In heavy ion collisions, transverse momentum broadening quantifies the modification of a hard probe due to interactions with the quark-gluon plasma (QGP). We calculate momentum broadening in the glasma, which is the highly nonisotropic precursor stage of the QGP right after the collision. We show that the glasma leads to anisotropic momentum broadening: high energy partons accumulate more momentum along the beam axis than transverse to it. The physical origin of anisotropic broadening can be traced back to differences in the shapes of chromoelectric and chromomagnetic flux tubes in the glasma. We provide semianalytic results for momentum broadening in the dilute glasma and numerical results from real-time lattice simulations of the nonperturbative dense glasma.

Black holes past their Page times should act as efficient scramblers and information mirrors. The information of the infalling bits are rapidly encoded by the old black hole in the Hawking quanta, but it should take time that is exponential in the Page time entropy to decode the interior. Motivated by the features of fragmentation instability of near-extremal black holes, we construct a simple phenomenological model of the black hole as a lattice of interacting nearly ${\mathrm{AdS}}_2$ throats with gravitational hair charges propagating over the lattice. We study the microstate solutions and their response to shocks. The energy of the shocks are almost wholly absorbed by the total Arnowitt-Deser-Misner mass of the ${\mathrm{AdS}}_2$ throats, but the information of their locations and time ordering come out in the hair oscillations, which decouple from the final microstate to which the full system quickly relaxes. We discuss the Hayden-Preskill protocol of decoding infalling information. We also construct generalizations of our model involving a lattice of ${\mathrm{AdS}}_2$ throats networked via wormholes and their analogs in the form of tensor networks of Sachdev-Ye-Kitaev spin states.

The low-energy effective theory description of a confining theory, such as QCD, is constructed, including local interactions between hadrons organized in a derivative expansion. This kind of approach also applies more generically to theories with a mass gap, once the relevant low-energy degrees of freedom are identified. The strength of local interactions in the effective theory is determined by the low-momentum expansion of scattering amplitudes, with the scattering length capturing the leading order. We compute the main contribution to the scattering length between two spin-zero particles in strongly coupled theories using the gauge/gravity duality. We study two different theories with a mass gap: a massive deformation of $\mathcal{N}=4$ super-Yang-Mills theory ($\mathcal{N}=1^{*}$) and a nonsupersymmetric five-dimensional theory compactified on a circle. These cases have a different realization of the mass gap in the dual gravity description: the former is the well-known GPPZ singular solution and the latter a smooth ${\mathrm{AdS}}_6$ soliton geometry. We find that the scattering lengths have similar functional dependences on the masses of the particles and on the conformal dimension of the operators that create them in both theories. Assuming these similarities hold more generally, they could be used to constrain the effective description of gapped strongly coupled theories beyond symmetry considerations.

A correspondence between closed strings in their high-temperature Hagedorn phase and asymptotically de Sitter (dS) space is established. We identify a thermal, conformal field theory (CFT) whose partition function is, on the one hand, equal to the partition function of closed, interacting, fundamental strings in their Hagedorn phase yet is, on the other hand, also equal to the Hartle-Hawking (HH) wave function of an asymptotically dS universe. The Lagrangian of the CFT is a functional of a single scalar field, the condensate of a thermal scalar, which is proportional to the entropy density of the strings. The correspondence has some aspects in common with the anti–de Sitter/CFT correspondence, as well as with some of its proposed analytic continuations to a $\mathrm{dS}/\mathrm{CFT}$ correspondence, but it also has some important conceptual and technical differences. The equilibrium state of the CFT is one of maximal pressure and entropy, and it is at a temperature that is above but parametrically close to the Hagedorn temperature. The CFT is valid beyond the regime of semiclassical gravity and thus defines the initial quantum state of the dS universe in a way that replaces and supersedes the HH wave function. Two-point correlation functions of the CFT scalar field are used to calculate the spectra of the corresponding metric perturbations in the asymptotically dS universe and, hence, cosmological observables in the postinflationary epoch. Similarly, higher-point correlation functions in the CFT should lead to more complicated cosmological observables.

We investigate the existence of self-dual solitons with internal structure in a gauged $O(3)$ nonlinear sigma model immersed in a dielectric medium generated by a real scalar field (dubbed the source field). We consider rotationally symmetric configurations and applying the Bogomol’nyi-Prasad-Sommerfield formalism to obtain the energy lower bound and the respective first-order differential equations (or self-dual equations). By solving such a system of equations for three different dielectric media, we find the internal structure generates relevant changes in the soliton profiles when compared with the ones obtained without the presence of the dielectric medium.

