413 research outputs found
On the Thermodynamics of a Gas of AdS Black Holes and the Quark-Hadron Phase Transition
We discuss the thermodynamics of a gas of black holes in five-dimensional
anti-de-Sitter (AdS) space, showing that they are described by a van der Waals
equation of state. Motivated by the Maldacena conjecture, we relate the energy
density and pressure of this non-ideal AdS black-hole gas to those of
four-dimensional gauge theory in the unconfined phase. We find that the energy
density rises rapidly above the deconfinement transition temperature, whilst
the pressure rises more slowly towards its asymptotic high-temperature value,
in qualitative agreement with lattice simulations.Comment: 15 pages, Latex, 3 figs encapsulate
Logarithmic Operators Fold D branes into AdS_3
We use logarithmic conformal field theory techniques to describe recoil
effects in the scattering of two Dirichlet branes in D dimensions. In the
particular case that a D1 brane strikes a D3 brane perpendicularly, thereby
folding it, we find that the recoil space-time is maximally symmetric, with
AdS_3 x E_{D-3} geometry. We comment on the possible applications of this
result to the study of transitions between different background metrics.Comment: 10 pages revtex, one eps figure include
A supersymmetric D-brane Model of Space-Time Foam
We present a supersymmetric model of space-time foam with two stacks of eight
D8-branes with equal string tensions, separated by a single bulk dimension
containing D0-brane particles that represent quantum fluctuations in the
space-time foam. The ground state configuration with static D-branes has zero
vacuum energy. However, gravitons and other closed-string states propagating
through the bulk may interact with the D0-particles, causing them to recoil and
the vacuum energy to become non zero. This provides a possible origin of dark
energy. Recoil also distorts the background metric felt by energetic massless
string states, which travel at less than the usual (low-energy) velocity of
light. On the other hand, the propagation of chiral matter anchored on the D8
branes is not affected by such space-time foam effects.Comment: 33 pages, latex, five figure
Light-Cone Broadening and TeV Scale Extra Dimensions
We examine the effect of light-cone broadening induced by quantum-gravity
foam in the context of theories with ``large'' extra dimensions stretching
between two parallel brane worlds. We consider the propagation of photon probes
on one of the branes, including the response to graviton fluctuations, from
both field- and string-theoretical viewpoints. In the latter approach, the
dominant source of light-cone broadening may be the recoil of the D-brane,
which scales linearly with the string coupling. Astrophysical constraints then
place strong restrictions on consistent string models of macroscopic extra
dimensions. The broadening we find in the field-theoretical picture seems to be
close to the current sensitivity of gravity-wave interferometers, and therefore
could perhaps be tested experimentally in the foreseeable future.Comment: 12 pages REVTeX, 2 axodraw figures incorporate
Time-dependent perturbations in two-dimensional String Black Holes
We discuss time-dependent perturbations (induced by matter fields) of a
black-hole background in tree-level two-dimensional string theory. We analyse
the linearized case and show the possibility of having black-hole solutions
with time-dependent horizons. The latter exist only in the presence of
time-dependent `tachyon' matter fields, which constitute the only propagating
degrees of freedom in two-dimensional string theory. For real tachyon field
configurations it is not possible to obtain solutions with horizons shrinking
to a point. On the other hand, such a possibility seems to be realized in the
case of string black-hole models formulated on higher world-sheet genera. We
connect this latter result with black hole evaporation/decay at a quantum
level.}Comment: 11 pages, two figures,UA-NPPS.9/92; CERN-TH.6671/9
Implications of Space-Time foam for Entanglement Correlations of Neutral Kaons
The role of invariance and consequences for bipartite entanglement of
neutral (K) mesons are discussed. A relaxation of leads to a modification
of the entanglement which is known as the effect. The relaxation of
assumptions required to prove the theorem are examined within the context
of models of space-time foam. It is shown that the evasion of the EPR type
entanglement implied by (which is connected with spin statistics) is
rather elusive. Relaxation of locality (through non-commutative geometry) or
