769 research outputs found
Remarks on Cosmic String Formation during Preheating on Lattice Simulations
We reconsider the formation of (global) cosmic strings during and after
preheating by calculating the dynamics of a scalar field on both two- and
three- dimensional lattices. We have found that there is little differences
between the results in two and three dimensions about the dynamics of
fluctuations, at least, during preheating. Practically, it is difficult to
determine whether long cosmic strings which may affect the later evolution of
the universe could ever be produced from the results of simulations on
three-dimensional lattices with smaller box sizes than the horizon. Therefore,
using two-dimensional lattices with large box size, we have found that cosmic
strings with the breaking scale 0\eta \sim 10^{16} GeV are produced for broad
range of parameter space in \eta, while for higher breaking scales (\eta \sim
3\times 10^{16} GeV), their production depends crucially on the value of the
breaking scale \eta in our simulations.Comment: 7 pages, RevTex, 14 postscript figures included, to appear in Phys.
Rev.
Non-equilibrium symmetry restoration beyond one loop
We calculate the strength of symmetry restoration effects in highly
non-equilibrium states which can arise, for example, during preheating after
inflation. We show that in certain parameter range the one-loop results are
unstable, requiring summation of multiloop diagrams. We solve this problem for
the model in the large -limit and show that the symmetry restoration
may be less effective than what predicted by the one-loop estimate.Comment: Latex, 12 pages, 2 postscript figure
First-order nonthermal phase transition after preheating
During preheating after inflation, parametric resonance rapidly generates
very large fluctuations of scalar fields. In models where the inflaton field
oscillates in a double-well potential and interacts with another scalar
field , fluctuations of X can keep the \phi to -\phi symmetry temporarily
restored. If the coupling of \phi to X is much stronger than the inflaton
self-coupling, the subsequent symmetry breaking is a first-order phase
transition. We demonstrate the existence of this nonthermal phase transition
with lattice simulations of the full nonlinear dynamics of the interacting
fields. In particular, we observe nucleation of an expanding bubble.Comment: RevTeX, 4 page
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
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
Baryon number non-conservation and phase transitions at preheating
Certain inflation models undergo pre-heating, in which inflaton oscillations
can drive parametric resonance instabilities. We discuss several phenomena
stemming from such instabilities, especially in weak-scale models; generically,
these involve energizing a resonant system so that it can evade tunneling by
crossing barriers classically. One possibility is a spontaneous change of phase
from a lower-energy vacuum state to one of higher energy, as exemplified by an
asymmetric double-well potential with different masses in each well. If the
lower well is in resonance with oscillations of the potential, a system can be
driven resonantly to the upper well and stay there (except for tunneling) if
the upper well is not resonant. Another example occurs in hybrid inflation
models where the Higgs field is resonant; the Higgs oscillations can be
transferred to electroweak (EW) gauge potentials, leading to rapid transitions
over sphaleron barriers and consequent B+L violation. Given an appropriate
CP-violating seed, we find that preheating can drive a time-varying condensate
of Chern-Simons number over large spatial scales; this condensate evolves by
oscillation as well as decay into modes with shorter spatial gradients,
eventually ending up as a condensate of sphalerons. We study these examples
numerically and to some extent analytically. The emphasis in the present paper
is on the generic mechanisms, and not on specific preheating models; these will
be discussed in a later paper.Comment: 10 pages, 7 figures included, revtex, epsf, references adde
Resonant decay of Bose condensates
We present results of fully non-linear calculations of decay of the inflaton
interacting with another scalar field X. Combining numerical results for
cosmologically interesting range of resonance parameter, q \leq 10^6, with
analytical estimates, we extrapolate them to larger q. We find that scattering
of X fluctuations off the Bose condensate is a very efficient mechanism
limiting growth of X fluctuations. For a single-component X, the resulting
variance, at large q, is much smaller than that obtained in the Hartree
approximation.Comment: LaTeX, 10 pages including 4 figure
Resonant Production of Topological Defects
We describe a novel phenomenon in which vortices are produced due to resonant
oscillations of a scalar field which is driven by a periodically varying
temperature T, with T remaining much below the critical temperature .
Also, in a rapid heating of a localized region to a temperature {\it below}
, far separated vortex and antivortex can form. We compare our results
with recent models of defect production during reheating after inflation. We
also discuss possible experimental tests of our predictions of topological
defect production {\it without} ever going through a phase transition.Comment: Revtex, 13 pages including 5 postscript figure
On the new string theory inspired mechanism of generation of cosmological perturbations
Recently a non-inflationary mechanism of generation of scale-free
cosmological perturbations of metric was proposed by Brandenberger, Nayeri, and
Vafa in the context of the string gas cosmology. We discuss various problems of
their model and argue that the cosmological perturbations of metric produced in
this model have blue spectrum with a spectral index n = 5, which strongly
disagrees with observations. We conclude that this model in its present form is
not a viable alternative to inflationary cosmology.Comment: 11 pages, 1 figur
Warm tachyonic inflation in warped background
We analyze warm tachyonic inflation, proposed in the literature, but from the
viewpoint of four dimensional effective action for tachyon field on a non-BPS
D3-brane. We find that consistency with observational data on density
perturbation and validity of effective action requires warped compactification.
The number of background branes which source the flux is found to be of the
order of 10 in contrast to the order of in the standard cold
inflationary scenario.Comment: 9 pages, RevTe
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