We study the shear viscosity to entropy ratio $\eta /S$ in the boundary field theories dual to black-hole backgrounds in theories of gravity coupled to a scalar field, and generalizations including a Maxwell field and nonminimal scalar couplings. Motivated by the observation in simple examples that the saturation of the $\eta /S\ge 1/(4\pi )$ bound is correlated with the existence of a generalized Smarr relation for the planar black-hole solutions, we investigate this in detail for the general black-hole solutions in these theories, focusing especially on the cases where the scalar field plays a nontrivial role and gives rise to an additional parameter in the space of solutions. We find that a generalized Smarr relation holds in all cases, and in fact it can be viewed as the bulk gravity dual of the statement of the saturation of the viscosity to entropy bound. We obtain the generalized Smarr relation, whose existence depends upon a scaling symmetry of the planar black-hole solutions, by two different but related methods, one based on integrating the first law of thermodynamics, and the other based on the construction of a conserved Noether charge.

In this paper, we explore the interior dynamics of neutral and charged black holes. Scalar collapses in flat, Schwarzschild, and Reissner-Nordström background geometries are simulated. We examine the dynamics in the vicinities of the central singularity of a Schwarzschild black hole and of the inner horizon of a Reissner-Nordström black hole. In simulating scalar collapses in Schwarzschild and Reissner-Nordström geometries, Kruskal and Kruskal-like coordinates are used, respectively, with the presence of a scalar field being taken into account. It is found that, besides near the inner horizons of Reissner-Nordström and Kerr black holes, mass inflation also takes place near the central singularity in neutral scalar collapse. Approximate analytic expressions for different types of mass inflation are partially obtained via a close interplay between numerical and analytical approaches and an examination of the connections between Schwarzschild black holes, Reissner-Nordström black holes, neutral collapse, and charge scattering. We argue that the mass inflations near the central singularity and the inner horizon are related to the localness of the dynamics in strong gravity regions. This is in accord with the Belinskii, Khalatnikov, and Lifshitz conjecture.

We investigate the thermodynamic equilibrium states of a rotating thin shell, i.e., a ring, in a ($2+1$)-dimensional spacetime with a negative cosmological constant. The inner and outer regions with respect to the shell are given by the vacuum anti-de Sitter and the rotating Bañados-Teitelbom-Zanelli spacetimes, respectively. The first law of thermodynamics on the thin shell, together with three equations of state for the pressure, the local inverse temperature and the thermodynamic angular velocity of the shell, yields the entropy of the shell, which is shown to depend only on its gravitational radii. When the shell is pushed to its own gravitational radius and its temperature is taken to be the Hawking temperature of the corresponding black hole, the entropy of the shell coincides with the Bekenstein-Hawking entropy. In addition, we consider simple ansätze for the equations of state, as well as a power-law equation of state where the entropy and the thermodynamic stability conditions can be examined analytically.

The universal coupling of matter and gravity is one of the most important features of general relativity. In quantum gravity, in particular spin foams, matter couplings have been defined in the past, yet the mutual dynamics, in particular if matter and gravity are strongly coupled, are hardly explored, which is related to the definition of both matter and gravitational degrees of freedom on the discretization. However, extracting these mutual dynamics is crucial in testing the viability of the spin foam approach and also establishing connections to other discrete approaches such as lattice gauge theories. Therefore, we introduce a simple two-dimensional toy model for Yang-Mills coupled to spin foams, namely an Ising model coupled to so-called intertwiner models defined for $\mathrm{SU}(2{)}_k$. The two systems are coupled by choosing the Ising coupling constant to depend on spin labels of the background, as these are interpreted as the edge lengths of the discretization. We coarse grain this toy model via tensor network renormalization and uncover an interesting dynamics: the Ising phase transition temperature turns out to be sensitive to the background configurations and conversely, the Ising model can induce phase transitions in the background. Moreover, we observe a strong coupling of both systems if close to both phase transitions.

We investigate the production and freeze-out of dark matter with a constant thermally averaged cross section in a generic bouncing-universe framework. Our result shows that there is a novel avenue in which dark matter is produced thermally and has a weak freezing-out process; this is in addition to two previously known cases, the case with thermal production and strong freezing out case and the case with nonthermal production and weak freezing out, in which the relic abundance of dark matter is inverse and proportional to its cross section, respectively. We calculated the relic abundance of dark matter for this new case and find that it is independent of its cross section. We also present the cosmological constraints on the cross section and mass relation of dark matter for this new case by utilizing the observational data of the matter-energy density fraction.

