We discuss a class of critical models in $d\ge 2+1$ dimensions whose electrical conductivity and charge susceptibility are fixed by the central charge in a universal manner. We comment on possible bounds on conductivity, as suggested by holographic duality.

The chiral condensate in QCD at zero temperature does not depend on the quark chemical potential (up to one-third the nucleon mass), whereas the spectral density of the Dirac operator shows a strong dependence on the chemical potential. The cancellations which make this possible also occur on the microscopic scale, where they can be investigated by means of a random matrix model. We show that they can be understood in terms of orthogonality properties of orthogonal polynomials. In the strong non-Hermiticity limit they are related to integrability properties of the spectral density. As a by-product we find exact analytical expressions for the partially quenched chiral condensate in the microscopic domain at nonzero chemical potential.

Action principles of the BF type for diffeomorphism invariant topological field theories living in $n$-dimensional spacetime manifolds are presented. Their construction is inspired by Cuesta and Montesinos’ recent paper where Cartan’s first and second structure equations together with first and second Bianchi identities are treated as the equations of motion for a field theory. In opposition to that paper, the current approach involves also auxiliary fields and holds for arbitrary $n$-dimensional spacetimes. Dirac’s canonical analysis for the actions is detailedly carried out in the generic case and it is shown that these action principles define topological field theories, as mentioned. The current formalism is a generic framework to construct geometric theories with local degrees of freedom by introducing additional constraints on the various fields involved that destroy the topological character of the original theory. The latter idea is implemented in two-dimensional spacetimes where gravity coupled to matter fields is constructed out, which has indeed local excitations.

We consider a compactification with a six-dimensional torus in the type II brane gas models. We show that the dilaton and the scale of each cycle of the internal space are fixed in the presence of NS5-branes and Kaluza-Klein monopoles as well as D-branes with the gauge fields. We can construct various models that lead to fixed moduli by using $T$-duality transformations.

Currently planned second-generation gravitational-wave laser interferometers such as Advanced LIGO exploit the extensively investigated signal-recycling technique. Candidate Advanced LIGO configurations are usually designed to have two resonances within the detection band, around which the sensitivity is enhanced: a stable optical resonance and an unstable optomechanical resonance—which is upshifted from the pendulum frequency due to the so-called optical-spring effect. As an alternative to a feedback control system, we propose an all-optical stabilization scheme, in which a second optical spring is employed, and the test mass is trapped by a stable ponderomotive potential well induced by two carrier light fields whose detunings have opposite signs. The double optical spring also brings additional flexibility in reshaping the noise spectral density and optimizing toward specific gravitational-wave sources. The presented scheme can be extended easily to a multi-optical-spring system that allows further optimization.

We study light scalar mesons in the holographic QCD soft-wall model with a background dilaton field. The masses and decay constants are compatible with experiment and QCD determinations if $a_0(980)$ and $f_0(980)$ are identified as the lightest scalar mesons; moreover, the states are organized in linear Regge trajectories with the same slope of vector mesons. Comparing the two-point correlation function of scalar operators derived on the anti–de Sitter side and in QCD, information about the condensates can be derived. Strong couplings of scalar states to pairs of light pseudoscalar mesons turn out to be small, at odds with experiment and QCD estimates: we discuss how this discrepancy is related to the description of chiral symmetry breaking in this model, and the possible solutions.

We study the charmful three-body baryonic $B$ decays with $D^{(*)}$ or $J/\Psi$ in the final state. We explain the measured rates of ${\overline{B}}^0\to n\overline{p}{D}^{*+}$, ${\overline{B}}^0\to p\overline{p}{D}^{(*)0}$, and $B^{-}\to \Lambda \overline{p}J/\Psi$ and predict the branching fractions of ${\overline{B}}^0\to \Lambda \overline{p}{D}^{*+}$, ${\overline{B}}^0\to {\Sigma }^0\overline{p}{D}^{*+}$, $B^{-}\to \Lambda \overline{p}{D}^0$, and $B^{-}\to \Lambda \overline{p}{D}^{*0}$ to be of order $(1.2,1.1,1.1,3.9)\times {10}^{-5}$, respectively. They are readily accessible to the $B$ factories.

