1,034 research outputs found
Cosmological Solutions of Higher-Curvature String Effective Theories with Dilatons
We study the effect of higher-curvature terms in the string low-energy
effective actions on the cosmological solutions of the theory, up to
corrections quartic in the curvatures, for the bosonic and heterotic strings as
well as the type II superstring. We find that cosmological solutions exist for
all string types but they always disappear when the dilaton field is included,
a conclusion that can be avoided if string-loop effects are taken into account.Comment: 7 pages, plain Tex with panda.tex macro (included), no figure
On a possible solution for the Polonyi problem in string cosmology
We establish the main features of homogeneous and isotropic dilaton, metric
and Yang-Mills configurations in a cosmological framework. We identify a new
energy exchange term between the dilaton and the Yang-Mills field which may
lead to a possible solution to the Polonyi problem in 4-dimensional string
models.Comment: plain Tex, 4 pages. Talk presented at the 7th Marcel Grossman
Meeting, July 1994, Stanford, USA, to appear in the proceeding
Constraints on Supergravity Chaotic Inflationary Models
We discuss, in the context of hidden sector non-minimal supergravity
chaotic inflationary models, constraints on the parameters of a polynomial
superpotential resulting from existing bounds on the reheating temperature and
on the amplitude of the primordial energy density fluctuations as inferred from
COBE. We present a specific two-parameter chaotic inflationary model which
satisfies these constraints and discuss a possible scenario for adequate baryon
asymmetry generation.Comment: Latex file, 10 pages; important changes and references adde
A Curvature Principle for the interaction between universes
We propose a Curvature Principle to describe the dynamics of interacting
universes in a multi-universe scenario and show, in the context of a simplified
model, how interaction drives the cosmological constant of one of the universes
toward a vanishingly small value. We also conjecture on how the proposed
Curvature Principle suggests a solution for the entropy paradox of a universe
where the cosmological constant vanishes.Comment: Essay selected for an honorable mention by the Gravity Research
Foundation, 2007. Plain latex, 8 page
Chaplygin inspired Inflation
We discuss chaotic inflation in the context of a phenomenological
modification of gravity inspired by the Chaplygin gas equation of state. We
find that all observationalconstraints can be satisfied provided the Chaplygin
scale is smaller than and the inflaton mass is smaller
than , respectively, where $M^2\equiv(8 \pi G)^{-1} is
the reduced Planck mass.Comment: Revtex4, 5 pages. Version to match the one published in Physics
Letters
String Theory and Cosmology
We discuss the main cosmological implications of considering string-loop
effects and a potential for the dilaton in the lowest order string effective
action. Our framework is based on the effective model arising from regarding
homogeneous and isotropic dilaton, metric and Yang-Mills field configurations.
The issues of inflation, entropy crisis and the Polonyi problem as well as the
problem of the cosmological constant are discussed.Comment: 7 pages, plain Tex, no figure
Primordial Density Fluctuations in a Dual Supergravity Cosmology
We analyse the spectrum of energy density fluctuations of a dual supergravity
model where the dilaton and the moduli are stabilized and sucessful inflation
is achieved inside domain walls that separate different vacua of the theory.
Constraints on the parameters of the superpotential are derived from the
amplitude of the primordial energy density fluctuations as inferred from COBE
and it is shown that the scale dependence of the tensor perturbations nearly
vanishes.Comment: 13 pages, Latex, 3 figures (uses epsf.sty
WMAP Constraints on the Generalized Chaplygin Gas Model
The generalized Chaplygin gas (GCG) model explains the recent accelerated
expansion of the Universe via an exotic background fluid whose equation of
state is given by p=-A/\rho^\alpha, where A is a positive constant and
0<\alpha\le 1. The model is an interesting alternative to scenarios involving
scalar field potentials, with the ensuing unnatural fine tuning conditions for
the underlying particle physics theories. We derive constraints on the
parameter space of the model from bounds on the location of the first few peaks
and troughs of the the Cosmic Microwave Background Radiation (CMBR) power
spectrum arising from recent WMAP and BOOMERanG data.Comment: 18 pages, 5 figures, version to appear in Phys. Lett.
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