In this paper we have investigated the dynamics of neutral, electrically charged and magnetized particles around renormalized group improved (RGI) Schwarzschild black hole in the presence of external asymptotically uniform magnetic field. We have analyzed the spacetime structure around RGI black hole by investigating Ricci, the square of Ricci tensor and Kretschmann curvature scalars and shown that only in the case when the parameter $\gamma =0$ the curvature becomes infinite at the center of the black hole, while for nonzero values of $\gamma$ parameter the black hole curvature reflects the properties of regular black hole. Analyzing the innermost stable circular orbits of test neutral particles around RGI black hole and comparing with the results for rotating Kerr black hole we have shown that RGI black hole parameters can mimic the rotation parameter of Kerr black hole up to $a/M\lesssim 0.31$ providing the same innermost stable circular orbit (ISCO) radius. Since according to the astronomical observations of the accretion disks confirm that the astrophysical black holes are rapidly rotating with the spin parameter up to $a/M\sim 0.99$ one may conclude that the effects of parameters of RGI Schwarzschild black hole on the circular orbits of the neutral particles cannot mimic the Kerr black hole. Then the Hamilton-Jacobi equation has been used to analyze the charged and magnetized particles motion near the RGI black hole in the presence of the strong interaction between external asymptotically uniform magnetic (electromagnetic) field and magnetized (electrically charged) particle. We have shown that RGI black hole parameters quantitatively change the dynamics of the charged and magnetized particles, in particular ISCO radius of the particles decreases with increasing the parameter $\lambda$, while the increase of the parameter $\gamma$ causes to increase of it. The stability analysis of the circular orbits of the magnetized particles has shown that the population of magnetars with the strong surface magnetic field up to ${10}^{15}$ Gauss is excluded from the very close environment of a supermassive black hole due to destructive properties of the magnetic field.

We investigate spin- and velocity-dependent contributions to the gravitational interparticle potential. The methodology adopted here is based on the expansion of the effective action in terms of form factors encoding quantum corrections. Restricting ourselves to corrections up to the level of the graviton propagator, we compute, in terms of general form factors, the nonrelativistic gravitational potential associated with the scattering of spin-0 and $\text{−}1/2$ particles. We discuss comparative aspects concerning different types of scattered particles and we also establish some comparisons with the case of electromagnetic potentials. Moreover, we apply our results to explicit examples of form factors based on nonperturbative approaches for quantum gravity. Finally, the cancellation of Newtonian singularity is analyzed in the presence of terms beyond the monopole-monopole sector.

In this work, we make the first step to derive nonradial pulsation equations in extra dimensions and investigate how the $f$- and $p_1$-mode frequencies of strange quark stars, within the Cowling approximation, change with the number of dimensions. In this regard, the study is performed by solving numerically the nonradial pulsation equations, adjusted for a $d$-dimensional spacetime ($d\ge 4$). We connect the interior to a Schwarzschild-Tangherlini exterior metric and analyze the $f$- and $p_1$- mode frequencies. We found that the frequencies could become higher than those found in four-dimensional spacetime. The $f$-mode frequency is essentially constant and only for large gravitational radius values grows monotonically and fast with the gravitational radius. In a gravitational radius range, where $f$-mode frequencies are constant, they increase for spacetime dimensions $4\le d\le 6$ and decrease for $d\ge 7$. Regarding $p_1$-mode frequencies they are always larger for higher dimensions and decay monotonically with the increase of the gravitational radius. In extra dimensions, as it happens for four-dimensional spacetime, we found $p_1$-mode frequencies are always larger than the $f$-modes ones. In the Newtonian gravity, for a homogeneous star in $d$ dimensions, we observe that the $f$-mode eigenfrequencies are constant and given by the relation ${\omega }^2=lM{G}_d/R^{d-1}$, where $l$ represents the spherical harmonic index, $M{G}_d$ is the total star mass and $R$ the stellar radius. For some gravitational radius interval, we show that a homogeneous star in Newtonian gravity is a good approximation to investigate the $f$-mode frequency of strange stars in the relativistic frame. In each dimension considered, we find that the $f$-mode frequencies of strange stars are essentially constant since they depend on the average star energy density that is almost constant as a function of the total star mass. Moreover, for a fixed energy density, we also find that the $f$-mode frequency changes with the volume of the unitary sphere in the $d-1$ dimension, which attains its maximum value at $d=6$. In neutron stars in four dimensions, where the average energy density of the star increases with the central energy density, the $f$-mode frequencies will increase with the star mass. Thus, the possibility to measure in gravitational wave detectors the $f$-mode oscillation frequency coming from compact stars with different pulsar masses and observe almost constant frequency values, for $d=4$, in the range $f\sim 2–3[\mathrm{kHz}]$ with $M\le 1.8M_{\odot }$, it would be a good sign of the existence of strange quark stars that still lack an astronomical confirmation. Finally, if the $f$-mode frequencies are still constant and different from the range values of $d=4$ for larger total masses, it would be evidence that quarks can propagate in extra spacetime dimensions and strange quark stars in $d$ dimension could exist.

