20 research outputs found
Signals of Inflation in a Friendly String Landscape
Following Freivogel {\it et al} we consider inflation in a predictive (or
`friendly') region of the landscape of string vacua, as modeled by
Arkani-Hamed, Dimopoulos and Kachru. In such a region the dimensionful
coefficients of super-renormalizable operators unprotected by symmetries, such
as the vacuum energy and scalar mass-squareds are freely scanned over, and the
objects of study are anthropically or `environmentally' conditioned probability
distributions for observables. In this context we study the statistical
predictions of (inverted) hybrid inflation models, where the properties of the
inflaton are probabilistically distributed. We derive the resulting
distributions of observables, including the deviation from flatness
, the spectral index of scalar cosmological perturbations
(and its scale dependence ), and the ratio of tensor to scalar
perturbations . The environmental bound on the curvature implies a solution
to the -problem of inflation with the predicted distribution of
indicating values close to current observations. We find a relatively low
probability () of `just-so' inflation with measurable deviations from
flatness. Intermediate scales of inflation are preferred in these models.Comment: 20 pages, 11 figure
Equilibration times in numerical simulation of structural glasses: Comparing parallel tempering and conventional molecular dynamics
Generation of equilibrium configurations is the major obstacle for numerical
investigation of the slow dynamics in supercooled liquid states. The parallel
tempering (PT) technique, originally proposed for the numerical equilibration
of discrete spin-glass model configurations, has recently been applied in the
study of supercooled structural glasses. We present an investigation of the
ability of parallel tempering to properly sample the liquid configuration space
at different temperatures, by mapping the PT dynamics into the dynamics of the
closest local potential energy minima (inherent structures). Comparing the PT
equilibration process with the standard molecular dynamics equilibration
process we find that the PT does not increase the speed of equilibration of the
(slow) configurational degrees of freedom.Comment: 5 pages, 3 figure
An action for the exact string black hole
A local action is constructed describing the exact string black hole
discovered by Dijkgraaf, Verlinde and Verlinde in 1992. It turns out to be a
special 2D Maxwell-dilaton gravity theory, linear in curvature and field
strength. Two constants of motion exist: mass M>1, determined by the level k,
and U(1)-charge Q>0, determined by the value of the dilaton at the origin. ADM
mass, Hawking temperature T_H \propto \sqrt{1-1/M} and Bekenstein-Hawking
entropy are derived and studied in detail. Winding/momentum mode duality
implies the existence of a similar action, arising from a branch ambiguity,
which describes the exact string naked singularity. In the strong coupling
limit the solution dual to AdS_2 is found to be the 5D Schwarzschild black
hole. Some applications to black hole thermodynamics and 2D string theory are
discussed and generalizations - supersymmetric extension, coupling to matter
and critical collapse, quantization - are pointed out.Comment: 41 pages, 2 eps figures, dedicated to Wolfgang Kummer on occasion of
his Emeritierung; v2: added ref; v3: extended discussion in sections 3.2, 3.3
and at the end of 5.3 by adding 2 pages of clarifying text; updated refs;
corrected typo
Black Holes in Bulk Viscous Cosmology
We investigate the effects of the accretion of phantom energy with non-zero
bulk viscosity onto a Schwarzschild black hole and show that black holes
accreting viscous phantom energy will lose mass rapidly compared to the
non-viscous case. When matter is incorporated along with the phantom energy,
the black holes meet with the same fate as bulk viscous forces dominate matter
accretion. If the phantom energy has large bulk viscosity, then the mass of the
black hole will reduce faster than in the small viscosity case.Comment: 20 pages, 3 figures, accepted for publication in Int. J. Theor. Phy
A Kinematical Approach to Conformal Cosmology
We present an alternative cosmology based on conformal gravity, as originally
introduced by H. Weyl and recently revisited by P. Mannheim and D. Kazanas.
Unlike past similar attempts our approach is a purely kinematical application
of the conformal symmetry to the Universe, through a critical reanalysis of
fundamental astrophysical observations, such as the cosmological redshift and
others. As a result of this novel approach we obtain a closed-form expression
for the cosmic scale factor R(t) and a revised interpretation of the space-time
coordinates usually employed in cosmology. New fundamental cosmological
parameters are introduced and evaluated. This emerging new cosmology does not
seem to possess any of the controversial features of the current standard
model, such as the presence of dark matter, dark energy or of a cosmological
constant, the existence of the horizon problem or of an inflationary phase.
Comparing our results with current conformal cosmologies in the literature, we
note that our kinematic cosmology is equivalent to conformal gravity with a
cosmological constant at late (or early) cosmological times. The cosmic scale
factor and the evolution of the Universe are described in terms of several
dimensionless quantities, among which a new cosmological variable delta emerges
as a natural cosmic time. The mathematical connections between all these
quantities are described in details and a relationship is established with the
original kinematic cosmology by L. Infeld and A. Schild. The mathematical
foundations of our kinematical conformal cosmology will need to be checked
against current astrophysical experimental data, before this new model can
become a viable alternative to the standard theory.Comment: Improved version, with minor changes. 58 pages, including 7 figures
and one table. Accepted for publication in General Relativity and Gravitation
(GERG
Black Hole Thermodynamics and Statistical Mechanics
We have known for more than thirty years that black holes behave as
thermodynamic systems, radiating as black bodies with characteristic
temperatures and entropies. This behavior is not only interesting in its own
right; it could also, through a statistical mechanical description, cast light
on some of the deep problems of quantizing gravity. In these lectures, I review
what we currently know about black hole thermodynamics and statistical
mechanics, suggest a rather speculative "universal" characterization of the
underlying states, and describe some key open questions.Comment: 35 pages, Springer macros; for the Proceedings of the 4th Aegean
Summer School on Black Hole
Efficient white light generation in secondary cores of holey fibers
We report the generation of white light from a picosecond pump in the secondary cores of a holey fiber with large air-filling factor. Efficient four-wave mixing processes generate red and blue sidebands from a 530 nm green source based on a frequency-doubled Yb-doped fiber laser. Phase matching is attributed to birefringence within the sub-micrometer-sized secondary cores induced by non-symmetric deformation during the fiber drawing