28 research outputs found
Brany Liouville Inflation
We present a specific model for cosmological inflation driven by the
Liouville field in a non-critical supersymmetric string framework, in which the
departure from criticality is due to open strings stretched between the two
moving Type-II 5-branes. We use WMAP and other data on fluctuations in the
cosmic microwave background to fix parameters of the model, such as the
relative separation and velocity of the 5-branes, respecting also the
constraints imposed by data on light propagation from distant gamma-ray
bursters. The model also suggests a small, relaxing component in the present
vacuum energy that may accommodate the breaking of supersymmetry.Comment: 23 pages LATEX, two eps figures incorporated; version accepted for
publication in NJ
The Omega Effect as a Discriminant for Space-Time Foam
If there is CPT violation, the nature of entanglement for neutral meson pairs
produced in meson factories may, on general grounds, be affected. The new form
of entanglement is the omega effect. Gravitational decoherence, due to
space-time foam, may be one route for deviations from CPT invariance. Two
models of space-time foam are considered. One, based on non-critical string
theory, is able to produce the new correlations in a natural way. The other,
based on the paradigm of thermal-like baths, is shown to be surprisingly
resistant to producing the effect even on exercising a total freedom of choice
for the state of the bathComment: 10 pages, 1 figure, Invited talk at 5th International Symposium on
Quantum Theory and Symmetries, Valladolid, Spain, July 200
Quantum-Gravitational Diffusion and Stochastic Fluctuations in the Velocity of Light
We argue that quantum-gravitational fluctuations in the space-time background
give the vacuum non-trivial optical properties that include diffusion and
consequent uncertainties in the arrival times of photons, causing stochastic
fluctuations in the velocity of light ``in vacuo''. Our proposal is motivated
within a Liouville string formulation of quantum gravity that also suggests a
frequency-dependent refractive index of the particle vacuum. We construct an
explicit realization by treating photon propagation through quantum excitations
of -brane fluctuations in the space-time foam. These are described by
higher-genus string effects, that lead to stochastic fluctuations in couplings,
and hence in the velocity of light. We discuss the possibilities of
constraining or measuring photon diffusion ``in vacuo'' via -ray
observations of distant astrophysical sources.Comment: 17 pages LATEX, uses axodraw style fil
Time-Dependent Vacuum Energy Induced by D-Particle Recoil
We consider cosmology in the framework of a `material reference system' of D
particles, including the effects of quantum recoil induced by closed-string
probe particles. We find a time-dependent contribution to the cosmological
vacuum energy, which relaxes to zero as for large times . If
this energy density is dominant, the Universe expands with a scale factor . We show that this possibility is compatible with recent
observational constraints from high-redshift supernovae, and may also respect
other phenomenological bounds on time variation in the vacuum energy imposed by
early cosmology.Comment: 14 pages LATEX, no figure
Dynamical Formation of Horizons in Recoiling D Branes
A toy calculation of string/D-particle interactions within a world-sheet
approach indicates that quantum recoil effects - reflecting the gravitational
back-reaction on space-time foam due to the propagation of energetic particles
- induces the appearance of a microscopic event horizon, or `bubble', inside
which stable matter can exist. The scattering event causes this horizon to
expand, but we expect quantum effects to cause it to contract again, in a
`bounce' solution. Within such `bubbles', massless matter propagates with an
effective velocity that is less than the velocity of light in vacuo, which may
lead to observable violations of Lorentz symmetry that may be tested
experimentally. The conformal invariance conditions in the interior geometry of
the bubbles select preferentially three for the number of the spatial
dimensions, corresponding to a consistent formulation of the interaction of D3
branes with recoiling D particles, which are allowed to fluctuate independently
only on the D3-brane hypersurface.Comment: 25 pages LaTeX, 4 eps figures include
Lorentz Invariance Violation induced time delays in GRBs in different cosmological models
Lorentz Invariance Violation (LIV) manifesting itself by energy dependent
modification of standard relativistic dispersion relation has recently
attracted a considerable attention. Ellis et al. previously investigated the
energy dependent time offsets in different energy bands on a sample of gamma
ray bursts and, assuming standard cosmological model, they found a weak
indication for redshift dependence of time delays suggestive of LIV. Going
beyond the CDM cosmology we extend this analysis considering also four
alternative models of dark energy (quintessence with constant and variable
equation of state, Chaplygin gas and brane-world cosmology). It turns out that
the effect noticed by Ellis et al. is also present in those models and is the
strongest for quintessence with variable equation of state.Comment: 14 pages, 1 figur
Non-Critical Liouville String Escapes Constraints on Generic Models of Quantum Gravity
It has recently been pointed out that generic models of quantum gravity must
contend with severe phenomenological constraints imposed by gravitational
Cerenkov radiation, neutrino oscillations and the cosmic microwave background
radiation. We show how the non-critical Liouville-string model of quantum
gravity we have proposed escapes these constraints. It gives energetic
particles subluminal velocities, obviating the danger of gravitational Cerenkov
radiation. The effect on neutrino propagation is naturally flavour-independent,
obviating any impact on oscillation phenomenology. Deviations from the expected
black-body spectrum and the effects of time delays and stochastic fluctuations
in the propagation of cosmic microwave background photons are negligible, as
are their effects on observable spectral lines from high-redshift astrophysical
objects.Comment: 15 pages LaTeX, 2 eps figures include
Modified Dispersion Relations from the Renormalization Group of Gravity
We show that the running of gravitational couplings, together with a suitable
identification of the renormalization group scale can give rise to modified
dispersion relations for massive particles. This result seems to be compatible
with both the frameworks of effective field theory with Lorentz invariance
violation and deformed special relativity. The phenomenological consequences
depend on which of the frameworks is assumed. We discuss the nature and
strength of the available constraints for both cases and show that in the case
of Lorentz invariance violation, the theory would be strongly constrained.Comment: revtex4, 9 pages, updated to match published versio
As time goes by
A rather simple and non-technical exposition of our new approach to {\em
Time, Quantum Physics, Black-Hole dynamics}, and {\em Cosmology}, based on
non-critical string theory, is provided. A new fundamental principle, the {\em
Procrustean Principle}, that catches the essence of our approach is postulated:
the low-energy world is {\em unavoidably} an ``open" system due to the
spontaneous truncation of the {\em delocalized, topological} string modes in
continuous interaction with the low-lying-{\em localized} string modes. The
origin of space-time, the expansion of the Universe, the entropy increase and
accompanied irreversibility of time, as well as the collapse of the
wavefunction are all very neatly tied together. Possible observable
consequences include: quantum relaxation with time of the Universal,
fundamental constants, like the velocity of light and the Planck constant
decreasing towards their asymptotic values, and the cosmological
constant diminishing towards zero; possible violation of {\em CPT}
invariance in the system, possible apparent non-conservation of
angular momentum, and possible loss of quantum coherence in SQUID-type
experiments.Comment: CERN-TH.7260/94, 84 pages Latex (no figures
Space-Time Foam Effects on Particle Interactions and the GZK Cutoff
Modelling space-time foam using a non-critical Liouville-string model for the
quantum fluctuations of D branes with recoil, we discuss the issues of momentum
and energy conservation in particle propagation and interactions. We argue that
momentum should be conserved exactly during propagation and on the average
during interactions, but that energy is conserved only on the average during
propagation and is in general not conserved during particle interactions,
because of changes in the background metric. We discuss the possible
modification of the GZK cutoff on high-energy cosmic rays, in the light of this
energy non-conservation as well as the possible modification of the usual
relativistic momentum-energy relation.Comment: 20 pages LaTe