the introduction of decoherence by themselves do not lead to a destruction of
the entanglement. So far we find only one model which is based on non-critical
strings and D-particle capture and recoil that leads to a stochastic
contribution to the space-time metric and consequent change in the neutral
meson bipartite entanglement. The lack of an omega effect is demonstrated for a
class of models based on thermal like baths which are generally considered as
generic models of decoherence
Derivation of a Vacuum Refractive Index in a Stringy Space-Time Foam Model
It has been suggested that energetic photons propagating in vacuo should
experience a non-trivial refractive index due to the foamy structure of
space-time induced by quantum-gravitational fluctuations. The sensitivity of
recent astrophysical observations, particularly of AGN Mk501 by the MAGIC
Collaboration, approaches the Planck scale for a refractive index depending
linearly on the photon energy. We present here a new derivation of this
quantum-gravitational vacuum refraction index, based on a stringy analogue of
the interaction of a photon with internal degrees of freedom in a conventional
medium. We model the space-time foam as a gas of D-particles in the bulk
space-time of a higher-dimensional cosmology where the observable Universe is a
D3-brane. The interaction of an open string representing a photon with a
D-particle stretches and excites the string, which subsequently decays and
re-emits the photon with a time delay that increases linearly with the photon
energy and is related to stringy uncertainty principles. We relate this
derivation to other descriptions of the quantum-gravitational refractive index
in vacuo.Comment: 8 pages, 3 eps figure
Comments on CP, T and CPT Violation in Neutral Kaon Decays
We comment on CP, T and CPT violation in the light of interesting new data
from the CPLEAR and KTeV Collaborations on neutral kaon decay asymmetries.
Other recent data from the CPLEAR experiment, constraining possible violations
of CPT and the rule, exclude the possibility that the
semileptonic-decay asymmetry measured by CPLEAR could be solely due to
CPT violation, confirming that their data constitute direct evidence for T
violation. The CP-violating asymmetry in recently
measured by the KTeV Collaboration does not by itself provide direct evidence
for T violation, but we use it to place new bounds on CPT violation.Comment: 20 pages LaTeX, Contribution to the Festschrift for L.B. Okun, to
appear in a special issue of Physics Reports, eds. V.L. Telegdi and K. Winte
On `Graceful Exit' from inflationary phase in two-dimensional Liouville String Cosmology
Within the context of a super-critical (Liouville) string, we discuss
(target-space) two-dimensional string cosmology. A numerical analysis indicates
that the identification of time with the Liouville mode results in an expanding
universe with matter which exhibits an inflationary phase, and `graceful exit'
from it, tending asymptotically to a flat-metric fixed point.This fixed point
is characterized by a dilaton configuration which, depending on the initial
conditions, either decreases linearly with the cosmic time, or is a finite
constant. This implies that, in contrast to the critical string case, the
string coupling remains bounded during the exit from the inflationary phase,
and, thus, the pertinent dynamics can be reliably described in terms of a
tree-level string effective action. The r\^ole of matter in inducing such
phenomena is emphasized. It is also interesting to note that the asymptotic
value of the vacuum energy, which in the -model framework is identified
with the `running' central charge deficit, depends crucially on the set of
initial conditions. Thus, although preliminary, this toy model seems to share
all the features expected to characterize a phenomenologically acceptable
cosmological string model.Comment: 23 pages LATEX, six eps figures incorporate
Valleys in String Foam Suppress Quantum Coherence
We exhibit string contributions to the \nd{S} matrix relating in- and out-
state density matrices that do not factorize as a product of and
matrices. They are associated with valley trajectories between
topological defects on the string world sheet, that appear as quantum
fluctuations in the space-time foam. Through their ultraviolet cut-off
dependences these valleys cause non-Hamiltonian time evolution and suppress
off-diagonal entries in the density matrix at large times.Comment: CERN-TH.6896/93, 12 pages, 1 figure, (final version to be published
in Mod. Physics Letters
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