Casimir entropies due to quantum fluctuations in the interaction between electrical bodies can often be negative, caused either by dissipation or by geometry. Although generally such entropies vanish at zero temperature, consistent with the third law of thermodynamics (the Nernst heat theorem), there is a region in the space of temperature and separation between the bodies where negative entropy occurs, while positive interaction entropies arise for large distances or temperatures. Systematic studies on this phenomenon in the Casimir-Polder interaction between a polarizable nanoparticle or atom and a conducting plate in the dipole approximation have been given recently. Since the total entropy should be positive according to the second law of thermodynamics, we expect that the self-entropy of the bodies would be sufficiently positive as to overwhelm the negative interaction entropy. This expectation, however, has not been explicitly verified. Here we compute the self-entropy of an electromagnetic $\delta$-function plate, which corresponds to a perfectly conducting sheet in the strong coupling limit. The transverse electric contribution to the self-entropy is negative, while the transverse magnetic contribution is larger and positive, so the total self-entropy is positive. However, this self-entropy vanishes in the strong-coupling limit. In that case, it is the self-entropy of the nanoparticle, which we recalculate in the perfect conducting limit, that is just sufficient to result in a non-negative total entropy.

We perform a validation of estimates of the growth rate of structure, described by the parameter combination $f{\sigma }_8$, in modified gravity cosmologies. We consider an analysis pipeline based on the redshift-space distortion modeling of the clustering wedges statistic of the galaxy correlation function and apply it to mock catalogues of Lambda cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) and the normal branch of Dvali-Gabadadze-Porrati (DGP) cosmologies. We employ a halo occupation distribution approach to construct our mocks, which we ensure resemble the CMASS sample from Baryon Oscillation Spectroscopic Survey (BOSS) in terms of the total galaxy number density and large-scale amplitude of the power spectrum monopole. We show that the clustering wedges model successfully recovers the true growth rate difference between DGP and $\mathrm{\Lambda }\mathrm{CDM}$, even for cases with over 40% enhancement in $f{\sigma }_8$ compared to $\mathrm{\Lambda }\mathrm{CDM}$. The unbiased performance of the clustering wedges model allows us to use the growth rate values estimated from the BOSS DR12 data to constrain the crossover scale $r_c$ of DGP gravity to ${[r_c{H}_0]}^{-1}<0.97$ ($2\sigma$) or $r_c>3090\mathrm{Mpc}/h$, cutting into the interesting region of parameter space with $r_c\sim H_0^{-1}$ using constraints from the growth of structure alone.

We construct $F(T,{(\nabla T)}^2,\square T)$ gravitational modifications, which are novel classes of modified theories arising from higher-derivative torsional terms in the action and are different than their curvature analogue. Applying them in a cosmological framework, we obtain an effective dark energy sector comprised of the novel torsional contributions. We perform a detailed dynamical analysis for two specific examples, extracting the stable late-time solutions and calculating the corresponding observables. We show that the thermal history of the Universe can be reproduced, and it can result in a dark-energy-dominated, accelerating universe, where the dark-energy equation-of-state parameter lies in the quintessence regime, or may exhibit the phantom-divide crossing during the cosmological evolution. Finally, the scale factor behaves asymptotically, either as a power law or as an exponential, in agreement with observations.

Energy is at best defined quasilocally in general relativity. Quasilocal energy definitions depend on the conditions one imposes on the boundary Hamiltonian, i.e., how a finite region of spacetime is “isolated.” Here, we propose a method to define and investigate systems in terms of their matter plus gravitational energy content. We adopt a generic construction, that involves embedding of an arbitrary dimensional world sheet into an arbitrary dimensional spacetime, to a $2+2$ picture. In our case, the closed 2-dimensional spacelike surface $\mathbb{S}$, that is orthogonal to the 2-dimensional timelike world sheet $\mathbb{T}$ at every point, encloses the system in question. The integrability conditions of $\mathbb{T}$ and $\mathbb{S}$ correspond to three null tetrad gauge conditions once we transform our notation to the one of the null cone observables. We interpret the Raychaudhuri equation of $\mathbb{T}$ as a work-energy relation for systems that are not in equilibrium with their surroundings. We achieve this by identifying the quasilocal charge densities corresponding to rotational and nonrotational degrees of freedom, in addition to a relative work density associated with tidal fields. We define the corresponding quasilocal charges that appear in our work-energy relation and which can potentially be exchanged with the surroundings. These charges and our tetrad conditions are invariant under type-III Lorentz transformations, i.e., the boosting of the observers in the directions orthogonal to $\mathbb{S}$. We apply our construction to a radiating Vaidya spacetime, a $C$-metric and the interior of a Lanczos-van Stockum dust metric. The delicate issues related to the axially symmetric stationary spacetimes and possible extensions to the Kerr geometry are also discussed.

