4,226 research outputs found
Gravitational waves in preheating
We study the evolution of gravitational waves through the preheating era that
follows inflation. The oscillating inflaton drives parametric resonant growth
of scalar field fluctuations, and although super-Hubble tensor modes are not
strongly amplified, they do carry an imprint of preheating. This is clearly
seen in the Weyl tensor, which provides a covariant description of
gravitational waves.Comment: 8 pages, 8 figures, Revte
A new twist to preheating
Metric perturbations typically strengthen field resonances during preheating.
In contrast we present a model in which the super-Hubble field resonances are
completely {\em suppressed} when metric perturbations are included. The model
is the nonminimal Fakir-Unruh scenario which is exactly solvable in the
long-wavelength limit when metric perturbations are included, but exhibits
exponential growth of super-Hubble modes in their absence. This gravitationally
enhanced integrability is exceptional, both for its rarity and for the power
with which it illustrates the importance of including metric perturbations in
consistent studies of preheating. We conjecture a no-go result - there exists
no {\em single-field} model with growth of cosmologically-relevant metric
perturbations during preheating.Comment: 6 pages, 3 figures, Version to appear in Physical Review
Massless Metric Preheating
Can super-Hubble metric perturbations be amplified exponentially during
preheating ? Yes. An analytical existence proof is provided by exploiting the
conformal properties of massless inflationary models. The traditional conserved
quantity \zeta is non-conserved in many regions of parameter space. We include
backreaction through the homogeneous parts of the inflaton and preheating
fields and discuss the role of initial conditions on the post-preheating
power-spectrum. Maximum field variances are strongly underestimated if metric
perturbations are ignored. We illustrate this in the case of strong
self-interaction of the decay products. Without metric perturbations,
preheating in this case is very inefficient. However, metric perturbations
increase the maximum field variances and give alternative channels for the
resonance to proceed. This implies that metric perturbations can have a large
impact on calculations of relic abundances of particles produced during
preheating.Comment: 8 pages, 4 colour figures. Version to appear in Phys. Rev. D.
Contains substantial new analysis of the ranges of parameter space for which
large changes to the inflation-produced power spectrum are expecte
Equation of state description of the dark energy transition between quintessence and phantom regimes
The dark energy crossing of the cosmological constant boundary (the
transition between the quintessence and phantom regimes) is described in terms
of the implicitly defined dark energy equation of state. The generalizations of
the models explicitly constructed to exhibit the crossing provide the insight
into the cancellation mechanism which makes the transition possible.Comment: 3 pages, talk given at TAUP200
Preheating of the nonminimally coupled inflaton field
We investigate preheating of an inflaton field coupled nonminimally to
a spacetime curvature. In the case of a self-coupling inflaton potential
, the dynamics of preheating changes by the effect of
the negative . We find that the nonminimal coupling works in two ways.
First, since the initial value of inflaton field for reheating becomes
smaller with the increase of , the evolution of the inflaton quanta is
delayed for fixed . Second, the oscillation of the inflaton field is
modified and the nonadiabatic change around occurs significantly. That
makes the resonant band of the fluctuation field wider. Especially for strong
coupling regimes , the growth of the inflaton flutuation is
dominated by the resonance due to the nonminimal coupling, which leads to the
significant enhancement of low momentum modes. Although the final variance of
the inflaton fluctuation does notchange significantly compared with the
minimally coupled case, we have found that the energy transfer from the
homogeneous inflaton to created particles efficiently occurs for .Comment: 13pages, 11figure
Reheating in the Presence of Inhomogeneous Noise
Explosive particle production due to parametric resonance is a crucial
feature of reheating in an inflationary cosmology. Coherent oscillations of the
inflaton field lead to a periodically varying mass in the evolution equation of
matter and gravitational fluctuations and often induce a parametric resonance
instability. In a previous paper (hep-ph/9709273) it was shown that homogeneous
(i.e. space independent) noise leads to an increase of the generalized Floquet
exponent for all modes, at least if the noise is temporally uncorrelated. Here
we extend the results to the physically more realistic case of spatially
inhomogeneous noise. We demonstrate - modulo some mathematical fine points
which are addressed in a companion paper - that the Floquet exponent is a non-
decreasing function of the amplitude of the noise. We provide numerical
evidence for an even stronger statement, namely that in the presence of
inhomogeneous noise, the Floquet exponent of each mode is larger than the
maximal Floquet exponent of the system in the absence of noise.Comment: 21 pages, 4 figure
Testing for double inflation with WMAP
With the WMAP data we can now begin to test realistic models of inflation
involving multiple scalar fields. These naturally lead to correlated adiabatic
and isocurvature (entropy) perturbations with a running spectral index. We
present the first full (9 parameter) likelihood analysis of double inflation
with WMAP data and find that despite the extra freedom, supersymmetric hybrid
potentials are strongly constrained with less than 7% correlated isocurvature
component allowed when standard priors are imposed on the cosomological
parameters. As a result we also find that Akaike & Bayesian model selection
criteria rather strongly prefer single-field inflation, just as equivalent
analysis prefers a cosmological constant over dynamical dark energy in the late
universe. It appears that simplicity is the best guide to our universe.Comment: 7 pages, 6 figure
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