3,106 research outputs found
Exotic Statistics for Ordinary Particles in Quantum Gravity
Objects exhibiting statistics other than the familiar Bose and Fermi ones are
natural in theories with topologically nontrivial objects including geons,
strings, and black holes. It is argued here from several viewpoints that the
statistics of ordinary particles with which we are already familiar are likely
to be modified due to quantum gravity effects. In particular, such
modifications are argued to be present in loop quantum gravity and in any
theory which represents spacetime in a fundamentally piecewise-linear fashion.
The appearance of unusual statistics may be a generic feature (such as the
deformed position-momentum uncertainty relations and the appearance of a
fundamental length scale) which are to be expected in any theory of quantum
gravity, and which could be testable.Comment: Awarded an honourable mention in the 2008 Gravity Research Foundation
Essay Competitio
Large-D Expansion from Variational Perturbation Theory
We derive recursively the perturbation series for the ground-state energy of
the D-dimensional anharmonic oscillator and resum it using variational
perturbation theory (VPT). From the exponentially fast converging approximants,
we extract the coefficients of the large-D expansion to higher orders. The
calculation effort is much smaller than in the standard field-theoretic
approach based on the Hubbard-Stratonovich transformation.Comment: Author Information under http://hbar.wustl.edu/~sbrandt and
http://www.theo-phys.uni-essen.de/tp/ags/pelster_di
The Existence of Einstein Static Universes and their Stability in Fourth order Theories of Gravity
We investigate whether or not an Einstein Static universe is a solution to
the cosmological equations in gravity. It is found that only one class
of theories admits an Einstein Static model, and that this class is
neutrally stable with respect to vector and tensor perturbations for all
equations of state on all scales. Scalar perturbations are only stable on all
scales if the matter fluid equation of state satisfies
. This result is remarkably similar to
the GR case, where it was found that the Einstein Static model is stable for
.Comment: Minor changes, To appear in PR
On the origin of the difference between time and space
We suggest that the difference between time and space is due to spontaneous
symmetry breaking. In a theory with spinors the signature of the metric is
related to the signature of the Lorentz-group. We discuss a higher symmetry
that contains pseudo-orthogonal groups with arbitrary signature as subgroups.
The fundamental asymmetry between time and space arises then as a property of
the ground state rather than being put into the formulation of the theory a
priori. We show how the complex structure of quantum field theory as well as
gravitational field equations arise from spinor gravity - a fundamental spinor
theory without a metric.Comment: 4 page
Semiclassical and Quantum Black Holes and their Evaporation, de Sitter and Anti-de Sitter Regimes, Gravitational and String Phase Transitions
An effective string theory in physically relevant cosmological and black hole
space times is reviewed. Explicit computations of the quantum string entropy,
partition function and quantum string emission by black holes (Schwarzschild,
rotating, charged, asymptotically flat, de Sitter dS and AdS space times) in
the framework of effective string theory in curved backgrounds provide an
amount of new quantum gravity results as: (i) gravitational phase transitions
appear with a distinctive universal feature: a square root branch point
singularity in any space time dimensions. This is of the type of the de Vega -
Sanchez transition for the thermal self-gravitating gas of point particles.
(ii) There are no phase transitions in AdS alone. (iii) For background,
upper bounds of the Hubble constant H are found, dictated by the quantum string
phase transition.(iv) The Hawking temperature and the Hagedorn temperature are
the same concept but in different (semiclassical and quantum) gravity regimes
respectively. (v) The last stage of black hole evaporation is a microscopic
string state with a finite string critical temperature which decays as usual
quantum strings do in non-thermal pure quantum radiation (no information
loss).(vi) New lower string bounds are given for the Kerr-Newman black hole
angular momentum and charge, which are entirely different from the upper
classical bounds. (vii) Semiclassical gravity states undergo a phase transition
into quantum string states of the same system, these states are duals of each
other in the precise sense of the usual classical-quantum (wave-particle)
duality, which is universal irrespective of any symmetry or isommetry of the
space-time and of the number or the kind of space-time dimensions.Comment: review paper, no figures. to appear in Int Jour Mod Phys
Monte Carlo simulations of the screening potential of the Yukawa one-component plasma
A Monte Carlo scheme to sample the screening potential H(r) of Yukawa plasmas
notably at short distances is presented. This scheme is based on an importance
sampling technique. Comparisons with former results for the Coulombic
one-component plasma are given. Our Monte Carlo simulations yield an accurate
estimate of H(r) as well for short range and long range interparticle
distances.Comment: to be published in Journal of Physics A: Mathematical and Genera
STU Black Holes and String Triality
We find double-extreme black holes associated with the special geometry of
the Calabi-Yau moduli space with the prepotential F=STU. The area formula is
STU-moduli independent and has symmetry in space of charges.
The dual version of this theory without prepotential treats the dilaton S
asymmetric versus T,U-moduli. We display the dual relation between new (STU)
black holes and stringy (S|TU) black holes using particular Sp(8, Z)
transformation. The area formula of one theory equals that of the dual theory
when expressed in terms of dual charges. We analyse the relation between (STU)
black holes to string triality of black holes: (S|TU), (T|US), (U|ST)
solutions. In the democratic STU-symmetric version we find that all three S and
T and U duality symmetries are non-perturbative and mix electric and magnetic
charges.Comment: 12 pages, 2 Postscript figures, ref.added, minor corrections, version
to appear in Phys. Rev.
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