We present a detailed analysis of the expected signal-to-noise ratios of supermassive black hole binaries on eccentric orbits observed by pulsar timing arrays. We derive several analytical relations that extend the results of Peters and Mathews [Phys. Rev. D 131, 435 (1963)] to quantify the impact of eccentricity in the detection of single resolvable binaries in the pulsar timing array band. We present ready-to-use expressions to compute the increase/loss in signal-to-noise ratio of eccentric single resolvable sources whose dominant harmonic is located in the low/high frequency sensitivity regime of pulsar timing arrays. Building upon the work of Phinney (arXiv:astro-ph/0108028) and Enoki and Nagashima [Prog. Theor. Phys. 117, 241 (2007)], we present an analytical framework that enables the construction of rapid spectra for a stochastic gravitational-wave background generated by a cosmological population of eccentric sources. We confirm previous findings which indicate that, relative to a population of quasicircular binaries, the strain of a stochastic, isotropic gravitational-wave background generated by a cosmological population of eccentric binaries will be suppressed in the frequency band of pulsar timing arrays. We quantify this effect in terms of signal-to-noise ratios in a pulsar timing array.

We study the oscillations of relativistic stars, incorporating key physics associated with internal composition, thermal gradients and crust elasticity. Our aim is to develop a formalism which is able to account for the state-of-the-art understanding of the complex physics associated with these systems. As a first step, we build models using a modern equation of state including composition gradients and density discontinuities associated with internal phase transitions (like the crust-core transition and the point where muons first appear in the core). In order to understand the nature of the oscillation spectrum, we carry out cooling simulations to provide realistic snapshots of the temperature distribution in the interior as the star evolves through adolescence. The associated thermal pressure is incorporated in the perturbation analysis, and we discuss the presence of $g$-modes arising as a result of thermal effects. We also consider interface modes due to phase-transitions and the gradual formation of the star’s crust and the emergence of a set of shear modes.

Full-sky maps of the cosmic microwave background temperature reveal a 7% asymmetry of fluctuation power between two halves of the sky. A common phenomenological model for this asymmetry is an overall dipole modulation of statistically isotropic fluctuations, which produces particular off-diagonal correlations between multipole coefficients. We compute these correlations and construct corresponding estimators for the amplitude and direction of the dipole modulation. Applying these estimators to various cut-sky temperature maps from Planck and WMAP data shows consistency with a dipole modulation, differing from a null signal at $2.5\sigma$, with an amplitude and direction consistent with previous fits based on the temperature fluctuation power. The signal is scale dependent, with a statistically significant amplitude at angular scales larger than 2°. Future measurements of microwave background polarization and gravitational lensing can increase the significance of the signal. If the signal is not a statistical fluke in an isotropic universe, it requires new physics beyond the standard model of cosmology.

Thermal noise resulting from the mechanical loss of multilayer dielectric coatings is expected to impose a limit to the sensitivities of precision measurement systems used in fundamental and applied science. In the case of gravitational wave astronomy, future interferometric gravitational wave detectors are likely to operate at cryogenic temperatures to reduce such thermal noise and ameliorate thermal loading effects, with the desirable thermomechanical properties of silicon making it an attractive mirror substrate choice for this purpose. For use in such a precision instrument, appropriate coatings of low thermal noise are essential. Amorphous silicon ($a\text{−}\mathrm{Si}$) deposited by e-beam and other techniques has been shown to have low mechanical loss. However, to date, the levels of mechanical and optical loss for $a\text{−}\mathrm{Si}$ when deposited by ion-beam sputtering (the technique required to produce amorphous mirrors of the specification for gravitational wave detector mirrors) are unknown. In this paper results from measurements of the mechanical loss of a series of IBS $a\text{−}\mathrm{Si}$ films are presented which show that reductions are possible in coating thermal noise of a factor of 1.5 at 120 K and 2.1 at 20 K over the current best IBS coatings (alternating stacks of silica and titania-doped tantala), with further reductions feasible under appropriate heat treatments.

We investigate the inner structure of a general $SU(2)$ [naturally including $SO(3)$] symmetry system—the fermion-gauge field interaction system—and achieve naturally a set of gauge-invariant spin and orbital angular momentum operators of fermion and gauge fields by Noether’s theorem in general field theory. Some new relations concerning non-Abelian field strengths are discovered, e.g., the covariant transverse condition, covariant parallel condition (i.e., non-Abelian divergence, non-Abelian curl), and simplified $SU(2)$ Coulomb theorem. And we show that the condition that Chen et al. obtained to construct their gauge-invariant angular momentum operators is a result of some fundamental equations in the general field theory. The results obtained in this paper present a new perspective for looking at the overall structure of the gauge field, and provide a new viewpoint to the final resolution of the nucleon spin crisis in the general field theory. Especially, the achieved theory in this paper can calculate the strong interactions with isospin symmetry and solves the serious problem without gauge-invariant angular momenta in strong interaction systems with isospin symmetry, and then the achieved predictions in the calculations can be exactly measured by particle physics experiments due to their gauge invariant properties.

