1,241 research outputs found
Chaotic Inflation with Time-Variable Space Dimensions
Assuming the space dimension is not constant but decreases during the
expansion of the Universe, we study chaotic inflation with the potential
. Our investigations are based on a model Universe with variable
space dimensions. We write down field equations in the slow-roll approximation,
and define slow-roll parameters by assuming the number of space dimensions
decreases continuously as the Universe expands. The dynamical character of the
space dimension shifts the initial and final value of the inflaton field to
larger values. We obtain an upper limit for the space dimension at the Planck
length. This result is in agreement with previous works for the effective time
variation of the Newtonian gravitational constant in a model Universe with
variable space dimensions.Comment: 19 pages, To be published in Int.J.Mod.Phys.D. Minor changes to match
accepted versio
Perturbations in a non-singular bouncing Universe
We complement the low-energy gravi-dilaton effective action of string theory
with a non-local, general-covariant dilaton potential, and obtain homogeneous
solutions describing a non-singular (bouncing-curvature) cosmology. We then
compute, both analytically and numerically, the spectrum of amplified scalar
and tensor perturbations, and draw some general lessons on how to extract
observable consequences from pre-big bang and ekpyrotic scenarios.Comment: 14 pages in Latex style, 5 included figure
Generating the curvature perturbation at the end of inflation
The dominant contribution to the primordial curvature perturbation may be
generated at the end of inflation. Taking the end of inflation to be sudden,
formulas are presented for the spectrum, spectral tilt and non-gaussianity.
They are evaluated for a minimal extension of the original hybrid inflation
model.Comment: 5 pages. v3: as it will appear in JCA
Cosmological perturbations across a curvature bounce
String-inspired cosmologies, whereby a non-singular curvature bounce is
induced by a general-covariant, -duality-invariant, non-local dilaton
potential, are used to study numerically how inhomogeneities evolve and to
compare the outcome with analytic expressions obtained through different
matching conditions across the bounce. Good agreement is found if continuity
across the bounce is assumed to hold for , the curvature perturbation
on comoving hypersurfaces, rather than for the Bardeen potential.Comment: 36 pages, 5 included figure
Observational constraints on the spectral index of the cosmological curvature perturbation
We evaluate the observational constraints on the spectral index , in the
context of the CDM hypothesis which represents the simplest viable
cosmology. We first take to be practically scale-independent. Ignoring
reionization, we find at a nominal 2- level . If
we make the more realisitic assumption that reionization occurs when a fraction
to 1 of the matter has collapsed, the 2- lower bound is
unchanged while the 1- bound rises slightly. These constraints are
compared with the prediction of various inflation models. Then we investigate
the two-parameter scale-dependent spectral index, predicted by running-mass
inflation models, and find that present data allow significant scale-dependence
of , which occurs in a physically reasonable regime of parameter space.Comment: ReVTeX, 15 pages, 5 figures and 3 tables, uses epsf.sty Improved
treatment of reionization and small bug fixed in the constant n case; more
convenient parameterization and better treatment of the n dependence in the
CMB anisotropy for the running mass case; conclusions basically unchanged;
references adde
Revisiting Cosmic No-Hair Theorem for Inflationary Settings
In this work we revisit Wald's cosmic no-hair theorem in the context of
accelerating Bianchi cosmologies for a generic cosmic fluid with non-vanishing
anisotropic stress tensor and when the fluid energy momentum tensor is of the
form of a cosmological constant term plus a piece which does not respect strong
or dominant energy conditions. Such a fluid is the one appearing in
inflationary models. We show that for such a system anisotropy may grow, in
contrast to the cosmic no-hair conjecture. In particular, for a generic
inflationary model we show that there is an upper bound on the growth of
anisotropy. For slow-roll inflationary models our analysis can be refined
further and the upper bound is found to be of the order of slow-roll
parameters. We examine our general discussions and our extension of Wald's
theorem for three classes of slow-roll inflationary models, generic
multi-scalar field driven models, anisotropic models involving U(1) gauge
fields and the gauge-flation scenario.Comment: 21 pp, 4 .eps figure
Particle physics models of inflation
Inflation models are compared with observation on the assumption that the
curvature perturbation is generated from the vacuum fluctuation of the inflaton
field. The focus is on single-field models with canonical kinetic terms,
classified as small- medium- and large-field according to the variation of the
inflaton field while cosmological scales leave the horizon. Small-field models
are constructed according to the usual paradigm for beyond Standard Model
physicsComment: Based on a talk given at the 22nd IAP Colloquium, ``Inflation +25'',
Paris, June 2006 Curve omitted from final Figur
Adiabatic Modes in Cosmology
We show that the field equations for cosmological perturbations in Newtonian
gauge always have an adiabatic solution, for which a quantity is
non-zero and constant in all eras in the limit of large wavelength, so that it
can be used to connect observed cosmological fluctuations in this mode with
those at very early times. There is also a second adiabatic mode, for which
vanishes for large wavelength, and in general there may be
non-adiabatic modes as well. These conclusions apply in all eras and whatever
the constituents of the universe, under only a mild technical assumption about
the wavelength dependence of the field equations for large wave length. In the
absence of anisotropic inertia, the perturbations in the adiabatic modes are
given for large wavelength by universal formulas in terms of the
Robertson--Walker scale factor. We discuss an apparent discrepancy between
these results and what appears to be a conservation law in all modes found for
large wavelength in synchronous gauge: it turns out that, although equivalent,
synchronous and Newtonian gauges suggest inequivalent assumptions about the
behavior of the perturbations for large wavelength.Comment: 24 pages, Latex, no special macro
Affleck-Dine baryogenesis in inflating curvaton scenario with O(TeV) mass moduli curvaton
We study the Affleck-Dine (AD) baryogenesis in the inflating curvaton
scenario, when the curvaton is a moduli field with O(TeV) mass. A
moduli field with such mass is known to be free from the Polonyi problem, and
furthermore its decay products can explain the present cold dark matter
abundance. In our scenario, it further explains the primordial curvature
perturbation and the present baryon density all together. The current
observational bound on the baryon isocurvature perturbation, which severely
constrains the AD baryogenesis with the original oscillating moduli curvaton
scenario, is shown to put practically negligible constraint if we replace the
oscillating curvaton with the inflating curvaton.Comment: 1+21pages v2: minor correction v3: included short reviews, added
refs, fixed typo
Inflation from Supersymmetric Quantum Cosmology
We derive a special scalar field potential using the anisotropic Bianchi type
I cosmological model from canonical quantum cosmology under determined
conditions in the evolution to anisotropic variables . In the
process, we obtain a family of potentials that has been introduced by hand in
the literature to explain cosmological data. Considering supersymmetric quantum
cosmology, this family is scanned, fixing the exponential potential as more
viable in the inflation scenario .Comment: 14 pages, latex2e, To appear in Phys. Rev.
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