In this paper we perform a systematic study of spatially flat $[(3+\mathrm{D})+1]$-dimensional Einstein-Gauss-Bonnet cosmological models with the $\mathrm{\Lambda }$-term. We consider models that topologically are the product of two flat isotropic subspaces with different scale factors. One of these subspaces is three-dimensional and represents our space and the other is $D$-dimensional and represents extra dimensions. We consider no Ansatz on the scale factors, which makes our results quite general. With both Einstein-Hilbert and Gauss-Bonnet contributions in play, the cases with $D=1$ and $D=2$ have different dynamics due to the different structure of the equations of motion. We analytically study equations of motion in both cases and describe all possible regimes. It is demonstrated that the $D=1$ case does not have physically viable regimes while $D=2$ has a smooth transition from high-energy Kasner to an anisotropic exponential regime. This transition occurs for two ranges of $\alpha$ and $\mathrm{\Lambda }$: $\alpha >0$ with $\alpha \mathrm{\Lambda }\le 1/2$ (including $\mathrm{\Lambda }<0$) and $\alpha <0$, $\mathrm{\Lambda }>0$ with $\alpha \mathrm{\Lambda }<-3/2$. For the latter case, if $\alpha \mathrm{\Lambda }=-3/2$, the extra-dimensional part has $h\to 0$ and so the size of extra dimensions (in the sense of the scale factor) is reaching a constant value. We report substantial differences between $D=1$ and $D=2$ cases and between these cases and their vacuum counterparts, describe features of the cases under study, and discuss the origin of the differences.

We solve the Laplace equation $\square h_{ij}=0$ describing the propagation of gravitational waves in an expanding background metric with a power law scale factor in the presence of a point mass in the weak-field approximation (Newtonian McVittie background). We use boundary conditions at large distances from the mass corresponding to a standing spherical gravitational wave in an expanding background which is equivalent to a linear combination of an incoming and an outgoing propagating gravitational wave. We compare the solution with the corresponding solution in the absence of the point mass and show that the point mass increases the amplitude of the wave and also decreases its frequency (as observed by an observer at infinity) in accordance with gravitational time delay.

We analytically study the linear response of a near-extremal Kerr black hole to external scalar, electromagnetic, and gravitational field perturbations. We show that the energy density, electromagnetic field strength, and tidal force experienced by infalling observers exhibit transient growth near the horizon. The growth lasts arbitrarily long in the extremal limit, reproducing the horizon instability of extremal Kerr. We explain these results in terms of near-horizon geometry and discuss potential astrophysical implications.

The relativistic dynamic equations are derived for a superfluid-superconducting mixture coupled to an electromagnetic field. For definiteness, and bearing in mind possible applications of our results to neutron stars, it is assumed that the mixture is composed of superfluid neutrons, superconducting protons, and normal electrons. We analyze the proton superconductivity of both types I and II and allow for the possible presence of neutron and proton vortices (or magnetic domains in the case of type-I proton superconductivity). The derived equations neglect all dissipative effects except for the mutual friction dissipation and are valid for arbitrary temperatures (i.e., they do not imply that all nucleons are paired), which is especially important for magnetar conditions. It is demonstrated that these general equations can be substantially simplified for typical neutron stars, for which a kind of magnetohydrodynamic approximation is justified. Our results are compared to the nonrelativistic formulations existing in the literature, and a number of discrepancies are found. In particular, it is shown that, generally, the electric displacement $\mathit{D}$ does not coincide with the electric field $\mathit{E}$, contrary to what is stated in previous works. The relativistic framework developed here is easily extendable to account for more sophisticated microphysics models, and it provides the necessary basis for realistic modeling of neutron stars.

Axions can be described by a relativistic field theory with a real scalar field ϕ whose self-interaction potential is a periodic function of $\varphi$. Low-energy axions, such as those produced in the early Universe by the vacuum misalignment mechanism, can be described more simply by a nonrelativistic effective field theory with a complex scalar field $\psi$ whose effective potential is a function of ${\psi }^{*}\psi$. We determine the coefficients in the expansion of the effective potential to fifth order in ${\psi }^{*}\psi$ by matching low-energy axion scattering amplitudes. In order to describe a Bose-Einstein condensate of axions that is too dense to truncate the expansion of the effective potential in powers of ${\psi }^{*}\psi$, we develop a sequence of systematically improvable approximations to the effective potential that resum terms of all orders in ${\psi }^{*}\psi$.