We present an improved QCD light-cone sum rule (LCSR) calculation of the $B\to K$ and $B_s\to K$ form factors by including SU(3)-symmetry breaking corrections. We use recently updated $K$ meson distribution amplitudes which incorporate the complete SU(3)-breaking structure. By applying the method of direct integration in the complex plane, which is presented in detail, the analytical extraction of the imaginary parts of LCSR hard-scattering amplitudes becomes unnecessary and therefore the complexity of the calculation is greatly reduced. The values obtained for the relevant $B_{(s)}\to K$ form factors are as follows: $f_{BK}^{+}(0)={0.36}_{-0.04}^{+0.05}$, $f_{B_{s}K}^{+}(0)={0.30}_{-0.03}^{+0.04}$, and $f_{BK}^T(0)=0.38\pm 0.05$, $f_{B_{s}K}^T(0)=0.30\pm 0.05$. By comparing with the $B\to \pi$ form factors extracted recently by the same method, we find the following SU(3) violation among the $B\to \mathrm{\text{light}}$ form factors: $f_{BK}^{+}(0)/f_{B\pi }^{+}(0)={1.38}_{-0.10}^{+0.11}$, $f_{B_{s}K}^{+}(0)/f_{B\pi }^{+}(0)={1.15}_{-0.09}^{+0.17}$, $f_{BK}^T(0)/f_{B\pi }^T(0)={1.49}_{-0.06}^{+0.18}$, and $f_{B_{s}K}^T(0)/f_{B\pi }^T(0)={1.17}_{-0.11}^{+0.15}$.

We study cosmic Nielsen-Olesen strings in space-times with a positive cosmological constant. For the free cosmic string in a cylindrically symmetric space-time, we calculate the contribution of the cosmological constant to the angle deficit, and to the bending of null geodesics. For a cosmic string in a Schwarzschild–de Sitter space-time, we use Kruskal patches around the inner and outer horizons to show that a thin string can pierce them.

Dark matter (DM) annihilations in the Galaxy may produce high-energy neutrinos, which can be detected by the neutrino telescopes, for example, IceCube, ANTARES, and Super-Kamiokande. The neutrinos can also arise from hadronic interaction between cosmic rays and the atmosphere around the Earth, known as atmospheric neutrino. Current measurements on neutrino flux are consistent with theoretical prediction of atmospheric neutrino within the uncertainties. In this paper, by requiring that the DM annihilation neutrino flux is less than the current measurements, we obtain an upper bound on the cross section of dark matter annihilation $⟨\sigma v⟩$. Compared with previous investigations, we improve the bound by including DM substructure contributions. In our paper, two kinds of substructure effects are scrutinized. One is the substructure average contribution over all directions. The other is the point source effect by a single massive subhalo. We found that the former can improve the bound by several times, while the latter can improve the bound by ${10}^1\sim {10}^4$ utilizing the excellent angular resolution of the neutrino telescope IceCube. The exact improvement depends on the DM profile and the subhalo concentration model. In some models, IceCube can achieve the sensitivity of $⟨\sigma v⟩\sim {10}^{-26}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$.

The canonical quantization in the Weyl gauge of gauge fields in static space-times is presented. With an appropriate definition of transverse and longitudinal components of gauge fields, the Gauss law constraint is resolved explicitly for scalar and spinor QED and a complete nonperturbative solution is given for the quantized Maxwell field coupled to external currents. The formalism is applied in investigations of the electromagnetic field in Rindler spaces. The relation of creation and annihilation operators in Minkowski and Rindler spaces is established, and initial value problems associated with bremsstrahlung of a uniformly accelerated charge are studied. The peculiar scaling properties of scalar and gauge theories in Rindler spaces are discussed, and various quantities such as the photon condensate or the interaction energy of static charges and of scalar sources are computed.

We discuss a variety of bremsstrahlung processes associated with charged particles emitted by evaporating black holes. We show that such particles produce a negligible number of bremsstrahlung photons from their scattering off each other, though at low frequencies inner bremsstrahlung photons dominate over the direct Hawking emission of photons. This analysis and the further analysis of the accompanying paper invalidate Heckler’s claim that sufficiently hot evaporating black holes form QED photospheres and have similar implications for putative QCD photospheres.

