11 research outputs found
LATTICEEASY: A Program for Lattice Simulations of Scalar Fields in an Expanding Universe
We describe a C++ program that we have written and made available for calculating the evolution of interacting scalar fields in an expanding universe. The program is particularly useful for the study of reheating and thermalization after inflation. The program and its full documentation are available on the Web at http://physics.stanford.edu/gfelder/latticeeasy. In this paper we provide a brief overview of what the program does and what it is useful for
Black hole production in tachyonic preheating
We present fully non-linear simulations of a self-interacting scalar field in
the early universe undergoing tachyonic preheating. We find that density
perturbations on sub-horizon scales which are amplified by tachyonic
instability maintain long range correlations even during the succeeding
parametric resonance, in contrast to the standard models of preheating
dominated by parametric resonance. As a result the final spectrum exhibits
memory and is not universal in shape. We find that throughout the subsequent
era of parametric resonance the equation of state of the universe is almost
dust-like, hence the Jeans wavelength is much smaller than the horizon scale.
If our 2D simulations are accurate reflections of the situation in 3D, then
there are wide regions of parameter space ruled out by over-production of black
holes. It is likely however that realistic parameter values, consistent with
COBE/WMAP normalisation, are safetly outside this black hole over-production
region.Comment: 6pages, 7figures, figures correcte
Preheating with Trilinear Interactions: Tachyonic Resonance
We investigate the effects of bosonic trilinear interactions in preheating
after chaotic inflation. A trilinear interaction term allows for the complete
decay of the massive inflaton particles, which is necessary for the transition
to radiation domination. We found that typically the trilinear term is
subdominant during early stages of preheating, but it actually amplifies
parametric resonance driven by the four-legs interaction. In cases where the
trilinear term does dominate during preheating, the process occurs through
periodic tachyonic amplifications with resonance effects, which is so effective
that preheating completes within a few inflaton oscillations. We develop an
analytic theory of this process, which we call tachyonic resonance. We also
study numerically the influence of trilinear interactions on the dynamics after
preheating. The trilinear term eventually comes to dominate after preheating,
leading to faster rescattering and thermalization than could occur without it.
Finally, we investigate the role of non-renormalizable interaction terms during
preheating. We find that if they are present they generally dominate (while
still in a controllable regime) in chaotic inflation models. Preheating due to
these terms proceeds through a modified form of tachyonic resonance.Comment: 19 pages, 10 figures, refs added, published versio
Preheating in Derivatively-Coupled Inflation Models
We study preheating in theories where the inflaton couples derivatively to
scalar and gauge fields. Such couplings may dominate in natural models of
inflation, in which the flatness of the inflaton potential is related to an
approximate shift symmetry of the inflaton. We compare our results with
previously studied models with non-derivative couplings. For sufficiently heavy
scalar matter, parametric resonance is ineffective in reheating the universe,
because the couplings of the inflaton to matter are very weak. If scalar matter
fields are light, derivative couplings lead to a mild long-wavelength
instability that drives matter fields to non-zero expectation values. In this
case however, long-wavelength fluctuations of the light scalar are produced
during inflation, leading to a host of cosmological problems. In contrast,
axion-like couplings of the inflaton to a gauge field do not lead to production
of long-wavelength fluctuations during inflation. However, again because of the
weakness of the couplings to the inflaton, parametric resonance is not
effective in producing gauge field quanta.Comment: 10 pages, 9 figure
Bose Einstein condensation at reheating
We discuss the possibility that a perturbative reheating stage after
inflation produces a scalar particle gas in a Bose condensate state,
emphasizing the possible cosmological role of this phenomenon for symmetry
restoration.Comment: 4 pages, 4 figures. Revised version, with an improved analysis of the
condensate formatio
Dynamics of tachyonic preheating after hybrid inflation
We study the instability of a scalar field at the end of hybrid inflation,
using both analytical techniques and numerical simulations. We improve previous
studies by taking the inflaton field fully into account, and show that the
range of unstable modes depends sensitively on the velocity of the inflaton
field, and thereby on the Hubble rate, at the end of inflation. If topological
defects are formed, their number density is determined by the shortest unstable
wavelength. Finally, we show that the oscillations of the inflaton field
amplify the inhomogeneities in the energy density, leading to local symmetry
restoration and faster thermalization. We believe this explains why tachyonic
preheating is so effective in transferring energy away from the inflaton zero
mode.Comment: 12 pages, 10 figures, REVTeX. Minor changes, some references added.
