We study gravitational waves with torsion as exact vacuum solutions of three-dimensional gravity with propagating torsion. The new solutions are a natural generalization of the plane-fronted gravitational waves in general relativity with a cosmological constant, in the presence of matter.

I show that radiative space-times are not asymptotically flat; rather, the radiation field gives rise to holonomy at null infinity. (This was noted earlier, by Bramson.) This means that when gravitational radiation is present, asymptotically covariantly constant vector fields do not exist. On the other hand, according to the Bondi-Sachs construction, a weaker class of asymptotically constant vectors does exist. Reconciling these concepts leads to a measure of the scattering of matter by gravitational waves, that is, bulk exchanges of energy-momentum between the waves and matter. Because these bulk effects are potentially larger than the tidal ones which have usually been studied, they may affect the waves’ propagation more significantly, and the question of matter’s transparency to gravitational radiation should be revisited. While in many cases there is reason to think the waves will be only slightly affected, some situations are identified in which the energy-momentum exchanges can be substantial enough that a closer investigation should be made. In particular, the work here suggests that gravitational waves produced when relativistic jets are formed might be substantially affected by passing through an inhomogeneous medium.

We study the orbital and epicyclic frequencies of particles orbiting around rapidly rotating neutron stars and strange stars in a particular scalar-tensor theory of gravity. We find very large deviations of these frequencies, when compared to their corresponding values in general relativity, for the maximum-mass rotating models. In contrast, for models rotating with spin frequency of 700 Hz (approximately the largest known rotation rate of neutron stars), the deviations are generally small. Nevertheless, for a very stiff equation of state and a high mass, the deviation of one of the epicyclic frequencies from its GR value is appreciable even at a spin frequency of 700 Hz. In principle, such a deviation could become important in models of quasiperiodic oscillations in low-mass x-ray binaries and could serve as a test of strong gravity (if other parameters are well constrained). Even though the present paper is concentrated mainly on orbital and epicyclic frequencies, we present here for the first time rapidly rotating, scalarized equilibrium compact stars with realistic hadronic equations of state and strange matter equation of state. We also provide analytical expressions for the exterior spacetime of scalarized neutron stars and their epicyclic frequencies in the nonrotating limit.

We investigate the dynamics of a family of functional extensions of the (Eddington-inspired) Born-Infeld gravity theory, constructed with the inverse of the metric and the Ricci tensor. We provide a generic formal solution for the connection and an Einstein-like representation for the metric field equations of this family of theories. For particular cases we consider applications to the early-time cosmology and find that nonsingular universes with a cosmic bounce are very generic and robust solutions.

The late collapse, core bounce, and the early postbounce phase of rotating core collapse leads to a characteristic gravitational wave (GW) signal. The precise shape of the signal is governed by the interplay of gravity, rotation, nuclear equation of state (EOS), and electron capture during collapse. We explore the detailed dependence of the signal on total angular momentum and its distribution in the progenitor core by means of a large set of axisymmetric general-relativistic hydrodynamics core-collapse simulations, in which we systematically vary the initial angular momentum distribution in the core. Our simulations include a microphysical finite-temperature EOS, an approximate electron capture treatment during collapse, and a neutrino leakage scheme for the postbounce evolution. Our results show that the total angular momentum of the inner core at bounce and the inner core’s ratio of rotational kinetic energy to gravitational energy $T/|W|$ are both robust parameters characterizing the GW signal. We find that the precise distribution of angular momentum is relevant only for very rapidly rotating cores with $T/|W|\gtrsim 8\%$ at bounce. We construct a numerical template bank from our baseline set of simulations, and carry out additional simulations to generate trial waveforms for injection into simulated Advanced LIGO noise at a fiducial galactic distance of 10 kpc. Using matched filtering, we show that for an optimally oriented source and Gaussian noise, Advanced LIGO could measure the total angular momentum to within $\pm 20\%$, for rapidly rotating cores. For most waveforms, the nearest known degree of precollapse differential rotation is correctly inferred by both our matched filtering analysis and an alternative Bayesian model selection approach. We test our results for robustness against systematic uncertainties by injecting waveforms from simulations utilizing a different EOS and variations in the electron fraction in the inner core. The results of these tests show that these uncertainties significantly reduce the accuracy with which the total angular momentum and its precollapse distribution can be inferred from observations.

