121,665 research outputs found
Understanding Chinese film culture at the end of the twentieth century : the case of Not one less by Zhang Yimou
Vacua and Exact Solutions in Lower- Limits of EGB
We consider the action principles that are the lower dimensional limits of
the Einstein-Gauss-Bonnet gravity {\it via} the Kaluza-Klein route. We study
the vacua and obtain some exact solutions. We find that the reality condition
of the theories may select one vacuum over the other from the two vacua that
typically arise in Einstein-Gauss-Bonnet gravity. We obtain exact black hole
and cosmological solutions carrying scalar hair, including scalar hairy BTZ
black holes with both mass and angular momentum turned on. We also discuss the
holographic central charges in the asymptotic AdS backgrounds.Comment: Latex, 19 page
Exact Black Hole Formation in Asymptotically (A)dS and Flat Spacetimes
We consider four-dimensional Einstein gravity minimally coupled to a dilaton
scalar field with a supergravity-inspired scalar potential. We obtain an exact
time-dependent spherically symmetric solution describing gravitational collapse
to a static scalar-hairy black hole. The solution can be asymptotically AdS,
flat or dS depending on the value of the cosmological constant parameter
in the potential. As the advanced time increases, the spacetime
reaches equilibrium in an exponential fashion, i.e., with
, where is the mass of the final black
hole and is the second parameter in the potential. Similar to the
Vaidya solution, at , the spacetime can be matched to an (A)dS or flat
vacuum except that at the origin a naked singularity may occur. Moreover, a
limiting case of our solution with gives rise to an (A)dS
generalization of the Roberts solution, thereby making it relevant to critical
phenomena. Our results provide a new model for investigating formation of real
life black holes with . For , it can be instead used
to study non-equilibrium thermalization of certain strongly-coupled field
theory.Comment: Latex, 8 pages, typos corrected and references adde
Density oscillations in trapped dipolar condensates
We investigated the ground state wave function and free expansion of a
trapped dipolar condensate. We find that dipolar interaction may induce both
biconcave and dumbbell density profiles in, respectively, the pancake- and
cigar-shaped traps. On the parameter plane of the interaction strengths, the
density oscillation occurs only when the interaction parameters fall into
certain isolated areas. The relation between the positions of these areas and
the trap geometry is explored. By studying the free expansion of the condensate
with density oscillation, we show that the density oscillation is detectable
from the time-of-flight image.Comment: 7 pages, 9 figure
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