Using $e^{+}{e}^{-}$ annihilation data taken at the CESR collider with the CLEO-c detector, measurements of hyperon pair production cross sections and elastic and transition electromagnetic form factors have been made at the charmonium resonances: $\psi (2S)$, $\sqrt{s}=3.69\mathrm{GeV}$, $|Q^2|=13.6{\mathrm{GeV}}^2$, $\mathcal{L}=48{\mathrm{pb}}^{-1}$; $\psi (3770)$, $\sqrt{s}=3.77\mathrm{GeV}$, $|Q^2|=14.2{\mathrm{GeV}}^2$, $\mathcal{L}=805{\mathrm{pb}}^{-1}$; and $\psi (4170)$, $\sqrt{s}=4.17\mathrm{GeV}$, $|Q^2|=17.4{\mathrm{GeV}}^2$, $\mathcal{L}=586{\mathrm{pb}}^{-1}$. Results with good statistical precision are obtained with high efficiency particle identification. Systematics of pair production cross sections, and form factors with respect to the number of strange quarks in the hyperons are studied, and evidence is presented for the effects of diquark correlations in comparative results for ${\mathrm{\Lambda }}^0$ and ${\mathrm{\Sigma }}^0$, both of which have the same $uds$ quark content but different isospin.

We consider the generalization of the $S$-duality transformation previously investigated in the context of the fractional quantum Hall effect (FQHE) and $s$-wave superconductivity to $p$-wave superconductivity in $2+1$ dimensions in the framework of the $\mathrm{AdS}/\mathrm{CFT}$ correspondence. The vector Cooper condensate transforms under the $S$-duality action to the pseudovector condensate at the dual side. The $3+1$-dimensional Einstein-Yang-Mills theory, the holographic dual to $p$-wave superconductivity, is used to investigate the $S$-duality action via the $\mathrm{AdS}/\mathrm{CFT}$ correspondence. It is shown that, in order to implement the duality transformation, chemical potentials on both the electric and magnetic sides of the duality have to be introduced. A relation for the product of the non-Abelian conductivities in the dual models is derived. We also conjecture a flavor $S$-duality transformation in the holographic dual to $3+1$-dimensional QCD low-energy QCD with non-Abelian flavor gauge groups. The conjectured $S$-duality interchanges isospin and baryonic chemical potentials.

In this paper, considering the linearized Einstein equation with a two-parameter family of linear covariant gauges in de Sitter spacetime, we examine possible vacuum states for the gravitons field with respect to invariance under the de Sitter group $S{O}_0(1,4)$. Our calculations explicitly reveal that there exists no natural de Sitter-invariant vacuum state (the Euclidean or Bunch-Davies state) for the gravitons field. Indeed, on the foundation of a rigorous group-theoretical reasoning, we prove that if one insists on full covariance as well as causality for the theory, one has to give up the positivity requirement of the inner product. However, one may still look for states with as much symmetry as possible, more precisely, a restrictive version of covariance by considering the gravitons field and the associated vacuum state which are, respectively, covariant and invariant with respect to some maximal subgroup of the full de Sitter group. In this regard, we treat the $SO(4)$ case and find a family of $SO(4)$-invariant states. The associated $SO(4)$-covariant quantum field is given, as well.

This article shows that the compactified Milne universe geometry, a toy model for the big crunch/big bang transition, can be realized in hyperbolic metamaterials, a new class of nanoengineered systems which have recently found its way as an experimental playground for cosmological ideas. On one side, Klein-Gordon particles, as well as tachyons, are used as probes of the Milne geometry. On the other side, the propagation of light in two versions of a liquid crystal-based metamaterial provides the analogy. It is shown that ray and wave optics in the metamaterial mimic, respectively, the classical trajectories and wave function propagation, of the Milne probes, leading to the exciting perspective of realizing experimental tests of particle tunneling through the cosmic singularity, for instance.

