Related papers: Viscosity to entropy ratio at extremality
In these lectures we introduce some of the principles and techniques that are relevant for the determination of the entropy of extremal black holes by either string theory or supergravity. We consider such black holes with N=2 and N=4…
The entropy of extremal black holes (BHs) is obtained using a continuity argument from extremal quasiblack holes (QBHs). It is shown that there exists a smooth limiting transition in which (i) the system boundary approaches the extremal…
Entropy of all systems that we understand well is proportional to their volumes except for black holes given by their horizon area. This makes the microstates of any quantum theory of gravity drastically different from the ordinary matter.…
String theory is used to count microstates of four-dimensional extremal black holes in compactifications with $N=4$ and $N=8$ supersymmetry. The result agrees for large charges with the Bekenstein-Hawking entropy.
Motivated by the viscosity bound in gauge/gravity duality, we consider the ratio of shear viscosity (eta) to entropy density (s) in black hole accretion flows. We use both an ideal gas equation of state and the QCD equation of state…
The perturbation correction of general relativity has obtained the general relationship between entropy and extremality. The relation was found to exactly hold for the charged AdS black hole, and extended to the rotating and massive gravity…
Unlike the extremal Reissner - Nordstr\"{o}m black hole in ordinary spacetime, the one in anti-de Sitter spacetime is a minimum of action and has zero entropy if quantization is carried out after extremalization. However, if extremalization…
The entropy for a black hole in a de Sitter space is approached within the framework of spacetime foam. A simple model, made by $N$ wormholes in a semiclassical approximation, is taken under examination to compute the entropy for such a…
For extremal charged black holes, the thermodynamic entropy is proportional not to the area but to the mass or charges. This is demonstrated here for dyonic extremal black hole solutions of string theory. It is pointed out that these…
Motivated by the vast string landscape, we consider the shear viscosity to entropy density ratio in conformal field theories dual to Einstein gravity with curvature square corrections. After field redefinitions these theories reduce to…
Based on the generalized uncertainty principle, we study the entropy of a four-dimensional black hole by counting degrees of freedom near the horizon and obtain the (finite) entropy proportional to the surface area at the horizon without a…
We present evidence that the universal Kovtun-Son-Starinets shear viscosity to entropy density ratio of 1/4\pi can be associated with a Rindler causal horizon in flat spacetime. Since there is no known holographic (gauge/gravity) duality…
In this paper we study the ratio of shear viscosity to entropy, electrical and thermal conductivities for the R-charged black hole in STU model. We generalize previous works to the case of a black hole with three different charges. Actually…
The shear viscosity to the entropy density ratio $\eta/s$ of the anisotropic superfluid has been calculated by means of the gauge/gravity duality in the presence of the {\it dark matter} sector. The {\it dark matter} has been described by…
We calculate the ratio of shear viscosity to entropy density for a black brane of $5$-dimensional Einstein-Yang-Mills Gravity by Kubo and membrane paradigm methods. The former gives $\frac{1}{4\pi}$ exactly which is an expected result in…
We reinterpret recent work on extremal Reissner- Nordstr\o m black holes to argue that the mass is a measure of the gravitational entropy. We also find that the entropy of scalar fields in this background has a stronger divergence than…
The entropy of black holes in modified theories of gravity is examined in the Palatini formalism using the Noether Charge approach. It is shown that, if the gravitational coupling constant is properly identified, the entropy of a black hole…
Black hole entropy is studied for an exactly solvable model of two-dimensional gravity\cite{rst1}, using recently developed Noether charge techniques\cite{wald1}. This latter approach is extended to accomodate the non-local form of the…
By a simple physical consideration and uncertain principle, we derive that temperature is proportional to the surface gravity and entropy is proportional to the surface area of the black hole. We apply the same consideration to de Sitter…
We show that in theories where the lowest energy excitations are not quasiparticles but they form a continuum, the shear viscosity to entropy density ratio goes to zero as the temperature goes to zero. In these theories therefore there is…