1,803 research outputs found
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
Non-Abelian (Hyperscaling Violating) Lifshitz Black Holes in General Dimensions
We consider Einstein gravities coupled to a cosmological constant and
multiple Yang-Mills fields in general dimensions and find that the
theories admit colored Lifshitz solutions with dynamic exponents . We also
introduce a Maxwell field and construct exact electric charged black holes that
asymptote to the colored Lifshitz spacetimes and analyse their
thermodynamical first law. Furthermore, we introduce a dilaton to the system
and construct Lifshitz spacetimes with hyperscaling violations. After turning
on the Maxwell field, we obtain a class of hyperscaling violating Lifshitz
black holes when .Comment: Latex, 12 pages, a published version in PL
Holographic Complexity Growth Rate in Horndeski Theory
Based on the context of complexity = action (CA) conjecture, we calculate the
holographic complexity of AdS black holes with planar and spherical topologies
in Horndeski theory. We find that the rate of change of holographic complexity
for neutral AdS black holes saturates the Lloyd's bound. For charged black
holes, we find that there exists only one horizon and thus the corresponding
holographic complexity can't be expressed as the difference of some
thermodynamical potential between two horizons as that of Reissner-Nordstrom
AdS black hole in Einstein-Maxwell theory. However, the Lloyd's bound is not
violated for charged AdS black hole in Horndeski theory.Comment: 20 pages, 6 figures, references added, typos correcte
Blandford-Znajek Process in Einsteinian Cubic Gravity
In this paper, we investigate the Blandford-Znajek (BZ) process within the
framework of Einsteinian cubic gravity (ECG). To analytically study the BZ
process using the split monopole configuration, we construct a slowly rotating
black hole in ECG up to cubic order in small spin, considering the leading
order in small coupling constant of higher curvature terms. By deriving the
magnetosphere solution around the black hole, we determine the BZ power up to
the second relative order in spin. The BZ power is modified by the coupling
constant compared to Kerr black hole. Although the general nature of the BZ
process in ECG remains unchanged at the leading order in spin, the coupling
constant introduces modification at the second relative order in spin.
Therefore, we anticipate that it is feasible to discern general relativity from
higher derivative gravities by examining the BZ power in rapidly rotating black
holes.Comment: v2: 13 pages, references adde
Godel Universe from String Theory
G\"odel universe is a direct product of a line and a three-dimensional
spacetime we call G. In this paper, we show that the G\"odel metrics
can arise as exact solutions in Einstein-Maxwell-Axion, Einstein-Proca-Axion,
or Freedman-Schwarz gauged supergravity theories. The last allows us to embed
G\"odel universe in string theory. The ten-dimensional spacetime is a direct
product of a line and the nine-dimensional one of an bundle
over G, and it can be interpreted as some decoupling limit of the
rotating D1/D5/D5 intersection. For some appropriate parameter choice, the
nine-dimensional metric becomes an AdS bundle over squashed
3-sphere. We also study the properties of the G\"odel black holes that are
constructed from the double Wick rotations of the G\"odel metrics.Comment: latex, 20 pages, discussion on null-energy condition included, typos
corrected and references adde
On the Size of Rotating Black Holes
Recently a sequence of inequalities relating the black hole horizon, photon
sphere, shadow were proposed for spherically symmetric and static black holes,
providing the upper bound for given mass. In this paper, we extend the
discussion to include rotating black holes. When viewed from the north pole
direction, the shadow remains a round disk, but the image is skewed when viewed
from the equatorial plane. After properly implementing the ``size'' parameters
for the rotating black holes, we verify that the sequence of inequalities
remain valid for a variety of solutions, including Kerr, Kerr-Newman, Kerr-Sen
and Kerr-Cveti\v c-Youm black holes. The upshot is that rotation makes both the
actual and apparent sizes of a black hole smaller.Comment: Latex, 33 page
Horndeski Gravity and the Violation of Reverse Isoperimetric Inequality
We consider Einstein-Horndeski-Maxwell gravity, together with a cosmological
constant and multiple Horndeski axions. We construct charged AdS planar black
holes in general dimensions where the Horndeski anxions span over the planar
directions. We analyse the thermodynamics and obtain the black hole volumes. We
show that the reverse isoperimetric inequality can be violated, implying that
these black holes can store information more efficiently than the Schwarzschild
black hole.Comment: Latex, 25 pages, 1 figure, references adde
Black Hole Entropy and Viscosity Bound in Horndeski Gravity
Horndeski gravities are theories of gravity coupled to a scalar field, in
which the action contains an additional non-minimal quadratic coupling of the
scalar, through its first derivative, to the Einstein tensor or the analogous
higher-derivative tensors coming from the variation of Gauss-Bonnet or Lovelock
terms. In this paper we study the thermodynamics of the static black hole
solutions in dimensions, in the simplest case of a Horndeski coupling to
the Einstein tensor. We apply the Wald formalism to calculate the entropy of
the black holes, and show that there is an additional contribution over and
above those that come from the standard Wald entropy formula. The extra
contribution can be attributed to unusual features in the behaviour of the
scalar field. We also show that a conventional regularisation to calculate the
Euclidean action leads to an expression for the entropy that disagrees with the
Wald results. This seems likely to be due to ambiguities in the subtraction
procedure. We also calculate the viscosity in the dual CFT, and show that the
viscosity/entropy ratio can violate the bound for
appropriate choices of the parameters.Comment: 30 pages, no figure, minor revision
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