We determine the asymptotic symmetry group of Killing horizons by choosing Gaussian null coordinates in the neighborhood of the horizon and boundary conditions that respect the leading-order terms in the metric. The analysis divides naturally into the two cases of subextremal and extremal horizons. In general, we find rather involved asymptotic symmetry generators that nevertheless involve supertranslations and Killing vectors on the compact horizon. The most striking observation is the difference in the dependence on the coordinate along the horizon; we relate this to the redshift effect for subextremal horizons. We consider the spherically symmetric case as a special and illuminating example.

We generalize the mechanism for gravitational baryogensis in the context of $f(R)$ theories of gravity, including a nonminimal coupling between curvature and matter. In these models, the baryon asymmetry is generated through an effective coupling between the Ricci scalar curvature and the net baryon current that dynamically breaks Charge conjugation, parity and time reversal ($CPT$) invariance. We study the combinations of characteristic mass scales and exponents for both nontrivial functions present in the modified action functional and establish the allowed region for these parameters: we find that very small deviations from general relativity are consistent with the observed baryon asymmetry and lead to temperatures compatible with the subsequent formation of the primordial abundances of light elements. In particular, we show the viability of a power-law nonminimal coupling function $f_2(R)\sim R^n$ with $0<n\lesssim 0.078$ and determine its characteristic curvature scale.

The implications of two different time constraints on the Mathisson-Papapetrou-Dixon (MPD) equations are discussed under three spin supplementary conditions (SSCs). For this reason the MPD equations are revisited without specifying the affine parameter and several relations are reintroduced in their general form. The latter allows one to investigate the consequences of combining the Mathisson-Pirani (MP) SSC, the Tulczyjew-Dixon (TD) SSC and the Ohashi-Kyrian-Semerák (OKS) SSC with two affine parameter types: the proper time on one hand and the parameterizations introduced in [Gen. Relativ. Gravit. 8, 197 (1977)] on the other. For the MP SSC and the TD SSC it is shown that quantities that are constant of motion for the one affine parameter are not for the other, while for the OKS SSC it is shown that the two affine parameters are the same. To clarify the relation between the two affine parameters in the case of the TD SSC the MPD equations are evolved and discussed.

We introduce three approaches to generate curvature invariants that transform covariantly under a conformal transformation of a four-dimensional spacetime. For any black hole conformally related to a stationary black hole, we show how a set of conformally covariant invariants can be combined to produce a conformally covariant invariant that detects the event horizon of the conformally related black hole. As an application we consider the rotating dynamical black holes conformally related to the Kerr-Newman-Unti-Tamburino–(anti)-de Sitter spacetimes and construct an invariant that detects the conformal Killing horizon along with a second invariant that detects the conformal stationary limit surface. In addition, we present necessary conditions for a dynamical black hole to be conformally related to a stationary black hole and apply these conditions to the ingoing Kerr-Vaidya and Vaidya black hole solutions to determine if they are conformally related to stationary black holes for particular choices of the mass function. While two of the three approaches cannot be generalized to higher dimensions, we discuss the existence of a conformally covariant invariant that will detect the event horizon for any higher dimensional black hole conformally related to a stationary black hole which admits at least two conformally covariant invariants, including all vacuum spacetimes.

Chemical equilibrium is a commonly made assumption in the freeze-out calculation of coannihilating dark matter. We explore the possible failure of this assumption and find a new conversion-driven freeze-out mechanism. Considering a representative simplified model inspired by supersymmetry with a neutralinolike and sbottomlike particle we find regions in parameter space with very small couplings accommodating the measured relic density. In this region freeze-out takes place out of chemical equilibrium and dark matter self-annihilation is thoroughly inefficient. The relic density is governed primarily by the size of the conversion terms in the Boltzmann equations. Due to the small dark matter coupling the parameter region is immune to direct detection but predicts an interesting signature of disappearing tracks or displaced vertices at the LHC. Unlike freeze-in or superWIMP scenarios, conversion-driven freeze-out is not sensitive to the initial conditions at the end of reheating.

