459 research outputs found

### Contribution of the hybrid inflation waterfall to the primordial curvature perturbation

A contribution $\zeta_\chi$ to the curvature perturbation will be generated
during the waterfall that ends hybrid inflation, that may be significant on
small scales. In particular, it may lead to excessive black hole formation. We
here consider standard hybrid inflation, where the tachyonic mass of the
waterfall field is much bigger than the Hubble parameter. We calculate
$\zeta_\chi$ in the simplest case, and see why earlier calculations of
$\zeta_\chi$ are incorrect.Comment: Simpler and more complete results, especiallly for delta N approac

### Affleck-Dine baryogenesis in inflating curvaton scenario with O($10-10^2$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($10-10^2$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

### Large-scale Perturbations from the Waterfall Field in Hybrid Inflation

We estimate large-scale curvature perturbations from isocurvature
fluctuations in the waterfall field during hybrid inflation, in addition to the
usual inflaton field perturbations. The tachyonic instability at the end of
inflation leads to an explosive growth of super-Hubble scale perturbations, but
they retain the steep blue spectrum characteristic of vacuum fluctuations in a
massive field during inflation. The power spectrum thus peaks around the
Hubble-horizon scale at the end of inflation. We extend the usual delta-N
formalism to include the essential role of these small fluctuations when
estimating the large-scale curvature perturbation. The resulting curvature
perturbation due to fluctuations in the waterfall field is second-order and the
spectrum is expected to be of order 10^{-54} on cosmological scales.Comment: 10 pages, 4 figures; v2 comments added on application of delta-N
formalism including Hubble scale fluctuation

### Curvaton and the inhomogeneous end of inflation

We study the primordial density perturbations and non-Gaussianities generated
from the combined effects of an inhomogeneous end of inflation and curvaton
decay in hybrid inflation. This dual role is played by a single isocurvature
field which is massless during inflation but acquire a mass at the end of
inflation via the waterfall phase transition. We calculate the resulting
primordial non-Gaussianity characterized by the non-linearity parameter,
$f_{NL}$, recovering the usual end-of-inflation result when the field decays
promptly and the usual curvaton result if the field decays sufficiently late.Comment: 13 pages, 5 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

### Running-Mass Inflation Model and Primordial Black Holes

We revisit the question whether the running-mass inflation model allows the
formation of Primordial Black Holes (PBHs) that are sufficiently long-lived to
serve as candidates for Dark Matter. We incorporate recent cosmological data,
including the WMAP 7-year results. Moreover, we include "the running of the
running" of the spectral index of the power spectrum, as well as the
renormalization group "running of the running" of the inflaton mass term. Our
analysis indicates that formation of sufficiently heavy, and hence long-lived,
PBHs still remains possible in this scenario. As a by-product, we show that the
additional term in the inflaton potential still does not allow significant
negative running of the spectral index.Comment: 22 pages, 6 figures, Refs. added, Published in JCA

### Evolution of fNL to the adiabatic limit

We study inflationary perturbations in multiple-field models, for which zeta
typically evolves until all isocurvature modes decay--the "adiabatic limit". We
use numerical methods to explore the sensitivity of the nonlinear parameter fNL
to the process by which this limit is achieved, finding an appreciable
dependence on model-specific data such as the time at which slow-roll breaks
down or the timescale of reheating. In models with a sum-separable potential
where the isocurvature modes decay before the end of the slow-roll phase we
give an analytic criterion for the asymptotic value of fNL to be large. Other
examples can be constructed using a waterfall field to terminate inflation
while fNL is transiently large, caused by descent from a ridge or convergence
into a valley. We show that these two types of evolution are distinguished by
the sign of the bispectrum, and give approximate expressions for the peak fNL.Comment: v1: 25 pages, plus Appendix and bibliography, 6 figures. v2: minor
edits to match published version in JCA

### Hilltop Non-Gaussianity

We study non-Gaussianity induced by a pseudo Nambu-Goldstone boson with a
cosine-type scalar potential. We focus on how the non-Gaussianity is affected
when the pseudo Nambu-Goldstone boson rolls down from near the top of the
scalar potential where the deviation from a quadratic potential is large. We
find that the resultant non-Gaussianity is similar to that obtained in the
quadratic potential, if the pseudo Nambu-Goldstone boson accounts for the
curvature perturbation; the non-Gaussianity is enhanced, otherwise.Comment: 12 pages, 3 figures; References added; to appear in JCA

### Multiple field inflation

Inflation offers a simple model for very early evolution of our Universe and
the origin of primordial perturbations on large scales. Over the last 25 years
we have become familiar with the predictions of single-field models, but
inflation with more than one light scalar field can alter preconceptions about
the inflationary dynamics and our predictions for the primordial perturbations.
I will discuss how future observational data could distinguish between
inflation driven by one field, or many fields. As an example, I briefly review
the curvaton as an alternative to the inflaton scenario for the origin of
structure.Comment: 27 pages, no figures. To appear in proceedings of 22nd IAP
Colloquium, Inflation +25, Paris, June 200

### On the Generation of a Scale-Invariant Spectrum of Adiabatic Fluctuations in Cosmological Models with a Contracting Phase

In Pre-Big-Bang and in Ekpyrotic Cosmology, perturbations on cosmological
scales today are generated from quantum vacuum fluctuations during a phase when
the Universe is contracting (viewed in the Einstein frame). The backgrounds
studied to date do not yield a scale invariant spectrum of adiabatic
fluctuations. Here, we present a new contracting background model (neither of
Pre-Big-Bang nor of the Ekpyrotic form) involving a single scalar field coupled
to gravity in which a scale-invariant spectrum of curvature fluctuations and
gravitational waves results. The equation of state of this scalar field
corresponds to cold matter. We demonstrate that if this contracting phase can
be matched via a nonsingular bounce to an expanding Friedmann cosmology, the
scale-invariance of the curvature fluctuations is maintained. We also find new
background solutions for Pre-Big-Bang and for Ekpyrotic cosmology, which
involve two scalar fields with exponential potentials with background values
which are evolving in time. We comment on the difficulty of obtaining a
scale-invariant spectrum of adiabatic fluctuations with background solutions
which have been studied in the past.Comment: 8 pages, revised version without the section on perturbations,
matching the version published on Phys. Rev. D. For cosmological
perturbations in the two field model see astro-ph/021127

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