathrm{H}}$ characterizing the deviation from Horndeski theories approaches a nonvanishing constant at the center of a spherically symmetric body. Meanwhile, it was recently shown that second-order generalized Proca theories with a massive vector field $A^{\mu }$ can be consistently extended to beyond-generalized Proca theories, which recover shift-symmetric GLPV theories in the scalar limit $A^{\mu }\to {\nabla }^{\mu }\chi$. In beyond-generalized Proca theories up to quartic-order Lagrangians, we show that solid angle deficit singularities are generally absent due to the existence of a temporal vector component. We also derive the vector-field profiles around a compact object and show that the success of the Vainshtein mechanism operated by vector Galileons is not prevented by new interactions in beyond generalized Proca theories.

We examine updated prospects for detecting WIMPs in supersymmetric models via direct and indirect dark matter search experiments. We examine several historical and also still viable scenarios: projections for well-tempered neutralinos (WTN), projections from the MasterCode (MC), BayesFits (BF) and Fittino (FO) collaborations, nonthermal wino dark matter (NThW) and finally mixed axion-Higgsino dark matter from SUSY with radiatively driven naturalness (RNS). The WTN is ruled out by recent limits from XENON and LUX collaborations. The NThW scenario, previously on tenuous ground due to gamma-line searches, appears also ruled out by recent combined Fermi-LAT/MAGIC limits combined with new HESS results from continuum gamma rays. Substantial portions of MC parameter space and 1 TeV Higgsino parameter space from BF group are ruled out. The 100–300 GeV Higgsino-like WIMP from RNS survives due to its possible depleted local abundance (where the axion may make up the bulk of dark matter). Projections from ton-scale noble liquid detectors should discover or rule out WIMPs from the remaining parameter space of these surviving models.

A comprehensive study on the nature of the $Z_c(3900)$ resonant structure is carried out in this work. By constructing the pertinent effective Lagrangians and considering the important final-state-interaction effects, we first give a unified description to all the relevant experimental data available, including the $J/\psi \pi$ and $\pi \pi$ invariant mass distributions from the $e^{+}{e}^{-}\to J/\psi \pi \pi$ process, the $h_c\pi$ distribution from $e^{+}{e}^{-}\to h_c\pi \pi$, and also the $D{\overline{D}}^{*}$ spectrum in the $e^{+}{e}^{-}\to D{\overline{D}}^{*}\pi$ process. After fitting the unknown parameters to the previous data, we search the pole in the complex energy plane and find only one pole in the nearby energy region in different Riemann sheets. Therefore, we conclude that $Z_c(3900)$ is of $D{\overline{D}}^{*}$ molecular nature, according to the pole counting rule method [Nucl. Phys. A543, 632 (1992); Phys. Rev. D 35, 1633 (1987)]. We emphasize that the conclusion based upon the pole counting method is not trivial, since both the $D{\overline{D}}^{*}$ contact interactions and the explicit $Z_c$ exchanges are introduced in our analyses and they lead to the same conclusion.

The LHCb Collaboration has recently observed four $J/\psi \varphi$ structures called $X(4140)$, $X(4274)$, $X(4500)$, and $X(4700)$ in the $B^{+}\to J/\psi \varphi K^{+}$ decays. We study them herein using a nonrelativistic constituent quark model in which the degrees of freedom are quark-antiquark and meson-meson components. The $X(4140)$ resonance appears as a cusp in the $J/\psi \varphi$ channel due to the near coincidence of the $D_s^{\pm }{D}_s^{*\pm }$ and $J/\psi \varphi$ mass thresholds. The remaining three [$X(4274)$, $X(4500)$, and $X(4700)$] appear as conventional charmonium states with quantum numbers $3{{}^{3}P}_1$, $4{{}^{3}P}_0$, and $5{{}^{3}P}_0$, respectively, and their masses and widths are slightly modified due to their coupling with the corresponding closest meson-meson thresholds. A particular feature of our quark model is a lattice-based screened linear confining interaction that has been constrained in the light-quark sector and usually produces higher excited heavy-quark states with lower masses than standard quark model predictions.

We evaluate the elliptic gluon generalized transverse-momentum-dependent distribution inside a large nucleus using the McLerran-Venugopalan model. We further show that this gluon distribution can be probed through the angular correlation in virtual photon quasielastic scattering on a nucleus.