The deconfinement transition and the hadronization mechanism at high energy are related to the quark-antiquark string breaking, and the corresponding temperature depends on the string tension $\sigma$. In the Unruh scheme of hadron production, it turns out $T=\sqrt{\sigma /2\pi }$, with $\sigma \simeq {\epsilon }^{\mathrm{vac}}$, the vacuum energy density. In heavy ion collisions at lower energy, i.e., large baryonchemical potential, ${\mu }_B$, the dynamics is dominated by Fermi statistics and baryon repulsion. However, one can still consider ${\epsilon }^{\mathrm{vac}}$ as the relevant physical scale, and its evaluation as a function of the baryon density, in a nuclear matter approach, gives dynamical information on the ${\mu }_B$ dependence of the hadronization temperature and on the value of the critical end point in the $T-{\mu }_B$ plane.

Spontaneously broken supersymmetry (SUSY) and a vanishingly small cosmological constant imply that $R$ symmetry must be spontaneously broken at low energies. Based on this observation, we suppose that, in the sector responsible for low-energy $R$ symmetry breaking, a discrete $R$ symmetry remains preserved at high energies and only becomes dynamically broken at relatively late times in the cosmological evolution, i.e., after the dynamical breaking of SUSY. Prior to $R$ symmetry breaking, the Universe is then bound to be in a quasi–de Sitter phase—which offers a dynamical explanation for the occurrence of cosmic inflation. This scenario yields a new perspective on the interplay between SUSY breaking and inflation, which neatly fits into the paradigm of high-scale SUSY: inflation is driven by the SUSY-breaking vacuum energy density, while the chiral field responsible for SUSY breaking, the Polonyi field, serves as the inflaton. Because $R$ symmetry is broken only after inflation, slow-roll inflation is not spoiled by otherwise dangerous gravitational corrections in supergravity. We illustrate our idea by means of a concrete example, in which both SUSY and $R$ symmetry are broken by strong gauge dynamics and in which late-time $R$ symmetry breaking is triggered by a small inflaton field value. In this model, the scales of inflation and SUSY breaking are unified, the inflationary predictions are similar to those of F-term hybrid inflation in supergravity, reheating proceeds via gravitino decay at temperatures consistent with thermal leptogenesis, and the sparticle mass spectrum follows from pure gravity mediation. Dark matter consists of thermally produced winos with a mass in the TeV range.

We consider the $HZ$ associated production at the 14 TeV LHC in the littlest Higgs model (LHM) and study the corrections of the transverse momentum resummation and threshold resummation at the next-to-leading logarithmic (NLL) accuracy and the fixed-order prediction at the QCD next-to-leading order (NLO) including the contribution from the one-loop-induced $gg$-fusion channel. The QCD $\mathrm{NLO}+\mathrm{NLL}$ effects on the integrated cross section and the distributions of transverse momentum and invariant mass of the $HZ$ system for the $HZ$ production in the LHM are discussed. The distributions of transverse momentum and invariant mass of the $HZ$ system are evaluated by means of the transverse momentum resummation and threshold resummation, respectively. We estimate their scale uncertainties and find that the predictions obtained at the QCD $\mathrm{NLO}+\mathrm{NLL}$ accuracy are much more reliable than those using the pure NLO approach. We see also that the relative deviation between the results in the LHM and the standard model is considerably reduced by the resummation effects, but still observable.

We present the CoLoRFulNNLO method to compute higher order radiative corrections to jet cross sections in perturbative QCD. We apply our method to the computation of event shape observables in electron-positron collisions at NNLO accuracy and validate our code by comparing our predictions to previous results in the literature. We also calculate for the first time jet cone energy fraction at NNLO.

We use an anti–de Sitter/quantum chromodynamics holographic light-front wave function for the $\rho$ and $\varphi$ mesons, in conjunction with the color glass condensate dipole cross section whose parameters are fitted to the most recent 2015 high precision HERA data on inclusive deep inelastic scattering, in order to predict the cross sections for diffractive $\rho$ and $\varphi$ electroproduction. Our results suggest that the holographic meson light-front wave function is able to give a simultaneous description of $\rho$ and $\varphi$ production data provided we use a set of light quark masses with $m_{u,d}<m_s\approx 0.14\mathrm{GeV}$.

By adopting the nonlinear realization of chiral symmetry, a holographic model for the baryon octet is proposed. The mass spectra of the baryon octet and their low-lying excited states, which show good consistency with experiments, are calculated. The couplings of pion to nucleons are derived in two gauges and are shown to be equivalent with each other. It also shows that only derivative couplings of pion to nucleons appear in this holographic model. The coupling constant is then calculated.