We study the discovery prospects of a heavy neutral scalar arising from a $U(1{)}_{B-L}$ extension of the Standard Model (SM) during the Large Hadron Collider’s high luminosity runs (HL-LHC). This heavy neutral scalar mixes with the SM Higgs boson through a Higgs portal and interacts with the SM particles with an interaction strength proportional to the sine of the mixing angle. The mixing between the two Higgs bosons is constrained by direct and indirect measurements. We choose an experimentally viable mixing angle and explore in detail the $ZZ$ and $WW$ decay modes of the heavy Higgs boson. For the $ZZ$ case, we focus on the cleanest $4\ell$ and $2\ell 2j$ final states and find that a heavy Higgs boson of mass smaller than 500 GeV can be discovered at the HL-LHC. For the $WW$ decay mode, we analyze the $\ell jj{\cancel{E}}_T$ signature. We implement novel background reduction techniques in order to tackle the huge background by performing both cut-based and multivariate analyses. However, large backgrounds render this channel challenging. We briefly discuss the discovery prospects of the heavy $Z^{\prime }$-boson arising in this model.

We study a type I seesaw model of neutrino masses within the framework of $A_4$ flavor symmetry. Incorporating the presence of both singlet and triplet flavons under $A_4$ symmetry, we construct the leptonic mass matrices involved in the type I seesaw mechanism. We then construct the light neutrino mass matrix using the $3\sigma$ values of neutrino oscillation parameters keeping the presently undetermined parameters, namely, the lightest neutrino mass $m_{\text{lightest}}$, one Dirac CP phase $\delta$, and two Majorana phases $\alpha ,\beta$, as free parameters. Comparing the mass matrices derived using $A_4$ parameters as well as light neutrino parameters, we then evaluate all the $A_4$ parameters in terms of light neutrino parameters. Assuming some specific vacuum alignments of the $A_4$ triplet flavon field, we then numerically evaluate all the free parameters in the light neutrino sector, using them to find out the remaining $A_4$ parameters. We then use the numerical values of these parameters to calculate baryon asymmetry through the mechanism of leptogenesis. We constrain not only the $A_4$ vacuum alignments from the requirement of successful leptogenesis, but also the free parameters in the light neutrino sector $(m_{\text{lightest}},\delta ,\alpha ,\beta )$ to a certain range of values. These values can be tested in ongoing and future neutrino experiments, providing a way to discriminate between different possible $A_4$ vacuum alignments discussed in this work.

We determine the curvature of the pseudocritical line of strong interactions by means of numerical simulations at imaginary chemical potentials. We consider $N_f=2+1$ stout improved staggered fermions with physical quark masses and the tree level Symanzik gauge action, and explore four different sets of lattice spacings, corresponding to $N_t=6,8,10,12$, in order to extrapolate results to the continuum limit. Our final estimate is $\kappa =0.0135(20)$.

We present an analytical next-to-leading-order QCD calculation of the partonic cross sections for the process $pp\to (\text{jet}h)X$, for which a specific hadron is observed inside a fully reconstructed jet. In order to obtain the analytical results, we assume the jet to be relatively narrow. We show that the results can be cast into a simple and systematic form based on suitable universal jet functions for the process. We confirm the validity of our calculation by comparing to previous results in the literature for which the next-to-leading-order cross section was treated entirely numerically by Monte Carlo integration techniques. We present phenomenological results for experiments at the LHC and at RHIC. These suggest that $pp\to (\text{jet}h)X$ should enable very sensitive probes of fragmentation functions, especially of the one for gluons.

We investigate the influence of a homogeneous and constant strong external magnetic field on the heavy-meson spectrum. Quarkonium states $c\overline{c}$ and $b\overline{b}$ are described within a nonrelativistic framework and by means of a suitable potential model based on the Cornell parametrization. In particular, in this work we propose a model which takes into account the possible anisotropies emerging at the level of the static quark-antiquark potential, as observed in recent lattice studies. The investigation is performed both with and without taking into account the anisotropy of the static potential, in order to better clarify its effects.