We study the $D$-wave charmed baryons of $SU(3)$ flavor ${\overline{\mathbf{3}}}_F$ using the method of QCD sum rules in the framework of heavy quark effective theory. We find that the ${\mathrm{\Lambda }}_c(2880)$, ${\mathrm{\Xi }}_c(3055)$, and ${\mathrm{\Xi }}_c(3080)$ can be well described by the $D$-wave $SU(3)$ ${\overline{\mathbf{3}}}_F$ charmed baryon multiplets of $J^P=3/2^{+}$ and $5/2^{+}$, which contain two $\lambda$-mode orbital excitations; i.e., the ${\mathrm{\Lambda }}_c(2880)$ has $J^P=5/2^{+}$, and the ${\mathrm{\Xi }}_c(3055)$ and ${\mathrm{\Xi }}_c(3080)$ have $J^P=3/2^{+}$ and $5/2^{+}$, respectively. Our results also suggest that the ${\mathrm{\Lambda }}_c(2880)$ has a partner state, the ${\mathrm{\Lambda }}_c(3/2^{+})$ of $J^P=3/2^{+}$. Its mass is around $2.81_{-0.18}^{+0.33}\mathrm{GeV}$, and the mass difference between it and the ${\mathrm{\Lambda }}_c(2880)$ is $28_{-24}^{+45}\mathrm{MeV}$. We also evaluate the masses of their bottom partners.

Early Universe cosmology imposes stringent bounds on light sterile neutrinos mixing with the active flavors. Here we discuss how altered dispersion relations can weaken such bounds and allow compatibility of new sterile neutrino degrees of freedom with early Universe cosmology and particular a successful generation of the light elements in the early Universe.

We present a detailed phenomenological study of $W$-boson production in association with a jet through next-to-next-to-leading order (NNLO) in perturbative QCD. Fiducial cross sections and differential distributions for both 8 TeV and 13 TeV LHC collisions are presented, as are results for both the inclusive one-jet bin and the exclusive one-jet bin. Two different event selection criteria are considered: a general selection with standard cuts used in experimental analyses, and a boosted selection that focuses on high transverse momentum jets. We discuss the higher-order corrections in detail and identify for which observables and phase space regions the QCD perturbative expansion is under good theoretical control, and where additional work is needed. For most distributions and phase space regions the QCD perturbative expansion exhibits good convergence after the inclusion of the NNLO corrections.

A special purpose solver, based on the Magnus expansion, well suited for the integration of the linear three neutrino oscillations equations in matter is proposed. The computations are speeded up to two orders of magnitude with respect to a general numerical integrator, a fact that could smooth the way for massive numerical integration concomitant with experimental data analyses. Detailed illustrations about numerical procedure and computer time costs are provided.

Brownian motion of a heavy charged particle at zero and small (but finite) temperature is studied in the presence of finite density. We are primarily interested in the dynamics at (near) zero temperature which is holographically described by motion of a fundamental string in a (near-)extremal Reissner-Nordström black hole. We analytically compute the functional form of the retarded Green function for small frequencies and extract the dissipative behavior at and near zero temperature.

Directionally sensitive dark matter (DM) direct detection experiments present the only way to observe the full three-dimensional velocity distribution of the Milky Way halo local to Earth. In this work we compare methods for extracting information about the local DM velocity distribution from a set of recoil directions and energies in a range of hypothetical directional and nondirectional experiments. We compare a model-independent empirical parametrization of the velocity distribution based on an angular discretization with a model-dependent approach which assumes knowledge of the functional form of the distribution. The methods are tested under three distinct halo models which cover a range of possible phase space structures for the local velocity distribution: a smooth Maxwellian halo, a tidal stream and a debris flow. In each case we use simulated directional data to attempt to reconstruct the shape and parameters describing each model as well as the DM particle properties. We find that the empirical parametrization is able to make accurate unbiased reconstructions of the DM mass and cross section as well as capture features in the underlying velocity distribution in certain directions without any assumptions about its true functional form. We also find that by extracting directionally averaged velocity parameters with this method one can discriminate between halo models with different classes of substructure.