779 research outputs found
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
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
Criticality in Gauged Supergravities
AdS black holes show richer transition behaviors in extended phase space by
assuming the cosmological constant and its conjugate quantity to behave like
thermodynamic pressure and thermodynamic volume. We study the extended
thermodynamics of charged dilatonic AdS black holes in a class of
Einstein-Maxwell-dilaton theories that can be embedded in gauged supergravities
in various dimensions. We find that the transition behaviors of higher
dimensional dilatonic AdS black holes are different from the four dimensional
counterparts, and new transition behaviors emerges in higher dimensions. First,
there exists standard Van der Waals transition only in a five dimensional
dilatonic AdS black hole with two equal charges. Second, there emerge a new
phase transition branch in negative pressure region in six and seven
dimensional dilatonic black holes with two equal charges. Third, there emerge
transition behaviors in higher dimensional black hole with single charge cases,
which are absent in four dimensions.Comment: Latex, 18 pages, 8 figures; published versio
Exact Embeddings of JT Gravity in Strings and M-theory
We show that two-dimensional JT gravity, the holographic dual of the IR fixed
point of the SYK model, can be obtained from the consistent Kaluza-Klein
reduction of a class of EMD theories in general dimensions. For , ,
the EMD theories can be themselves embedded in supergravities. These exact
embeddings provide the holographic duals in the framework of strings and
M-theory. We find that a class of JT gravity solutions can be lifted to become
time-dependent charged extremal black holes. They can be further lifted, for
example, to describe the D1/D5-branes where the worldsheet is the Milne
universe, rather than the typical Minkowski spacetime.Comment: Latex, 25 pages, typos corrected, further discussions added, appeared
in Eur.Phys.J.
Uniqueness and structure of solutions to the Dirichlet problem for an elliptic system
AbstractIn this paper, we consider the Dirichlet problem for an elliptic system on a ball in R2. By investigating the properties for the corresponding linearized equations of solutions, and adopting the Pohozaev identity and Implicit Function Theorem, we show the uniqueness and the structure of solutions
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