Several authors, most notably Heckler, have claimed that the observable Hawking emission from a microscopic black hole is significantly modified by the formation of a photosphere around the black hole due to QED or QCD interactions between the emitted particles. In this paper we analyze these claims and identify a number of physical and geometrical effects which invalidate these scenarios. We point out two key problems. First, the interacting particles must be causally connected to interact, and this condition is satisfied by only a small fraction of the emitted particles close to the black hole. Second, a scattered particle requires a distance $\sim E/m_e^2$ for completing each bremsstrahlung interaction, with the consequence that it is improbable for there to be more than one complete bremsstrahlung interaction per particle near the black hole. These two effects have not been included in previous analyses. We conclude that the emitted particles do not interact sufficiently to form a QED photosphere. Similar arguments apply in the QCD case and prevent a QCD photosphere (chromosphere) from developing when the black hole temperature is much greater than ${\Lambda }_{\mathrm{QCD}}$, the threshold for QCD particle emission. Additional QCD phenomenological arguments rule out the development of a chromosphere around black hole temperatures of order ${\Lambda }_{\mathrm{QCD}}$. In all cases, the observational signatures of a cosmic or Galactic halo background of primordial black holes or an individual black hole remain essentially those of the standard Hawking model, with little change to the detection probability. We also consider the possibility, as proposed by Belyanin et al. and D. Cline et al., that plasma interactions between the emitted particles form a photosphere, and we conclude that this scenario too is not supported.

Gravitational waveforms and fluxes from extreme mass-ratio inspirals can be computed using time-domain methods with accuracy that is fast approaching that of frequency-domain methods. We study in detail the computational efficiency of these methods for equatorial orbits of fast spinning Kerr black holes, and find the number of modes needed in either method—as functions of the orbital parameters—in order to achieve a desired accuracy level. We then estimate the total computation time and argue that for high-eccentricity orbits the time-domain approach may be more efficient computationally. We suggest that in practice low-$m$ modes are computed using the frequency-domain approach, and high-$m$ modes are computed using the time-domain approach, where $m$ is the azimuthal mode number.

Using the Groenewold-Moyal product, the noncommutative Bianchi IX model is constructed by imposing commutation relations on the minisuperspace variables $(\Omega ,{\beta }_{+},{\beta }_{-})$. A noncommutative “wormhole” solution to the corresponding Wheeler-DeWitt equation is constructed and its behavior at fixed $\Omega$ is analyzed.

The interior of a Schwarzschild black hole is investigated at the level of phenomenological dynamics with the discreteness corrections of loop quantum geometry implemented in two different improved quantization schemes. In one scheme, the classical black hole singularity is resolved by the quantum bounce, which bridges the black hole interior with a white hole interior. In the other scheme, the classical singularity is resolved and the event horizon is also diffused by the quantum bounce. Jumping over the quantum bounce, the black hole gives birth to a baby black hole with a much smaller mass. This lineage continues as each classical black hole brings forth its own descendant in the consecutive classical cycle, giving the whole extended spacetime fractal structure, until the solution eventually descends into the deep Planck regime, signaling a breakdown of the semiclassical description. The issues of scaling symmetry and no-hair theorem are also discussed.

In this paper, the equations of motion for geodesics in the neutral rotating black ring metric are derived and the separability of these equations is considered. The bulk of the paper is concerned with sets of solutions where the geodesic equations can be examined analytically—specifically geodesics confined to the axis of rotation, geodesics restricted to the equatorial plane, and geodesics that circle through the center of the ring. The geodesics on the rotational axis behave like a particle in a potential well, while the geodesics confined to the equatorial plane mimic those of the Schwarzschild metric. It is shown that it is impossible to have circular orbits that pass through the ring, but some numerical results are presented which suggest that it is possible to have bound orbits that circle through the ring.

Geometrical and topological properties of the quasiplane Szekeres model and of the plane-symmetric dust model are discussed. Some related comments on the quasihyperbolic model are made. These properties include: (1) The pattern of expansion in the plane-symmetric case, and the Newtonian model that imitates it; (2) The possibility of toroidal topology of the $t=\mathrm{const}$ sections in the plane-symmetric model; (3) The absence of apparent horizons in the quasiplane and quasihyperbolic models (they are globally trapped); (4) Description of the toroidal topology in the Szekeres coordinates; (5) Consequences of toroidal topology in the nonsymmetric quasiplane model; (6) Avoidance of shell crossings in the toroidal model; (7) Interpretation of the mass function in the quasiplane model, with the toroidal and with the infinite space.

A modified-gravity theory is considered with a four-form field strength $F$, a variable gravitational coupling parameter $G(F)$, and a standard matter action. This theory provides a concrete realization of the general vacuum variable $q$ as the four-form amplitude $F$ and allows for a study of its dynamics. The theory gives a flat Friedmann-Robertson-Walker universe with rapid oscillations of the effective vacuum energy density (cosmological “constant”), whose amplitude drops to zero asymptotically. Extrapolating to the present age of the Universe, the order of magnitude of the average vacuum energy density agrees with the observed near-critical vacuum energy density of the present universe. It may even be that this type of oscillating vacuum energy density constitutes a significant part of the so-called cold dark matter in the standard Friedmann-Robertson-Walker framework.