245 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
Leptogenesis in a Hybrid Texture Neutrino Mass Model
We investigate the CP asymmetry for a hybrid texture of the neutrino mass
matrix predicted by family symmetry in the context of the type-I seesaw
mechanism and examine its consequences for leptogenesis. We, also, calculate
the resulting Baryon Asymmetry of the Universe (BAU) for this texture.Comment: Accepted for publication in Mod. Phys. Lett.
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
Decoherence by a nonlinear environment: canonical vs. microcanonical case
We compare decoherence induced in a simple quantum system (qubit) for two
different initial states of the environment: canonical (fixed temperature) and
microcanonical (fixed energy), for the general case of a fully interacting
oscillator environment. We find that even a relatively compact oscillator bath
(with the effective number of degrees of freedom of order 10), initially in a
microcanonical state, will typically cause decoherence almost indistinguishable
from that by a macroscopic, thermal environment, except possibly at
singularities of the environment's specific heat (critical points). In the
latter case, the precise magnitude of the difference between the canonical and
microcanonical results depends on the critical behavior of the dissipative
coefficient, characterizing the interaction of the qubit with the environment.Comment: 18 pages, revtex, 2 figures; minor textual changes, corrected typo in
eq. (53) (v2); textual changes, mostly in the introduction (v3
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
Topological Defects Formation after Inflation on Lattice Simulation
We consider the formation of topological defects after inflation. In order to
take into account the effects of the rescattering of fluctuations, we integrate
the classical equation that describes the evolution of a complex scalar field
on the two-dimensional lattice with a slab symmetry. The growth of fluctuations
during preheating is found not to be enough for defect formation, and rather a
long stage of the rescattering of fluctuations after preheating is necessary.
We conclude that the topological defects are not formed if the breaking scale
\eta is lager than \sim (2 - 3)\times 10^{16} GeV.Comment: 7 pages, RevTex, 10 postscript figures included; version to be
published in Phys. Rev.
Preheating and the Einstein Field Equations
We inaugurate a framework for studying preheating and parametric resonance
after inflation without resorting to any approximations, either in
gravitational perturbation theory or in the evolution of the field(s). We do
this by numerically solving the Einstein field equations in the
post-inflationary universe. In this letter we show how to compare our results
to those of gauge invariant perturbation theory. We then verify Finelli and
Brandenberger's analysis (hep-ph/9809490) of super-horizon modes in
inflation, showing that they are not amplified by resonant effects. Lastly, we
make a preliminary survey of the nonlinear couplings between modes, which will
be important in models where the primordial metric perturbations undergo
parametric amplification.Comment: RevTeX, 5 pages, 3 figures. References added, typo in eq(16)
corrected. To appear in Phys. Rev. D (Rapid Comm.
Larger Domains from Resonant Decay of Disoriented Chiral Condensates
The decay of disoriented chiral condensates into soft pions is considered
within the context of a linear sigma model. Unlike earlier analytic studies,
which focused on the production of pions as the sigma field rolled down toward
its new equilibrium value, here we focus on the amplification of
long-wavelength pion modes due to parametric resonance as the sigma field
oscillates around the minimum of its potential. This process can create larger
domains of pion fluctuations than the usual spinodal decomposition process, and
hence may provide a viable experimental signature for chiral symmetry breaking
in relativistic heavy ion collisions; it may also better explain physically the
large growth of domains found in several numerical simulations.Comment: 4pp, 2 figs, Revtex. Minor revisions, conclusions unchange
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
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
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