5,354 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
Systematic study of proton radioactivity of spherical proton emitters within various versions of proximity potential formalisms
In this work we present a systematic study of the proton radioactivity
half-lives of spherical proton emitters within the Coulomb and proximity
potential model. We investigate 28 different versions of the proximity
potential formalisms developed for the description of proton radioactivity,
decay and heavy particle radioactivity. It is found that 21
of them are not suitable to deal with the proton radioactivity, because the
classical turning points cannot be obtained due to the fact
that the depth of the total interaction potential between the emitted proton
and the daughter nucleus is above the proton radioactivity energy. Among the
other 7 versions of the proximity potential formalisms, it is Guo2013 which
gives the lowest rms deviation in the description of the experimental
half-lives of the known spherical proton emitters. We use this proximity
potential formalism to predict the proton radioactivity half-lives of 13
spherical proton emitters, whose proton radioactivity is energetically allowed
or observed but not yet quantified, within a factor of 3.71.Comment: 10 pages, 5 figures. This paper has been accepted by The European
Physical Journal A (in press 2019
Discuss Before Moving: Visual Language Navigation via Multi-expert Discussions
Visual language navigation (VLN) is an embodied task demanding a wide range
of skills encompassing understanding, perception, and planning. For such a
multifaceted challenge, previous VLN methods totally rely on one model's own
thinking to make predictions within one round. However, existing models, even
the most advanced large language model GPT4, still struggle with dealing with
multiple tasks by single-round self-thinking. In this work, drawing inspiration
from the expert consultation meeting, we introduce a novel zero-shot VLN
framework. Within this framework, large models possessing distinct abilities
are served as domain experts. Our proposed navigation agent, namely DiscussNav,
can actively discuss with these experts to collect essential information before
moving at every step. These discussions cover critical navigation subtasks like
instruction understanding, environment perception, and completion estimation.
Through comprehensive experiments, we demonstrate that discussions with domain
experts can effectively facilitate navigation by perceiving
instruction-relevant information, correcting inadvertent errors, and sifting
through in-consistent movement decisions. The performances on the
representative VLN task R2R show that our method surpasses the leading
zero-shot VLN model by a large margin on all metrics. Additionally, real-robot
experiments display the obvious advantages of our method over single-round
self-thinking.Comment: Submitted to ICRA 202
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