3,352 research outputs found
Metric perturbations at reheating: the use of spherical symmetry
We consider decay of the inflaton with a quartic potential coupled to other
fields, including gravity, but restricted to spherical symmetry. We describe
analytically an early, quasilinear regime, during which inflaton fluctuations
and the metric functions are driven by nonlinear effects of the decay products.
We present a detailed study of the leading nonlinear effects in this regime.
Results of the quasilinear approximation, in its domain of applicability, are
found to be consistent with those of fully nonlinear lattice studies. We
discuss how these results may be promoted to the full three dimensions.Comment: 18 pages, revtex, 2 figure
Resonance enhancement of particle production during reheating
We found a consistent equation of reheating after inflation, which shows that
for small quantum fluctuations the frequencies of resonance are slighted
different from the standard ones. Quantum interference is taken into account
and we found that at large fluctuations the process mimics very well the usual
parametric resonance but proceed in a different dynamical way. The analysis is
made in a toy quantum mechanical model and we discuss further its extension to
quantum field theory.Comment: 4 pages, 4 figures(eps), using RevTe
Assessment of influenza vaccine effectiveness in a sentinel surveillance network 2010–13, United States
published_or_final_versio
Improved WKB analysis of Slow-Roll Inflation
We extend the WKB method for the computation of cosmological perturbations
during inflation beyond leading order and provide the power spectra of scalar
and tensor perturbations to second order in the slow-roll parameters. Our
method does not require that the slow-roll parameters be constant. Although
leading and next-to-leading results in the slow-roll parameters depend on the
approximation technique used in the computation, we find that the inflationary
theoretical predictions obtained may reach the accuracy required by planned
observations. In two technical appendices, we compare our techniques and
results with previous findings.Comment: REVTeX 4, 13 pages, no figures, final version to appear in Phys. Rev.
On Metric Preheating
We consider the generation of super-horizon metric fluctuations during an
epoch of preheating in the presence of a scalar field \chi quadratically
coupled to the inflaton. We find that the requirement of efficient broad
resonance is concomitant with a severe damping of super-horizon \delta\chi
quantum fluctuations during inflation. Employing perturbation theory with
backreaction included as spatial averages to second order in the scalar fields
and in the metric, we argue that the usual inflationary prediction for metric
perturbations on scales relevant for structure formation is not strongly
modified.Comment: 5 latex pages, 1 postscript figure included, uses revtex.sty in two
column format and epsf.sty, some typos corrected and references added. Links
and further material at http://astro.uchicago.edu/home/web/sigl/r4.htm
Some Remarks on Oscillating Inflation
In a recent paper Damour and Mukhanov describe a scenario where inflation may
continue during the oscillatory phase. This effect is possible because the
scalar field spends a significant fraction of each period of oscillation on the
upper part of the potential. Such additional period of inflation could push
perturbations after the slow roll regime to observable scales. Although in this
work we show that the small region of the Damour-Mukhanov parameter q gives the
main contribution to oscillating inflation, it was not satisfactory understood
until now. Furthermore, it gives an expression for the energy density spectrum
of perturbations, which is well behaved in the whole physical range of q .Comment: 4 pages including figures caption, 3 ps-figures. To appear in Phys.
Rev.
Energy-Momentum Tensor of Field Fluctuations in Massive Chaotic Inflation
We study the renormalized energy-momentum tensor (EMT) of the inflaton
fluctuations in rigid space-times during the slow-rollover regime for chaotic
inflation with a mass term. We use dimensional regularization with adiabatic
subtraction and introduce a novel analytic approximation for the inflaton
fluctuations which is valid during the slow-rollover regime. Using this
approximation we find a scale invariant spectrum for the inflaton fluctuations
in a rigid space-time, and we confirm this result by numerical methods. The
resulting renormalized EMT is covariantly conserved and agrees with the
Allen-Folacci result in the de Sitter limit, when the expansion is exactly
linearly exponential in time. We analytically show that the EMT tensor of the
inflaton fluctuations grows initially in time, but saturates to the value H^2
H(0)^2, where H is the Hubble parameter and H(0) is its value when inflation
has started. This result also implies that the quantum production of light
scalar fields (with mass smaller or equal to the inflaton mass) in this model
of chaotic inflation depends on the duration of inflation and is larger than
the usual result extrapolated from the de Sitter result.Comment: revtex style, 24 pages, 6 eps figures Numerical checks added and
moduli section improve
On generation of metric perturbations during preheating
We consider the generation of the scalar mode of the metric perturbations
during preheating stage in a two field model with the potential . We discuss two possible
sources of such perturbations: a) due to the coupling between the perturbation
of the matter field and the background part of the matter field
, b) due to non-linear fluctuations in a condensate of
``particles'' of the field . Both types of the metric perturbations are
assumed to be small, and estimated using the linear theory of the metric
perturbations. We estimate analytically the upper limit of the amplitude of the
metric perturbations for all scales in the limit of so-called broad resonance,
and show that the large scale metric perturbations are very small, and taking
them into account does not influence the standard picture of the production of
the metric perturbations in inflationary scenario.Comment: This version is to be published in PRD, new references added and
typos correcte
- …