We derive a set of equations monitoring the evolution of covariant and gauge-invariant linear scalar perturbations of Friedman-Lemaître-Robertson-Walker models with multiple interacting nonlinear scalar fields. We use a dynamical systems approach in order to perform a stability analysis for some classes of scalar field potentials. In particular, using a recent approximation for the inflationary dynamics of the background solution, we derive conditions under which homogenization occurs for chaotic (quadratic and quartic potentials) and new inflation. We also prove a cosmic no-hair result for power-law inflation and its generalization for two scalar fields with independent exponential potentials (assisted power-law inflation).

The cosmic neutrino background ($\mathrm{C}\nu \mathrm{B}$), produced about one second after the big bang, permeates the Universe today. New technological advancements make neutrino capture on beta-decaying nuclei (NCB) a clear path forward towards the detection of the $\mathrm{C}\nu \mathrm{B}$. We show that gravitational focusing by the Sun causes the expected neutrino capture rate to modulate annually. The amplitude and phase of the modulation depend on the phase-space distribution of the local neutrino background, which is perturbed by structure formation. These results also apply to searches for sterile neutrinos at NCB experiments. Gravitational focusing is the only source of modulation for neutrino capture experiments, in contrast to dark-matter direct-detection searches where the Earth’s time-dependent velocity relative to the Sun also plays a role.

We attempt to describe the interplay of confinement and chiral symmetry breaking in QCD by using the string model. We argue that in the quasi-Abelian picture of confinement based on the condensation of magnetic monopoles and the dual Meissner effect, the world sheet dynamics of the confining string can be effectively described by the $1+1$ dimensional massless electrodynamics, which is exactly soluble. The transverse plane distribution of the chromoelectric field stretched between the quark and antiquark sources can then be attributed to the fluctuations in the position of the string. The dependence of the chiral condensate in the string on the (chromo-)electric field can be evaluated analytically, and is determined by the chiral anomaly and the $\theta$-vacuum structure. Therefore, our picture allows us to predict the distribution of the chiral condensate in the plane transverse to the axis connecting the quark and antiquark. This prediction is compared to the lattice QCD results; a good agreement is found.

We perform a statistical analysis of the full set of parity-violating asymmetry data for elastic electron scattering including the most recent high precision measurement from $Q$-weak. Given the basis of the present analysis, our estimates appear to favor nonzero vector strangeness, specifically, positive (negative) values for the electric (magnetic) strange form factors. We also provide an accurate estimate of the axial-vector nucleon form factor at zero momentum transfer, $G_A^{ep}(0)$. Our study shows $G_A^{ep}(0)$ to be importantly reduced with respect to the currently accepted value. We also find our analysis of data to be compatible with the Standard Model values for the weak charges of the proton and neutron.

Radiative effects in the electroproduction of photons in polarized $ep$ scattering are calculated with next-to-leading-order accuracy. The contributions of loops and two-photon emission are presented in analytical form. The covariant approach of Bardin and Shumeiko is used to extract the infrared divergence. All contributions to the radiative correction are presented in the form of the correction to the leptonic tensor thus allowing for further applications in other experiments, e.g., deep inelastic scattering. The radiative corrections to the cross sections and polarization asymmetries are analyzed numerically for the kinematical conditions of the current measurement at Jefferson Lab. Specific attention is paid to analyzing kinematical conditions for the process with a large radiative effect when the momenta of two photons in the final state are collinear with the momenta of the initial and final electrons, respectively.

The $e^{+}{e}^{-}\to \eta \gamma$ cross section has been measured in the center-of-mass energy range 1.07–2.00 GeV using the decay mode $\eta \to 3{\pi }^0$, ${\pi }^0\to \gamma \gamma$. The analysis is based on $36{\mathrm{pb}}^{-1}$ of integrated luminosity collected with the SND detector at the VEPP-2000 $e^{+}{e}^{-}$ collider. The measured cross section of about 40 pb at 1.5 GeV is explained by decays of the $\rho (1450)$ and $\varphi (1680)$ resonances.

Given that the scale of quantum gravity is not experimentally accessible, one naturally resorts to mathematical consistency as a measure for a good candidate theory to replace general relativity at high energies. Reproducing the semiclassical results of black hole entropy has become a standard test for any prospective theory of quantum gravity. It is often argued that another such commonality, albeit less known, is the similar fractal behavior. It is shown that many, if not all, approaches to quantum gravity predict a spectral dimension of 2 in ultraviolet regime. In this paper, by computing the heat kernel, we show that the spectral dimension of closed bosonic string theory is 26. We discuss the implications of this disparity.

