4,653 research outputs found
Viscous Asymptotically Flat Reissner-Nordstr\"om Black Branes
We study electrically charged asymptotically flat black brane solutions whose
world-volume fields are slowly varying with the coordinates. Using familiar
techniques, we compute the transport coefficients of the fluid dynamic
derivative expansion to first order. We show how the shear and bulk viscosities
are modified in the presence of electric charge and we compute the charge
diffusion constant which is not present for the neutral black p-brane. We
compute the first order dispersion relations of the effective fluid. For small
values of the charge the speed of sound is found to be imaginary and the brane
is thus Gregory-Laflamme unstable as expected. For sufficiently large values of
the charge, the sound mode becomes stable, however, in this regime the
hydrodynamic mode associated with charge diffusion is found to be unstable. The
electrically charged brane is thus found to be (classically) unstable for all
values of the charge density in agreement with general thermodynamic arguments.
Finally, we show that the shear viscosity to entropy bound is saturated, as
expected, while the proposed bounds for the bulk viscosity to entropy can be
violated in certain regimes of the charge of the brane.Comment: 28 pages, 2 figure. v3: Small changes and a few typos correcte
A new approach toward geometrical concept of black hole thermodynamics
Motivated by the energy representation of Riemannian metric, in this paper we
study different approaches toward the geometrical concept of black hole
thermodynamics. We investigate thermodynamical Ricci scalar of Weinhold,
Ruppeiner and Quevedo metrics and show that their number and location of
divergences do not coincide with phase transition points arisen from heat
capacity. Next, we introduce a new metric to solve these problems. We show that
the denominator of the Ricci scalar of the new metric contains terms which
coincide with different types of phase transitions. We elaborate the
effectiveness of the new metric and shortcomings of the previous metrics with
some examples. Furthermore, we find a characteristic behavior of the new
thermodynamical Ricci scalar which enables one to distinguish two types of
phase transitions. In addition, we generalize the new metric for the cases of
more than two extensive parameters and show that in these cases the
divergencies of thermodynamical Ricci scalar coincide with phase transition
points of the heat capacity.Comment: 13 pages with 7 figures, accepted in EPJ
Higher-Derivative Gravity with Non-minimally Coupled Maxwell Field
We construct higher-derivative gravities with a non-minimally coupled Maxwell
field. The Lagrangian consists of polynomial invariants built from the Riemann
tensor and the Maxwell field strength in such a way that the equations of
motion are second order for both the metric and the Maxwell potential. We also
generalize the construction to involve a generic non-minimally coupled -form
field strength. We then focus on one low-lying example in four dimensions and
construct the exact magnetically-charged black holes. We also construct exact
electrically-charged Lifshitz black holes. We obtain approximate dyonic
black holes for the small coupling constant or small charges. We find that the
thermodynamics based on the Wald formalism disagrees with that derived from the
Euclidean action procedure, suggesting this may be a general situation in
higher-derivative gravities with non-minimally coupled form fields. As an
application in the AdS/CFT correspondence, we study the entropy/viscosity ratio
for the AdS or Lifshitz planar black holes, and find that the exact ratio can
be obtained without having to know the details of the solutions, even for this
higher-derivative theory.Comment: Latex, 23 page
Quasinormal modes of charged magnetic black branes & chiral magnetic transport
We compute quasinormal modes (QNMs) of the metric and gauge field
perturbations about black branes electrically and magnetically charged in the
Einstein-Maxwell-Chern-Simons theory. By the gauge/gravity correspondence, this
theory is dual to a particular class of field theories with a chiral anomaly,
in a thermal charged plasma state subjected to a constant external magnetic
field, . The QNMs are dual to the poles of the two-point functions of the
energy-momentum and axial current operators, and they encode information about
the dissipation and transport of charges in the plasma. Complementary to the
gravity calculation, we work out the hydrodynamic description of the dual field
theory in the presence of a chiral anomaly, and a constant external . We
find good agreement with the weak field hydrodynamics, which can extend beyond
the weak regime into intermediate regimes. Furthermore, we provide results
that can be tested against thermodynamics and hydrodynamics in the strong
regime. We find QNMs exhibiting Landau level behavior, which become long-lived
at large if the anomaly coefficient exceeds a critical magnitude. Chiral
transport is analyzed beyond the hydrodynamic approximation for the five
(formerly) hydrodynamic modes, including a chiral magnetic wave.Comment: 29 pages + appendix, 14 figures; v2: references added, published
versio
Thermodynamics of noncommutative quantum Kerr black holes
Thermodynamic formalism for rotating black holes, characterized by
noncommutative and quantum corrections, is constructed. From a fundamental
thermodynamic relation, equations of state and thermodynamic response functions
are explicitly given and the effect of noncommutativity and quantum correction
is discussed. It is shown that the well known divergence exhibited in specific
heat is not removed by any of these corrections. However, regions of
thermodynamic stability are affected by noncommutativity, increasing the
available states for which some thermodynamic stability conditions are
satisfied.Comment: 16 pages, 9 figure
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