LHCb has reported deviations from the Standard Model in $b\to s{\mu }^{+}{\mu }^{-}$ transitions for which a new neutral gauge boson is a prime candidate for an explanation. As this gauge boson has to couple in a flavor nonuniversal way to muons and electrons in order to explain $R_K$, it is interesting to examine the possibility that also lepton flavor is violated, especially in the light of the CMS excess in $h\to {\tau }^{\pm }{\mu }^{\mp }$. In this article, we investigate the perspectives to discover the lepton-flavor violating modes $B\to K^{(*)}{\tau }^{\pm }{\mu }^{\mp }$, $B_s\to {\tau }^{\pm }{\mu }^{\mp }$ and $B\to K^{(*)}{\mu }^{\pm }{e}^{\mp }$, $B_s\to {\mu }^{\pm }{e}^{\mp }$. For this purpose we consider a simplified model in which new-physics effects originate from an additional neutral gauge boson ($Z^{\prime }$) with generic couplings to quarks and leptons. The constraints from $\tau \to 3\mu$, $\tau \to \mu \nu \overline{\nu }$, $\mu \to e\gamma$, $g_{\mu }-2$, semileptonic $b\to s{\mu }^{+}{\mu }^{-}$ decays, $B\to K^{(*)}\nu \overline{\nu }$ and $B_s$–${\overline{B}}_s$ mixing are examined. From these decays, we determine upper bounds on the decay rates of lepton-flavor violating $B$ decays. $\mathrm{Br}(B\to K\nu \overline{\nu })$ limits the branching ratios of lepton-flavor violating $B$ decays to be smaller than $8\times {10}^{-5}(2\times {10}^{-5})$ for vectorial (left-handed) lepton couplings. However, much stronger bounds can be obtained by a combined analysis of $B_s$–${\overline{B}}_s$, $\tau \to 3\mu$, $\tau \to \mu \nu \overline{\nu }$ and other rare decays. The bounds depend on the amount of fine-tuning among the contributions to $B_s$–${\overline{B}}_s$ mixing. Allowing for a fine-tuning at the percent level we find upper bounds of the order of ${10}^{-6}$ for branching ratios into $\tau \mu$ final states, while $B_s\to {\mu }^{\pm }{e}^{\mp }$ is strongly suppressed and only $B\to K^{(*)}{\mu }^{\pm }{e}^{\mp }$ can be experimentally accessible (with a branching ratio of order ${10}^{-7}$).

The one-loop quantum effective action $W$ of the scalar field “living” on the AdS background of the Randall-Sundrum (RS) model has been defined by a now-popular way which excludes bulk UV divergencies; thus, the induced Planck mass is given not by the UV regularization parameter like in Sakharov’s pioneer work but by the location of the UV cut of AdS space. Resummation of the Schwinger-DeWitt expansion of the action $W$ is performed by the novel “auxiliary mass” method. The inverse mass squared parameter of this expansion is determined by the location of the “visible” IR brane of the RS model. The obtained expression for the induced vacuum energy density coincides with the independently calculated VEV of the stress-energy tensor; the corresponding potential in four dimensions possesses a nontrivial extremum which hopefully will permit us to stabilize the IR brane and hence to fix the observed small value of the mass hierarchy in analogy with the Coleman-Weinberg mechanism. It is demonstrated that naive equating of values of the induced Planck mass and vacuum energy density to those of the RS model determines otherwise arbitrary constants of the model. A principle of quantum self-consistency generalizing this approach is proposed.

Asymptotic freedom of gluons in pure-gauge QCD is obtained in the leading terms of their renormalized Hamiltonian in the Fock space, instead of considering virtual Green’s functions or scattering amplitudes. Namely, we calculate the three-gluon interaction term in the effective front-form Hamiltonian for gluons in the Minkowski space-time using the renormalization group procedure for effective particles (RGPEP), with a new generator. The resulting three-gluon vertex is a function of the scale parameter, $s$, that has an interpretation of the size of effective gluons. The corresponding Hamiltonian running coupling constant, $g_{\lambda }$, depending on the associated momentum scale $\lambda =1/s$, is calculated in the series expansion in powers of $g_0=g_{{\lambda }_0}$ up to the terms of third order, assuming some small value for $g_0$ at some large ${\lambda }_0$. The result exhibits the same finite sensitivity to small-$x$ regularization as the one obtained in an earlier RGPEP calculation, but the new calculation is simpler than the earlier one because of a simpler generator. This result establishes a degree of universality for pure-gauge QCD in the RGPEP.

The standard noise model in gravitational wave (GW) data analysis assumes detector noise is stationary and Gaussian distributed, with a known power spectral density (PSD) that is usually estimated using clean off-source data. Real GW data often depart from these assumptions, and misspecified parametric models of the PSD could result in misleading inferences. We propose a Bayesian semiparametric approach to improve this. We use a nonparametric Bernstein polynomial prior on the PSD, with weights attained via a Dirichlet process distribution, and update this using the Whittle likelihood. Posterior samples are obtained using a blocked Metropolis-within-Gibbs sampler. We simultaneously estimate the reconstruction parameters of a rotating core collapse supernova GW burst that has been embedded in simulated Advanced LIGO noise. We also discuss an approach to deal with nonstationary data by breaking longer data streams into smaller and locally stationary components.