166 research outputs found
Resolving the black hole information paradox
The recent progress in string theory strongly suggests that formation and
evaporation of black holes is a unitary process. This fact makes it imperative
that we find a flaw in the semiclassical reasoning that implies a loss of
information. We propose a new criterion that limits the domain of classical
gravity: the hypersurfaces of a foliation cannot be stretched too much. This
conjectured criterion may have important consequences for the early Universe.Comment: harvmac, 11 pages (1 figure) (This essay received an ``honorable
mention'' in the Annual Essay Competition of the Gravity Research Foundation
for the year 2000.
On the Effective Equation of State of Dark Energy
In an effective field theory model with an ultraviolet momentum cutoff, there
is a relation between the effective equation of state of dark energy and the
ultraviolet cutoff scale. It implies that a measure of the equation of state of
dark energy different from minus one, does not rule out vacuum energy as dark
energy. It also indicates an interesting possibility that precise measurements
of the infrared properties of dark energy can be used to probe the ultraviolet
cutoff scale of effective quantum field theory coupled to gravity. In a toy
model with a vacuum energy dominated universe with a Planck scale cutoff, the
dark energy effective equation of state is -0.96.Comment: 7 pages, awarded honorable mention in the 2010 Gravity Research
Foundation essay competitio
AdS_3/CFT_2 correspondence at finite temperature
The AdS/CFT correspondence is established for the AdS_3 space compactified on
a solid torus with the CFT field on the boundary. Correlation functions that
correspond to the bulk theory at finite temperature are obtained in the
regularization a'la Gubser, Klebanov, and Polyakov. The BTZ black hole
solutions in AdS_3 are T-dual to the solution in the AdS_3 space without
singularity.Comment: 9pp., LaTe
Brane Decay from the Origin of Time
We present a novel scenario where matter in a spacetime originates from a
decaying brane at the origin of time. The decay could be considered as a ``Big
Bang''-like event at X^0=0. The closed string interpretation is a
time-dependent spacetime with a semi-infinite time direction, with the initial
energy of the brane converted into energy flux from the origin. The open string
interpretation can be viewed as a string theoretic non-singular initial
condition.Comment: 5 pages, 2 eps figure
A not so brief commentary on cosmological entropy bounds
There has been, quite recently, a discussion on how holographic-inspired
bounds might be used to encompass the present-day dark energy and
early-universe inflation into a single paradigm. In the current treatment, we
point out an inconsistency in the proposed framework and then provide a viable
resolution. We also elaborate on some of the implications of this framework and
further motivate the proposed holographic connection. The manuscript ends with
a more speculative note on cosmic time as an emergent (holographically induced)
construct.Comment: 12 pages and Revtex; (v2) reference added and a few cosmetic change
Dark solitons in holographic superfluids
5 pages, Revtex, 5 figures, some typos corrected. Reference addedWe construct dark soliton solutions in a holographic model of a relativistic superfluid. We study the length scales associated with the condensate and the charge density depletion, and find that the two scales differ by a non-trivial function of the chemical potential. By adjusting the chemical potential, we study the variation of the depletion of charge density at the interface.Peer reviewe
Bayesian inference of physiologically meaningful parameters from body sway measurements
The control of the human body sway by the central nervous system, muscles, and conscious brain is of interest since body sway carries information about the physiological status of a person. Several models have been proposed to describe body sway in an upright standing position, however, due to the statistical intractability of the more realistic models, no formal parameter inference has previously been conducted and the expressive power of such models for real human subjects remains unknown. Using the latest advances in Bayesian statistical inference for intractable models, we fitted a nonlinear control model to posturographic measurements, and we showed that it can accurately predict the sway characteristics of both simulated and real subjects. Our method provides a full statistical characterization of the uncertainty related to all model parameters as quantified by posterior probability density functions, which is useful for comparisons across subjects and test settings. The ability to infer intractable control models from sensor data opens new possibilities for monitoring and predicting body status in health applications.Peer reviewe
Hawking Radiation from AdS Black Holes
We investigate Hawking radiation from black holes in (d+1)-dimensional
anti-de Sitter space. We focus on s-waves, make use of the geometrical optics
approximation, and follow three approaches to analyze the radiation. First, we
compute a Bogoliubov transformation between Kruskal and asymptotic coordinates
and compare the different vacua. Second, following a method due to Kraus,
Parikh, and Wilczek, we view Hawking radiation as a tunneling process across
the horizon and compute the tunneling probablility. This approach uses an
anti-de Sitter version of a metric originally introduced by Painleve for
Schwarzschild black holes. From the tunneling probability one also finds a
leading correction to the semi-classical emission rate arising from the
backreaction to the background geometry. Finally, we consider a spherically
symmetric collapse geometry and the Bogoliubov transformation between the
initial vacuum state and the vacuum of an asymptotic observer.Comment: 13 pages, latex2e, v2: some clarifications and references adde
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