Comments on holographic entanglement entropy and RG flows
A bstractUsing holographic entanglement entropy for strip geometry, we construct a candidate for a c-function in arbitrary dimensions. For holographic theories dual to Einstein gravity, this c-function is shown to decrease monotonically along RG flows. A sufficient condition required for this monotonic flow is that the stress tensor of the matter fields driving the holographic RG flow must satisfy the null energy condition over the holographic surface used to calculate the entanglement entropy. In the case where the bulk theory is described by Gauss-Bonnet gravity, the latter condition alone is not sufficient to establish the monotonic flow of the c-function. We also observe that for certain holographic RG flows, the entanglement entropy undergoes a ‘phase transition’ as the size of the system grows and as a result, evolution of the c-function may exhibit a discontinuous drop.

title: Accelerating Bianchi Type-V Cosmology with Perfect Fluid and Heat Flow in Sáez-Ballester Theory
abstract: In this paper we discuss the law of variation of scale factor $a = (t^{k}e^{t})^{\frac{1}{n}}$ which yields a time-dependent deceleration parameter (DP) representing a new class of models that generate a transition of universe from the early decelerated phase to the recent accelerating phase. Exact solutions of Einstein’s modified field equations in Bianchi type-V space-time with perfect fluid and heat conduction are obtained within the framework of Sáez-Ballester scalar-tensor theory of gravitation and the model is found to be in good agreement with recent observations. We find, for n=3,k=1, the present value of DP in derived model as q0=−0.67 which is very near to the observed value of DP at present epoch. We find that the time-dependent DP is sensible for the present day Universe and give an earmark description of evolution of universe. Some physical and geometric properties of the models are also discussed.

title: Quantum corrections to screening at strong coupling
abstract: We compute a certain class of corrections to (specific) screening lengths in strongly coupled non-abelian plasmas using the AdS/CFT correspondence. In this holographic framework, these corrections arise from various higher curvature interactions modifying the leading Einstein gravity action. The changes in the screening lengths are perturbative in inverse powers of the `t Hooft coupling or of the number of colors, as can be made precise in the context where the dual gauge theory is superconformal. We also compare the results of these holographic calculations to lattice results for the analogous screening lengths in QCD. In particular, we apply these results within the program of making quantitative comparisons between the strongly coupled quark-gluon plasma and holographic descriptions of conformal field theory.

title: Entanglement entropy for singular surfaces
abstract: A bstractWe study entanglement entropy for regions with a singular boundary in higher dimensions using the AdS/CFT correspondence and find that various singularities make new universal contributions. When the boundary CFT has an even spacetime dimension, we find that the entanglement entropy of a conical surface contains a term quadratic in the logarithm of the UV cut-off. In four dimensions, the coefficient of this contribution is proportional to the central charge c. A conical singularity in an odd number of spacetime dimensions contributes a term proportional to the logarithm of the UV cut-off. We also study the entanglement entropy for various boundary surfaces with extended singularities. In these cases, similar universal terms may appear depending on the dimension and curvature of the singular locus.

title: Multipoint correlators of conformal field theories: implications for quantum critical transport
abstract: We compute three-point correlators between the stress-energy tensor and con- served currents of conformal field theories (CFTs) in 2+1 dimensions. We first compute the correlators in the large-flavor-number expansion of conformal gauge theories and then do the computation using holography. In the holographic approach, the correlators are computed from an e↵ective action on 3+1 dimensional anti-de Sitter space (AdS4), and depend upon the co-ecient, , of a four-derivative term in the action. We find a precise match between the CFT and the holographic results, thus fixing the values of . The CFTs of free fermions and bosons take the values =1 /12,1/12 respectively, and so saturate the bound | | 1/12 obtained earlier from the holographic theory; the correlator of the conserved gauge flux of U(1) gauge theories takes intermediate values of . The value of also controls the fre- quency dependence of the conductivity, and other properties of quantum-critical transport at non-zero temperatures. Our results for the values of lead to an appealing physical inter- pretation of particle-like or vortex-like transport near quantum phase transitions of interest in condensed matter physics. This paper includes appendices reviewing key features of the AdS/CFT correspondence for condensed matter physicists.

title: Quantum fluctuations of axions
abstract: We study the time evolution of the quantum fluctuations of the axion field for both the QCD axion as well as axions arising in the context of supergravity and string theories. We explicitly keep track not only of the coherently oscillating zero momentum mode of the axion but also of the higher non-zero momentum modes using the full axion potential. The full axion potential makes possible two kinds of instabilities: spinodal instabilities and parametric resonance instabilities. The presence of either of these instabilities can lead to a quasi-exponential increase in the occupation of non-zero momentum modes and the build-up of the quantum fluctuations of the axions. If either of these becomes a significant effect then axions would no longer be a suitable cold dark matter candidate. Our results confirm the conventional wisdom that these effects are not significant in the setting of an expanding FRW universe and hence axions are indeed cold dark matter candidates.

title: Constraints from inflation and reheating on superpartner masses
abstract: Flat directions in the Minimal Supersymmetric Standard Model (MSSM) can become unstable due to radiative corrections, and the global minimum of the (zero temperature) potential can lie at large values of the squark and/or slepton fields. Here we show that, in inflationary models of early cosmology, the universe is very likely to be in the domain of attraction of this global minimum at the end of inflation. While the minimum at the origin of field space is global at sufficiently high temperatures, depending on details of the model, the universe may be trapped in the non-zero minimum until it becomes the global minimum at low temperatures. Parameter values leading to this scenario are therefore ruled out.

title: Gravitational Collapse of Dark Energy Field Configurations
abstract: It is now a well established fact based on several observations that we live in a Universe dominated by dark energy. The most natural candidates for dark energy are fields in curved space-time. We develop the formalism to study the gravitational collapse of fields given any general potential. We apply this formalism to models of dark energy motivated by particle physics considerations. We solve the resulting evolution equations which determine the time evolution of field configurations as well as the dynamics of spacetime.