Recent developments in bigravity allow one to construct consistent theories of interacting spin-2 particles that are free of ghosts. In this framework, we propose an elementary spin-2 dark matter candidate with a mass well below the TeV scale. We show that, in a certain regime where the interactions induced by the spin-2 fields do not lead to large departures from the predictions of general relativity, such a light dark matter particle typically self-interacts and undergoes self-annihilations via 3-to-2 processes. We discuss its production mechanisms and also identify the regions of the parameter space where self-interactions can alleviate the discrepancies at small scales between the predictions of the collisionless dark matter paradigm and cosmological N-body simulations.

We propose a general method to self-consistently study the quasistationary evolution of the magnetic field in the cores of neutron stars. The traditional approach to this problem is critically revised. Our results are illustrated by calculation of the typical timescales for the magnetic field dissipation as functions of temperature and the magnetic field strength.

Outcomes of numerical relativity simulations of massive core collapses or binary neutron star mergers with moderate masses suggest formations of rapidly and differentially rotating neutron stars. Subsequent fall back accretion may also amplify the degree of differential rotation. We propose new formulations for modeling the differential rotation of those compact stars, and present selected solutions of differentially rotating, stationary, and axisymmetric compact stars in equilibrium. For the cases when rotating stars reach break-up velocities, the maximum masses of such rotating models are obtained.

In this paper we provide an experimental illustration of Page and Wootters’ quantum time mechanism that is able to describe two-time quantum correlation functions. This allows us to test a Leggett-Garg inequality, showing a violation from the “internal” observer point of view. The “external” observer sees a time-independent global state. Indeed, the scheme is implemented using a narrow-band single photon where the clock degree of freedom is encoded in the photon’s position. Hence, the internal observer that measures the position can track the flow of time, while the external observer sees a delocalized photon that has no time evolution in the experiment time-scale.

We propose a generalization of the Witten-Dijkgraaf-Verlinde-Verlinde (WDVV) equation from ${\mathbb{R}}^n$ to an arbitrary Riemannian manifold. Its form is obtained by extending the relation of the WDVV equation with $\mathcal{N}=4$ supersymmetric $n$-dimensional mechanics from flat to curved space. The resulting “curved WDVV equation” is written in terms of a third-rank Codazzi tensor. For every flat-space WDVV solution subject to a simple constraint, we provide a curved-space solution on any isotropic space, in terms of the rotationally invariant conformal factor of the metric.

The direct detections of gravitational waves (GW) from merging binary black holes (BBH) by aLIGO have brought us a new opportunity to utilize BBH for a measurement of the Hubble constant. In this paper, we point out that there exists a small number of BBH that gives significantly small sky localization volume so that a host galaxy is uniquely identified. Then a redshift of a BBH is obtained from a spectroscopic follow-up observation of the host galaxy. Using these redshift-identified BBH, we show that the Hubble constant is measured at a level of precision better than 1% with advanced detectors like aLIGO at design sensitivity. Since a GW observation is completely independent of other astrophysical means, this qualitatively new probe will help resolve a well-known value discrepancy problem on the Hubble constant from cosmological measurements and local measurements.

The dynamics of bouncing universes is characterized by violating certain coordinate-invariant restrictions on the total energy-momentum tensor, customarily referred to as energy conditions. Although there could be epochs in which the null energy condition is locally violated, it may perhaps be enforced in an averaged sense. Explicit examples of this possibility are investigated in different frameworks.

The effective masses of the neutral mesons in a hadronic medium and under an external magnetic field are evaluated as functions of the baryonic density and the field intensity. For this purpose, the meson polarization is evaluated in the one-loop approximation using a quantum hadrodynamics model which includes $\pi$, $\sigma$, $\omega$, and $\rho$ mesons. The propagators of the baryons include the full effect of the coupling to the magnetic field through their charges and their anomalous magnetic moments. Within the range of magnetic intensities considered here $10^{17}\mathrm{G}<B<{10}^{19}\mathrm{G}$, the dependence on $B$ is moderate for the pion and the longitudinal component of the $\omega$ meson and negligible for the remaining mesons.