18,500 research outputs found
Dyonic (A)dS Black Holes in Einstein-Born-Infeld Theory in Diverse Dimensions
We study Einstein-Born-Infeld gravity and construct the dyonic (A)dS planar
black holes in general even dimensions, that carry both the electric charge and
magnetic fluxes along the planar space. In four dimensions, the solution can be
constructed with also spherical and hyperbolic topologies. We study the black
hole thermodynamics and obtain the first law. We also classify the singularity
structure.Comment: Latex, 21 pages, typos corrected and references adde
Godel Metrics with Chronology Protection in Horndeski Gravities
G\"odel universe, one of the most interesting exact solutions predicted by
General Relativity, describes a homogeneous rotating universe containing naked
closed time-like curves (CTCs). It was shown that such CTCs are the consequence
of the null energy condition in General Relativity. In this paper, we show that
the G\"odel-type metrics with chronology protection can emerge in
Einstein-Horndeski gravity. We construct such exact solutions also in
Einstein-Horndeski-Maxwell and Einstein-Horndeski-Proca theories.Comment: Latex, 11 pages, references adde
Quantum Decoherence with Holography
Quantum decoherence is the loss of a system's purity due to its interaction
with the surrounding environment. Via the AdS/CFT correspondence, we study how
a system decoheres when its environment is a strongly-coupled theory. In the
Feynman-Vernon formalism, we compute the influence functional holographically
by relating it to the generating function of Schwinger-Keldysh propagators and
thereby obtain the dynamics of the system's density matrix.
We present two exactly solvable examples: (1) a straight string in a BTZ
black hole and (2) a scalar probe in AdS. We prepare an initial state that
mimics Schr\"odinger's cat and identify different stages of its decoherence
process using the time-scaling behaviors of R\'enyi entropy. We also relate
decoherence to local quantum quenches, and by comparing the time evolution
behaviors of the Wigner function and R\'enyi entropy we demonstrate that the
relaxation of local quantum excitations leads to the collapse of its
wave-function.Comment: 55 pages, 13 figures; v2 47 pages & 13 figs, minor revision to match
published versio
Exact Cosmological Solutions of Theories via Hojman Symmetry
Nowadays, theory has been one of the leading modified gravity theories
to explain the current accelerated expansion of the universe, without invoking
dark energy. It is of interest to find the exact cosmological solutions of
theories. Besides other methods, symmetry has been proved as a powerful
tool to find exact solutions. On the other hand, symmetry might hint the deep
physical structure of a theory, and hence considering symmetry is also well
motivated. As is well known, Noether symmetry has been extensively used in
physics. Recently, the so-called Hojman symmetry was also considered in the
literature. Hojman symmetry directly deals with the equations of motion, rather
than Lagrangian or Hamiltonian, unlike Noether symmetry. In this work, we
consider Hojman symmetry in theories in both the metric and Palatini
formalisms, and find the corresponding exact cosmological solutions of
theories via Hojman symmetry. There exist some new solutions significantly
different from the ones obtained by using Noether symmetry in theories.
To our knowledge, they also have not been found previously in the literature.
This work confirms that Hojman symmetry can bring new features to cosmology and
gravity theories.Comment: 16 pages, revtex4; v2: discussions added, Nucl. Phys. B in press; v3:
published version. arXiv admin note: text overlap with arXiv:1505.0754
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