119598948
Asymptotic analysis of the Boltzmann equation for dark matter relics
This paper presents an asymptotic analysis of the Boltzmann equations (Riccati differential equations) that describe the physics of thermal dark-matter-relic abundances. Two different asymptotic techniques are used, boundary-layer theory, which makes use of asymptotic matching, and the delta expansion, which is a powerful technique for solving nonlinear differential equations. Two different Boltzmann equations are considered. The first is derived from general relativistic considerations and the second arises in dilatonic string cosmology. The global asymptotic analysis presented here is used to find the long-time behavior of the solutions to these equations. In the first case, the nature of the so-called freeze-out region and the post-freeze-out behavior is explored. In the second case, the effect of the dilaton on cold dark-matter abundances is calculated and it is shown that there is a large-time power-law fall off of the dark-matter abundance.
8253414
The omega effect for neutral mesons
The possible role of decoherence due to space-time foam is discussed within the context of two models, one based on string/brane theory. and the other based on properties of black hole horizons in general relativity. It is argued that the density matrix satisfies a dissipative master equation, primarily from the study of renormalization group flows in non-critical string theory. This interpretation of the zero mode of the Liouville field as time leads necessarily to the CPT operator being ill defined. One striking consequence is that the quantum mechanical correlations of pair states of neutral mesons produced in meson factories are changed from the usual EPR state. The magnitude of this departure from EPR correlations is characterised by a parameter ω. The predicted value of ω is very small or zero. However it is shown explicitly that the the non-vanishing of ω is only a feature of the model based on string/brane theory.
120565281
Frustration and dynamics
Dynamical models incorporating frustration are discussed in general. In particular, it is shown how self-screening of Yang-Mills fields may lead to models of a generalized Ma-Rudnick genre for the spin-glass.
120412772
Renormalization-group approach to the lattice massive Schwinger model
Using Migdal-type recursion relations, the long-distance Coulomb force is found to be screened in the massive Schwinger model on a lattice. (AIP)
115620347
The Schwinger mechanisms in non-abelian gauge theories
Abstract An alternative to the Higgs-Kibble mechanism for the formulation of spontaneously broken gauge theories has been recently proposed. It is shown how the new procedures can be generalised to the case when non-Abelian gauge groups are present.
123114677
Mixing of operators in Wilson expansions
Abstract The tree-loop theorem of 't Hooft and Veltman is used in Fermi type gauges to show that gauge invariant operators in Wilson expansions mix in general with non-gauge invariant operators. Background field gauges are proposed in which this does not occur. Calculations of anomalous dimensions in these gauges are discussed.
122369912
Interacting holographic dark energy with variable deceleration parameter and accreting black holes in Bianchi type-V universe
In this paper, we have considered the spatially homogeneous and anisotropic Bianchi type-V space time filled with two interacting fluids; dark matter and a hypothetical isotropic fluid as the holographic dark energy components. To obtain an exact solution of the Einstein’s field equations, we used the assumption of time dependent deceleration parameter. We have investigated geometric and kinematic properties of the model. It is observed that the anisotropy parameter of the universe approaches to zero and the universe achieve flatness for large cosmic time. We have shown that this expanding solution is stable against the perturbation with respect to anisotropic spatial directions. We have also studied the evolution of the mass of a black hole embedded in a universe which interacts with a combination of dark matter and dark energy, considering that in the vicinity of the black hole the metric is of Schwarzschild type. We found that the black hole mass increases with the evolution of the universe, and on later epochs the increase in mass stops as dark energy accretion takes over. The results are found to be consistent with recent cosmological observations.
44195025
Subleading contributions to the black hole entropy in the brick wall approach
The brick wall model is a semiclassical approach to understand the microscopic origin of black hole entropy. In this approach, the black hole geometry is assumed to be a fixed classical background on which matter fields propagate, and the entropy of black holes supposedly arises due to the canonical entropy of matter fields outside the black hole event horizon, evaluated at the Hawking temperature. Apart from certain lower dimensional cases, the density of states of the matter fields around black holes cannot be evaluated exactly. As a result, often, in the brick wall model, the density of states and the resulting canonical entropy of the matter fields are evaluated at the leading order (in terms of ({Dirac_h}/2{pi})) in the WKB approximation. The success of the approach is reflected by the fact that the Bekenstein-Hawking area law - viz. that the entropy of black holes is equal to one-quarter the area of their event horizon, say, A{sub H} - has been recovered using this model in a variety of black hole spacetimes. In this work, we compute the canonical entropy of a quantum scalar field around static and spherically symmetric black holes through the brick wall approach at the higher ordersmore » (in fact, up to the sixth order in ({Dirac_h}/2{pi})) in the WKB approximation. We explicitly show that the brick wall model generally predicts corrections to the Bekenstein-Hawking entropy in all spacetime dimensions. In four dimensions, we find that the corrections to the Bekenstein-Hawking entropy are of the form [A{sub H}{sup n}logA{sub H}], while, in six dimensions, the corrections behave as [A{sub H}{sup m}+A{sub H}{sup n}logA{sub H}], where (m,n)<1. We compare our results with the corrections to the Bekenstein-Hawking entropy that have been obtained through the other approaches in the literature, and discuss the implications.« less
122930946
Holographic dark energy model with linearly varying deceleration parameter and generalised Chaplygin gas dark energy model in Bianchi type-I universe
The paper deals with a spatially homogeneous and anisotropic Bianchi type-I universe filled with two minimally interacting fluids; matter and holographic dark energy components. The nature of the holographic dark energy for Bianchi type-I space time is discussed. An exact solution to Einstein’s field equations in Bianchi type-I line element is obtained using the assumption of linearly varying deceleration parameter. Under the suitable condition, it is observed that the anisotropy parameter of the universe approaches to zero for large cosmic time and the coincidence parameter increases with increasing time. We established a correspondence between the holographic dark energy models with the generalised Chaplygin gas dark energy model. We also reconstructed the potential and dynamics of the scalar field which describes the Chaplygin cosmology. Solution of the field equations shows that a big rip type future singularity will occur for this model. It has been observed that the solutions are compatible with the results of recent observations.
119281634
Second Law Violations in Lovelock Gravity for Black Hole Mergers
We study the classical second law of black hole thermodynamics, for Lovelock theories (other than general relativity), in arbitrary dimensions. Using the standard formula for black hole entropy, we construct scenarios involving the merger of two black holes in which the entropy instantaneously decreases. Our construction involves a Kaluza-Klein compactification down to a dimension in which one of the Lovelock terms is topological. We discuss some open issues in the definition of the second law which might be used to remove this entropy decrease.
199678166
Horizon entropy and higher curvature equations of state
The Clausius relation between entropy change and heat flux has previously been used to derive Einstein's field equations as an equation of state. We examine here whether a similar derivation can be given for extensions beyond Einstein gravity to include higher derivative and higher curvature terms.