We argue that the recently proposed principle of relative locality offers a new way to resolve the black hole information puzzle.

We explicitly test the equal-time consistency relation between the angular-averaged bispectrum and the power spectrum of the matter density field, employing a large suite of cosmological $N$-body simulations. This is the lowest-order version of the relations between $(\ell +n)$-point and $n$-point polyspectra, where one averages over the angles of $\ell$ soft modes. This relation depends on two wave numbers, $k^{\prime }$ in the soft domain and $k$ in the hard domain. We show that it holds up to a good accuracy, when $k^{\prime }/k\ll 1$ and $k^{\prime }$ is in the linear regime, while the hard mode $k$ goes from linear ($0.1h{\mathrm{Mpc}}^{-1}$) to nonlinear ($1.0h{\mathrm{Mpc}}^{-1}$) scales. On scales $k\lesssim 0.4h{\mathrm{Mpc}}^{-1}$, we confirm the relation within the statistical error of the simulations (typically a few percent depending on the wave number), even though the bispectrum can already deviate from leading-order perturbation theory by more than 30%. We further examine the relation on smaller scales with higher resolution simulations. We find that the relation holds within the statistical error of the simulations at $z=1$, whereas we find deviations as large as $\sim 7\%$ at $k\sim 1.0h{\mathrm{Mpc}}^{-1}$ at $z=0.35$. We show that this can be explained partly by the breakdown of the approximation ${\mathrm{\Omega }}_{\mathrm{m}}/f^2\simeq 1$ with supplemental simulations done in the Einstein–de Sitter background cosmology. We also estimate the impact of this approximation on the power spectrum and bispectrum.

We consider explicit unified models based on the “flipped” $SU(5)\times U(1)$ and $SU(6)\times SU(2)$ gauge groups in which gauge mediated proton decay operators are suppressed at leading order due to the special placement of matter fields in unified multiplets. We discuss both the theoretical structure and phenomenological implications of these models. For the latter, we examine the viability of the physical spectrum in each scenario and focus on the possible presence of other operators that could also contribute significantly to the proton decay rate.

It has recently been demonstrated that a program of parasitic electron-beam fixed-target experiments would have powerful discovery potential for dark matter and other new weakly coupled particles in the MeV-GeV mass range. The first stage of this program can be realized at Jefferson Laboratory using an existing plastic-scintillator detector downstream of the Hall D electron beam dump. This paper studies the physics potential of such an experiment and highlights its unique sensitivity to inelastic “exciting” dark matter and leptophilic dark matter scenarios. The first of these is kinematically inaccessible at traditional direct detection experiments and features potential “smoking gun” low-background signatures.

We derive the one-loop matching condition for nonsinglet quark distributions in the transverse-momentum cutoff scheme, including unpolarized, helicity and transversity distributions. The matching is between the quasidistribution defined by static correlation at finite nucleon momentum and the light-cone distribution measurable in experiments. The result is useful for extracting the latter from the former in a lattice QCD calculation which uses the lattice spacing as the ultraviolet cutoff.

In this work we illustrate how form-invariance transformations (FITs) can be used to construct phantom and complementary tachyon cosmologies from standard tachyon field universes. First we show how these transformations act on the Hubble expansion rate, and the energy density and pressure of the tachyon field. Then we use the FIT to generate three different families of the tachyon field. In other words, the FIT generates new cosmologies from a known “seed” one; in particular, we apply the FIT to the ordinary tachyon field to obtain two types of tachyon species, denoted as the phantom and complementary tachyons. We see that the FIT allows us to pass from a nonstable cosmology to a stable one and vice versa. Finally, as an example, we apply the transformations to an inverse-square potential, $V\propto {\varphi }^{-2}$, and generate the extended tachyon field.

A black hole casts a shadow as an optical appearance because of its strong gravitational field. We study the shadow cast by the five-dimensional Myers-Perry black hole with equal rotation parameters. We demonstrate that the null geodesic equation can be integrated, which provides us an opportunity to investigate the shadow cast by a black hole. The shadow of a black hole is found to be a dark zone covered by a deformed circle. Interestingly, the shapes of the black hole shadow are more distorted and the size decreases for larger black hole spins. Interestingly, it turns out that, for fixed values of the rotation parameter, the shadow is slightly smaller and less deformed than for its four-dimensional Kerr black hole counterpart. Further, the shadow of the five-dimensional Kerr black hole is concentric deformed circles. The effect of the rotation parameter on the shape and size of a naked singularity shadow is also analyzed.