We discuss the parameter space reach of future experiments searching for heavy neutral leptons (HNLs). We consider the GeV seesaw model with three HNL generations and focus on two classes of models: generic assumptions (such as random mass matrices or the Casas-Ibarra parametrization) and flavor symmetry-generated models. We demonstrate that the generic approaches lead to comparable parameter space predictions, which tend to be at least partially within the reach of future experiments. On the other hand, specific flavor symmetry models yield more refined predictions, and some of these can be more clearly excluded. We also highlight the importance of measuring the flavor-dependent couplings of the HNLs as a model discriminator, and we clarify the impact of assumptions frequently used in the literature to show the parameter space reach for the active-sterile mixings.

Hydroxide catalysis bonds are low mechanical loss joints which are used in the fused silica mirror suspensions of current room temperature interferometric gravitational wave detectors, one of the techniques which was essential to allow the recent detection of gravitational radiation by LIGO. More sensitive detectors may require cryogenic techniques with sapphire as a candidate mirror and suspension material, and thus hydroxide catalysis bonds are under consideration for jointing sapphire. This paper presents the first measurements of the mechanical loss of such a bond created between sapphire substrates and measured down to cryogenic temperatures. The mechanical loss is found to be $0.03\pm 0.01$ at room temperature, decreasing to $(3\pm 1)\times 10^{-4}$ at 20 K. The resulting thermal noise of the bonds on several possible mirror suspensions is presented.

Using $482{\mathrm{pb}}^{-1}$ of $e^{+}{e}^{-}$ collision data collected at a center-of-mass energy of $\sqrt{s}=4.009\mathrm{GeV}$ with the BESIII detector, we measure the branching fractions of the decays $D_s^{+}\to {\mu }^{+}{\nu }_{\mu }$ and $D_s^{+}\to {\tau }^{+}{\nu }_{\tau }$. By constraining the ratio of decay rates of $D_s^{+}$ to ${\tau }^{+}{\nu }_{\tau }$ and to ${\mu }^{+}{\nu }_{\mu }$ to the Standard Model prediction, the branching fractions are determined to be $\mathcal{B}(D_s^{+}\to {\mu }^{+}{\nu }_{\mu })=(0.495\pm 0.067\pm 0.026)\%$ and $\mathcal{B}(D_s^{+}\to {\tau }^{+}{\nu }_{\tau })=(4.83\pm 0.65\pm 0.26)\%$. Using these branching fractions, we obtain a value for the decay constant $f_{D_s^{+}}$ of $(241.0\pm 16.3\pm 6.5)\mathrm{MeV}$, where the first error is statistical and the second systematic.

The cross section for pair production of top quarks ($t\overline{t}$) with high transverse momenta is measured in $pp$ collisions, collected with the CMS detector at the LHC with $\sqrt{s}=8\mathrm{TeV}$ in data corresponding to an integrated luminosity of $19.7{\mathrm{fb}}^{-1}$. The measurement is performed using $\mathrm{lepton}+\text{jets}$ events, where one top quark decays semileptonically, while the second top quark decays to a hadronic final state. The hadronic decay is reconstructed as a single, large-radius jet, and identified as a top quark candidate using jet substructure techniques. The integrated cross section and the differential cross sections as a function of top quark $p_{\mathrm{T}}$ and rapidity are measured at particle level within a fiducial region related to the detector-level requirements and at parton level. The particle-level integrated cross section is found to be ${\sigma }_{t\overline{t}}=0.499\pm 0.035(\mathrm{stat}+\mathrm{syst})\pm 0.095(\mathrm{theo})\pm 0.013(\mathrm{lumi})\mathrm{pb}$ for top quark $p_{\mathrm{T}}>400\mathrm{GeV}$. The parton-level measurement is ${\sigma }_{t\overline{t}}=1.44\pm 0.10(\mathrm{stat}+\mathrm{syst})\pm 0.29(\mathrm{theo})\pm 0.04(\mathrm{lumi})\mathrm{pb}$. The integrated and differential cross section results are compared to predictions from several event generators.

The interferometric LIGO detectors have recently measured the first direct gravitational-wave signal from what has been interpreted as the inspiral, merger and ringdown of a binary system of black holes. The signal-to-noise ratio of the measured signal is large enough to leave little doubt that it does refer to the inspiral of two massive and ultracompact objects, whose merger yields a rotating black hole. Yet, the quality of the data is such that some room is left for alternative interpretations that do not involve black holes, but other objects that, within classical general relativity, can be equally massive and compact, namely, gravastars. We here consider the hypothesis that the merging objects were indeed gravastars and explore whether the merged object could therefore be not a black hole but a rotating gravastar. After comparing the real and imaginary parts of the ringdown signal of GW150914 with the corresponding quantities for a variety of gravastars, and notwithstanding the very limited knowledge of the perturbative response of rotating gravastars, we conclude it is not possible to model the measured ringdown of GW150914 as due to a rotating gravastar.