We study propagation of high-frequency electromagnetic waves in a curved spacetime. We demonstrate how a modification of the standard geometric optics allows one to include the helicity dependent corrections into the equations of motion of circularly polarized beams of radiation. As a result, polarized light rays are still null but not geodesic curves. To achieve these results we construct null frames associated with a set of (nongeodesic) null rays and use these frames for a description of the high-frequency wave propagation. We call this approach spin optics approximation. It is completely covariant and it can be used in an arbitrary time-dependent gravitational field.

We systematically investigate the complete class of vacuum solutions in the Einstein-Gauss-Bonnet (EGB) gravity theory which belong to the Kundt family of nonexpanding, shear-free, and twist-free geometries (without gyratonic matter terms) in any dimension. The field equations are explicitly derived and simplified, and their solutions classified into three distinct subfamilies. Algebraic structures of the Weyl and Ricci curvature tensors are determined. The corresponding curvature scalars directly enter the invariant form of the equation of geodesic deviation, enabling us to understand the specific local physical properties of the gravitational field constrained by the EGB theory. We also present and analyze several interesting explicit classes of such vacuum solutions, namely, the Ricci type-III spacetimes, all geometries with constant-curvature transverse space, and the whole pp-wave class admitting a covariantly constant null vector field. These exact Kundt EGB gravitational waves exhibit new features which are not possible in Einstein’s general relativity.

Einstein-Cartan theory is an extension of the standard formulation of general relativity characterized by a nonvanishing torsion. The latter is sourced by the matter fields via the spin tensor, and its effects are expected to be important at very high spin densities. In this work, we analyze in detail the physics of Einstein-Cartan theory with Dirac and Maxwell fields minimally coupled to the spacetime torsion. This breaks the $U(1)$ gauge symmetry, which is suggested by the possibility of a torsion-induced phase transition in the early Universe. The resulting Dirac-like and Maxwell-like equations are nonlinear with self-interactions as well as having fermion-boson nonminimal couplings. We discuss several cosmological aspects of this theory under the assumption of randomly oriented spin densities (unpolarized matter), including bounces, acceleration phases, and matter-antimatter asymmetry in the torsion era, as well as late-time effects such as the generation of an effective cosmological constant, dark energy, and future bounces within cyclic solutions.

We propose a new class of Proca interactions that enjoy a nontrivial constraint and hence propagates the correct number of degrees of freedom for a healthy massive spin-1 field. We show that the scattering amplitudes always differ from those of the Generalized Proca. This implies that the new class of interactions proposed here are genuinely different from the Generalized Proca and there can be no local field redefinitions between the two. In curved spacetime, massive gravity is the natural covariantization, but we show how other classes of covariantizations can be considered.

In this paper we study some models where non-Abelian gauge vector fields endowed with a SU(2) group representation are the unique source of inflation and dark energy. These models were first introduced under the name of gaugeflation and gaugessence, respectively. Although several realizations of these models have been discussed, not all available parameters and initial conditions are known. In this work, we use a dynamical system approach to find the full parameter space of the massive version of each model. In particular, we found that the inclusion of the mass term increases the length of the inflationary period. Additionally, the mass term implies new behaviors for the equation of state of dark energy allowing to distinguish this from other prototypical models of accelerated expansion. We show that an axially symmetric gauge field can support an anisotropic accelerated expansion within the observational bounds.

The brightness of the tip of the red-giant branch (TRGB) allows one to constrain novel energy losses that would lead to a larger core mass at helium ignition and, thus, to a brighter TRGB than expected by standard stellar models. The required absolute TRGB calibrations strongly improve with reliable geometric distances that have become available for the galaxy NGC 4258 that hosts a water megamaser and to the Large Magellanic Cloud based on 20 detached eclipsing binaries. Moreover, we revise a previous TRGB calibration in the globular cluster $\omega$ Centauri with a recent kinematical distance determination based on Gaia data release 2. All of these calibrations have similar uncertainties, and they agree with each other and with recent dedicated stellar models. Using NGC 4258 as the cleanest extragalactic case, we thus find an updated constraint on the axion-electron coupling of $g_{ae}<1.6\times {10}^{-13}$ and ${\mu }_{\nu }<1.5\times {10}^{-12}{\mu }_{\mathrm{B}}$ (95% C.L.) on a possible neutrino dipole moment, whereas $\omega$ Centauri as the best galactic target provides instead $g_{ae}<1.3\times {10}^{-13}$ and ${\mu }_{\nu }<1.2\times {10}^{-12}{\mu }_{\mathrm{B}}$. The reduced observational errors imply that stellar evolution theory and bolometric corrections begin to dominate the overall uncertainties.