To appear in PR
DEFROST: A New Code for Simulating Preheating after Inflation
At the end of inflation, dynamical instability can rapidly deposit the energy
of homogeneous cold inflaton into excitations of other fields. This process,
known as preheating, is rather violent, inhomogeneous and non-linear, and has
to be studied numerically. This paper presents a new code for simulating scalar
field dynamics in expanding universe written for that purpose. Compared to
available alternatives, it significantly improves both the speed and the
accuracy of calculations, and is fully instrumented for 3D visualization. We
reproduce previously published results on preheating in simple chaotic
inflation models, and further investigate non-linear dynamics of the inflaton
decay. Surprisingly, we find that the fields do not want to thermalize quite
the way one would think. Instead of directly reaching equilibrium, the
evolution appears to be stuck in a rather simple but quite inhomogeneous state.
In particular, one-point distribution function of total energy density appears
to be universal among various two-field preheating models, and is exceedingly
well described by a lognormal distribution. It is tempting to attribute this
state to scalar field turbulence.Comment: RevTeX 4.0; 16 pages, 9 figure
Turbulent Thermalization
We study, analytically and with lattice simulations, the decay of coherent
field oscillations and the subsequent thermalization of the resulting
stochastic classical wave-field. The problem of reheating of the Universe after
inflation constitutes our prime motivation and application of the results. We
identify three different stages of these processes. During the initial stage of
``parametric resonance'', only a small fraction of the initial inflaton energy
is transferred to fluctuations in the physically relevant case of sufficiently
large couplings. A major fraction is transfered in the prompt regime of driven
turbulence. The subsequent long stage of thermalization classifies as free
turbulence. During the turbulent stages, the evolution of particle distribution
functions is self-similar. We show that wave kinetic theory successfully
describes the late stages of our lattice calculation. Our analytical results
are general and give estimates of reheating time and temperature in terms of
coupling constants and initial inflaton amplitude.Comment: 27 pages, 13 figure
Reconstruction of field theory from excitation spectra of defects
We show how to reconstruct a field theory from the spectrum of bound states
on a topological defect. We apply our recipe to the case of kinks in 1+1
dimensions with one or two bound states. Our recipe successfully yields the
sine-Gordon and field theories when suitable bound state
spectra are assumed. The recipe can also be used to globally reconstruct the
inflaton potential of inflationary cosmology if the inflaton produces a
topological defect. We discuss how defects can provide ``smoking gun'' evidence
for a class of inflationary models.Comment: 10 pages, 4 figures. Included proof (Appendix B) that wall
fluctuation potentials have supersymmetric form. Added reference
Stochastic Gravitational Wave Production After Inflation
In many models of inflation, the period of accelerated expansion ends with
preheating, a highly non-thermal phase of evolution during which the inflaton
pumps energy into a specific set of momentum modes of field(s) to which it is
coupled. This necessarily induces large, transient density inhomogeneities
which can source a significant spectrum of gravitational waves. In this paper,
we consider the generic properties of gravitational waves produced during
preheating, perform detailed calculations of the spectrum for several specific
inflationary models, and identify problems that require further study. In
particular, we argue that if these gravitational waves exist they will
necessarily fall within the frequency range that is feasible for direct
detection experiments -- from laboratory through to solar system scales. We
extract the gravitational wave spectrum from numerical simulations of
preheating after and inflation, and find
that they lead to a gravitational wave amplitude of around . This is considerably higher than the amplitude of the primordial
gravitational waves produced during inflation. However, the typical wavelength
of these gravitational waves is considerably shorter than LIGO scales, although
in extreme cases they may be visible at scales accessible to the proposed BBO
mission. We survey possible experimental approaches to detecting any
gravitational wave background generated during preheating.Comment: 11 pages. Updated references. Minor clarification