415 research outputs found
Evolution of the Order Parameter after Bubble Collisions
If a first-order phase transition is terminated by collisions of new-phase
bubbles, there will exist a period of nonequilibrium between the time bubbles
collide and the time thermal equilibrium is established. We study the behavior
of the order parameter during this phase. We find that large nonthermal
fluctuations at this stage tend to restore symmetry, i.e., the order parameter
is smaller than its eventual thermal equilibrium value. We comment on possible
consequences for electroweak baryogenesis.Comment: 11 page LaTeX file with two figures, fig1.ps and fig2.p
A remark on sphaleron erasure of baryon asymmetry
We complete an existing result for how the baryon asymmetry left over after a
period of full thermal equilibrium depends on different lepton asymmetries.Comment: 5 pages; small clarifications and a reference added; to appear in PR
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
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
Cosmic microwave background and parametric resonance in reheating
The variation of the perturbative 3-curvature parameter, \zeta, is
investigated in the period of reheating after inflation. The two-field model
used has the inflaton, with an extra scalar field coupled to it, and non-linear
effects of both fields are included as well as a slow decay mechanism into the
hydrodynamic fluid of the radiation era. Changes in \zeta occur and persist
into the succeeding cosmic eras to influence the generation of the cosmic
microwave background fluctuations.Comment: 21 pages, 6 figures.Corrects misprinted formula and 2 number
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
Preheating in Supersymmetric Hybrid Inflation
We study preheating in a general class of supersymmetric hybrid inflation
model. Supersymmetry leads to only one coupling constant in the potential and
thus only one natural frequency of oscillation for the homogeneous fields,
whose classical evolution consequently differs from that of a general
(non-supersymmetric) hybrid model. We emphasise the importance of mixing
effects in these models which can significantly change the rate of production
of particles. We perform a general study of the rate of production of the
particles associated with the homogeneous fields, and show how preheating is
efficient in producing these quanta. Preheating of other particle species will
be model dependent, and in order to investigate this we consider a realistic
working model of supersymmetric hybrid inflation which solves the strong-CP
problem via an approximate Peccei-Quinn symmetry, which was proposed by us
previously. We study axion production in this model and show that properly
taking into account the mixing between the fields suppresses the axion
production, yet enhances the production of other particles. Finally we
demonstrate the importance of backreaction effects in this model which have the
effect of shutting off axion production, leaving the axion safely within
experimental bounds.Comment: 37 pages, Latex, 11 eps figures, 14 ps (colour) figure
Patterns from preheating
The formation of regular patterns is a well-known phenomenon in condensed
matter physics. Systems that exhibit pattern formation are typically driven and
dissipative with pattern formation occurring in the weakly non-linear regime
and sometimes even in more strongly non-linear regions of parameter space. In
the early universe, parametric resonance can drive explosive particle
production called preheating. The fields that are populated then decay quantum
mechanically if their particles are unstable. Thus, during preheating, a
driven-dissipative system exists. In this paper, we show that a self-coupled
inflaton oscillating in its potential at the end of inflation can exhibit
pattern formation.Comment: 4 pages, RevTex, 6 figure
Particle production in the oscillating inflation model
We investigate the particle production of a scalar field coupled to an
inflaton field () in the {\it oscillating inflation}
model, which was recently proposed by Damour and Mukhanov. Although the
fluctuation of the field can be effectively enhanced during a stage of
the oscillating inflation, the maximum fluctuation is suppressed as the
critical value which indicates the scale of the core part of the
inflaton potential decreases, in taking into account the back reaction effect
of created particles. As for the particle production, we find that
larger values of the coupling constant are required to lead to an efficient
parametric resonance with the decrease of , because an effective mass
of inflaton around the minimum of its potential becomes larger. However, it is
possible to generate the superheavy particle whose mass is greater than
GeV, which would result in an important consequence for the GUT
baryogenesis.Comment: 18 pages, 14 figure
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