A dark matter overdensity around a black hole may significantly alter the dynamics of the black hole’s merger with another compact object. We consider here intermediate mass-ratio inspirals of stellar-mass compact objects with intermediate-mass black holes “dressed” with dark matter. We first demonstrate that previous estimates based on a fixed dark-matter dress are unphysical for a range of binaries and dark-matter distributions by showing that the total energy dissipated by the compact object through dynamical friction, as it inspirals through the dense dark matter environment toward the black hole, is larger than the gravitational binding energy of the dark-matter dress itself. We then introduce a new formalism that allows us to self-consistently follow the evolution of the dark-matter dress due to its gravitational interaction with the binary. We show that the dephasing of the gravitational waveform induced by dark matter is smaller than previously thought, but is still potentially detectable with the LISA space interferometer. The gravitational waves from such binaries could provide powerful diagnostics of the particle nature of dark matter.

Neutron star (NS) binaries formed dynamically may have significant eccentricities while emitting gravitational waves (GWs) in the LIGO/VIRGO band. We study tidal effects in such eccentric inspiralling NS binaries using a set of hybrid equations. The NS is modeled as a compressible ellipsoid, which can deform nonlinearly due to tidal forces, while the orbit evolution is treated with the post-Newtonian (PN) theory up to 2.5-PN order. We find that in general, the tidal interaction can accelerate the inspiral, and cause orbital frequency and phase shifts. For circular inspirals, our calculations reproduce previous linear result at large binary separations, but incorporate the dynamical response of the NS at small separations. For eccentric inspirals, the frequency and phase shifts oscillate considerably near pericenter passages, and the oscillating amplitudes increase with eccentricities. As a result, the GW phase is also significantly influenced by the tidal effect. At merger, the cumulative GW phase shift can reach more than 10 radians (for typical NS mass $1.4M_{\odot }$ and radius 11.6 km), much larger than the circular inspiral case. Although the event rate of eccentric NS mergers is likely low, the detection of such mergers could provide a useful constraint on the NS equation of state.

Recently there has been increasing interest in alternate methods to compute quantum tunneling in field theory. Of particular interest is a stochastic approach which involves (i) sampling from the free theory Gaussian approximation to the Wigner distribution in order to obtain stochastic initial conditions for the field and momentum conjugate and then (ii) evolving under the classical field equations of motion, which leads to random bubble formation. Previous work showed parametric agreement between the logarithm of the tunneling rate in this stochastic approach and the usual instanton approximation. However, recent work [J. Braden et al., Phys. Rev. Lett. 123, 031601 (2019)] claimed excellent agreement between these methods. Here we show that this approach does not in fact match precisely; the stochastic method tends to overpredict the instanton tunneling rate. To quantify this, we parameterize the standard deviations in the initial stochastic fluctuations by $ϵ\sigma$, where $\sigma$ is the actual standard deviation of the Gaussian distribution and $ϵ$ is a fudge factor; $ϵ=1$ is the physical value. We numerically implement the stochastic approach to obtain the bubble formation rate for a range of potentials in $1+1$ dimensions, finding that $ϵ$ always needs to be somewhat smaller than unity to suppress the otherwise much larger stochastic rates toward the instanton rates; for example, in the potential of Braden et al., one needs $ϵ\approx 1/2$. We find that a mismatch in predictions also occurs when sampling from other Wigner distributions and in single-particle quantum mechanics even when the initial quantum system is prepared in an exact Gaussian state. If the goal is to obtain agreement between the two methods, our results show that the stochastic approach would be useful if a prescription to specify optimal fudge factors for fluctuations can be developed.

Recently, Poole and Thomsen presented the renormalization group equations (RGEs) in the $\overline{\mathrm{MS}}$ scheme for dimensionless parameters of a general renormalizable gauge theory in a new formalism based on the local renormalization group. In this paper, we apply the dummy field method to the expressions in this formalism in order to derive the RGEs for the dimensionful couplings, which so far have been missing in this approach. The complete set of RGEs has been implemented in a new version of the public code pyr@te dedicated to the automatic computation of the RGEs for any general renormalizable (nonsupersymmetric) gauge theory.

We point out a problem of the phenomenological definition of the valence partons as the difference between the partons and antipartons in the context of the next-to-next-leading-order evolution equations. After demonstrating that the classification of the parton degrees of freedom (PDF) of the parton distribution functions (PDFs) are the same in the QCD path-integral formulations of the hadronic tensor and the quasi-PDF with large momentum effective theory (LaMET), we resolve the problem by showing that the proper definition of the valence partons should be in terms of those in the connected insertions only. We also prove that the strange partons appear as the disconnected sea in the nucleon.