1,156 research outputs found
Birkhoff Theorem and Matter
Birkhoff's theorem for spherically symmetric vacuum spacetimes is a key
theorem in studying local systems in general relativity theory. However
realistic local systems are only approximately spherically symmetric and only
approximately vacuum. In a previous paper, we showed the theorem remains
approximately true in an approximately spherically symmetric vacuum space time.
In this paper we prove the converse case: the theorem remains approximately
true in a spherically symmetric, approximately vacuum space time.Comment: 7 pages, Revtex
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
Possible astrophysical signatures of heavy stable neutral relics in supergravity models
We consider heavy stable neutral particles in the context of supergravity and
show that a gravitationally suppressed inflaton decay can produce such
particles in cosmologically interesting abundances within a wide mass range
. In gravity-mediated
supersymmetry breaking models, a heavy particle can decay into its superpartner
and a photon-photino pair or a gravitino. Such decays only change the identity
of a possible dark matter candidate. However, for , astrophysical bounds from gamma-ray background and
photodissociation of light elements can be more stringent than the overclosure
bound, thus ruling out the particle as a dark matter candidate.Comment: 12 page
Relaxing the Cosmological Moduli Problem
Typically the moduli fields acquire mass m =C H in the early universe, which
shifts the position of the minimum of their effective potential and leads to an
excessively large energy density of the oscillating moduli fields at the later
stages of the evolution of the universe. This constitutes the cosmological
moduli problem, or Polonyi field problem. We show that the cosmological moduli
problem can be solved or at least significantly relaxed in the theories in
which C >> 1, as well as in some models with C << 1.Comment: 9 pages, 3 Postscript figure
Structure of Fat Jets at the Tevatron and Beyond
Boosted resonances is a highly probable and enthusiastic scenario in any
process probing the electroweak scale. Such objects when decaying into jets can
easily blend with the cornucopia of jets from hard relative light QCD states.
We review jet observables and algorithms that can contribute to the
identification of highly boosted heavy jets and the possible searches that can
make use of such substructure information. We also review previous studies by
CDF on boosted jets and its measurements on specific jet shapes.Comment: invited review for a special "Top and flavour physics in the LHC era"
issue of The European Physical Journal C, we invite comments regarding
contents of the review; v2 added references and institutional preprint
number
Supergravity Inflation Free from Harmful Relics
We present a realistic supergravity inflation model which is free from the
overproduction of potentially dangerous relics in cosmology, namely moduli and
gravitinos which can lead to the inconsistencies with the predictions of baryon
asymmetry and nucleosynthesis. The radiative correction turns out to play a
crucial role in our analysis which raises the mass of supersymmetry breaking
field to intermediate scale. We pay a particular attention to the non-thermal
production of gravitinos using the non-minimal Kahler potential we obtained
from loop correction. This non-thermal gravitino production however is
diminished because of the relatively small scale of inflaton mass and small
amplitudes of hidden sector fields.Comment: 10 pages, revtex, 1 eps figure, references added, conclusion section
expande
B^F Theory and Flat Spacetimes
We propose a reduced constrained Hamiltonian formalism for the exactly
soluble theory of flat connections and closed two-forms over
manifolds with topology . The reduced phase space
variables are the holonomies of a flat connection for loops which form a basis
of the first homotopy group , and elements of the second
cohomology group of with value in the Lie algebra . When
, and if the two-form can be expressed as , for some
vierbein field , then the variables represent a flat spacetime. This is not
always possible: We show that the solutions of the theory generally represent
spacetimes with ``global torsion''. We describe the dynamical evolution of
spacetimes with and without global torsion, and classify the flat spacetimes
which admit a locally homogeneous foliation, following Thurston's
classification of geometric structures.Comment: 21 pp., Mexico Preprint ICN-UNAM-93-1
The z ~ 6 Luminosity Function Fainter than -15 mag from the Hubble Frontier Fields: The Impact of Magnification Uncertainties
Large scale structure and cosmolog
N=1 Supergravity Chaotic Inflation in the Braneworld Scenario
We study a N=1 Supergravity chaotic inflationary model, in the context of the
braneworld scenario. It is shown that successful inflation and reheating
consistent with phenomenological constraints can be achieved via the new terms
in the Friedmann equation arising from brane physics. Interestingly, the model
satisfies observational bounds with sub-Planckian field values, implying that
chaotic inflation on the brane is free from the well known difficulties
associated with the presence of higher order non-renormalizable terms in the
superpotential. A bound on the mass scale of the fifth dimension, M_5 \gsim
1.3 \times 10^{-6} M_P, is obtained from the requirement that the reheating
temperature be higher than the temperature of the electroweak phase transition.Comment: 5 pages, 1 Table, Revtex
Supersymmetry, Axions and Cosmology
Various authors have noted that in particular models, the upper bound on the
axion decay constant may not hold. We point out that within supersymmetry, this
is a generic issue. For large decay constants, the cosmological problems
associated with the axion's scalar partner are far more severe than those of
the axion. We survey a variety of models, both for the axion multiplet and for
cosmology, and find that in many cases where the cosmological problems of the
saxion are solved, the usual upper bound on the axion is significantly relaxed.
We discuss, more generally, the cosmological issues raised by the pseudoscalar
members of moduli multiplets, and find that they are potentially quite severe.Comment: 27 pages, published version, some discussions clarifie
- …