129 research outputs found
A mass hierarchy from recoiling D branes
Using conformal field theory methods we construct a metric that describes the distortion of space-time surrounding a D(irichlet)-brane (solitonic) defect after being struck by another D-brane. By viewing our four-dimensional universe as such a struck brane, embedded in a five-dimensional space-time, we argue on the appearance of a band of massive Kaluza-Klein excitations for the bulk graviton which is localized in a region of the fifth dimension determined by the inverse size of the band. The band incorporates the massless mode (ordinary graviton) and its thickness is determined essentially by the width of the Gaussian distribution describing the (target-space) quantum fluctuations of the intersecting-brane configuration
Dynamical Flavour Symmetry Breaking by a Magnetic Field in Lattice QED_3
We perform a lattice study, in the quenched approximation, of dynamical mass
generation in a system of relativistic (Dirac) fermions, coupled to an Abelian
gauge field in (2+1)-dimensions, in the presence of an external (constant)
magnetic field, perpendicular to the spatial planes. It is shown that a strong
magnetic field catalyzes chiral symmetry breaking, in agreement with results in
the continuum. The r\^ole of the higher-Landau poles in inducing a critical
temperature above which the phenomenon disappears is pointed out. We also
discuss the implications of this model on the opening of a gap in doped
antiferromagnetic superconductors.Comment: 18 pages, latex, 9 figures, uses psfig and epsf; minor typos in
eqs.(10) and (17) correcte
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
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
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
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
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
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
D-Brane Recoil and Supersymmetry Breaking as a Relaxation Process
We propose a new mechanism for the formation of conical singularities on
D-branes by means of recoil resulting from scattering of closed string states
propagating in the (large) transverse dimensions. By viewing the (spatial part
of the) four-dimensional world as a 3-brane with large transverse dimensions
the above mechanism can lead to supersymmetry obstruction at the TeV scale. The
vacuum remains supersymmetric while the mass spectrum picks up a supersymmetry
obstructing mass splitting. The state with ``broken'' supersymmetry is not an
equilibrium ground state, but is rather an excited state of the D-brane which
relaxes to the supersymmetric ground state asymptotically in (cosmic) time.Comment: 9 pages revtex, uses axodraw style (Arguments clarified, citations
added; no change in conclusions.
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