119 research outputs found
Reheating after Inflation
The theory of reheating of the Universe after inflation is developed. The
transition from inflation to the hot Universe turns out to be strongly
model-dependent and typically consists of several stages. Immediately after
inflation the field begins rapidly rolling towards the minimum of its
effective potential. Contrary to some earlier expectations, particle production
during this stage does not lead to the appearance of an extra friction term
in the equation of motion of the field . Reheating
becomes efficient only at the next stage, when the field rapidly
oscillates near the minimum of its effective potential. We have found that
typically in the beginning of this stage the classical inflaton field
very rapidly (explosively) decays into -particles or into other bosons
due to broad parametric resonance. This stage cannot be described by the
standard elementary approach to reheating based on perturbation theory. The
bosons produced at this stage, as well as some part of the classical field
which survives the stage of explosive reheating, should further decay
into other particles, which eventually become thermalized. The last stages of
decay can be described in terms of perturbation theory. Complete reheating is
possible only in those theories where a single massive -particle can
decay into other particles. This imposes strong constraints on the structure of
inflationary models. On the other hand, this means that a scalar field can be a
cold dark matter candidate even if it is strongly coupled to other fields.Comment: 7 pages, 1 figure, LaTeX, UH-IfA-94/35; SU-ITP-94-13; YITP/U-94-15
(paper replaced by its version to be published in Phys. Rev. Lett.
Suppressing the lower Multipoles in the CMB Anisotropies
The Cosmic Microwave Background (CMB) anisotropy power on the largest angular
scales observed both by WMAP and COBE DMR appears to be lower than the one
predicted by the standard model of cosmology with almost scale free primordial
perturbations arising from a period of inflation
\cite{cobe,Bennett:2003bz,Spergel,Peiris}. One can either interpret this as a
manifestation of cosmic variance or as a physical effect that requires an
explanation. We discuss various mechanisms that could be responsible for the
suppression of such low multipoles. Features in the late time evolution
of metric fluctuations may do this via the integral Sachs-Wolfe effect. Another
possibility is a suppression of power at large scales in the primordial
spectrum induced by a fast rolling stage in the evolution of the inflaton field
at the beginning of the last 65 e-folds of inflation. We illustrate this effect
in a simple model of inflation and fit the resulting CMB spectrum to the
observed temperature-temperature (TT) power spectrum. We find that the WMAP
observations suggest a cutoff at Mpc at 68% confidence, while only an upper limit of Mpc at 95%. Thus, although it improves the fit of the
data, the presence of a cutoff in power spectrum is only required at a level
close to . This is obtained with a prior which corresponds to equal
distribution wrt . We discuss how other choices (such as an equal
distribution wrt which is natural in the context of inflation) can
affect the statistical interpretation.Comment: 11 pages, 4 figures, replaced with published version, comparison with
recent papers is extende
Structure of Resonance in Preheating after Inflation
We consider preheating in the theory , where the classical oscillating inflaton field decays
into -particles and -particles. The parametric resonance which
leads to particle production in this conformally invariant theory is described
by the Lame equation. It significantly differs from the resonance in the theory
with a quadratic potential. The structure of the resonance depends in a rather
nontrivial way on the parameter . We construct the
stability/instability chart in this theory for arbitrary . We give
simple analytic solutions describing the resonance in the limiting cases
and , and in the theory with
, and with . From the point of view of parametric
resonance for , the theories with and with
have the same structure, respectively, as the theory , and
the theory of an N-component scalar field
in the limit . We show that in some of the conformally
invariant theories such as the simplest model , the
resonance can be terminated by the backreaction of produced particles long
before become of the order . We analyze the
changes in the theory of reheating in this model which appear if the inflaton
field has a small mass.Comment: 19 pages, revtex, 12 figure
Inflation and de Sitter Thermodynamics
We consider the quasi-de Sitter geometry of the inflationary universe. We
calculate the energy flux of the slowly rolling background scalar field through
the quasi-de Sitter apparent horizon and set it equal to the change of the
entropy (1/4 of the area) multiplied by the temperature, dE=TdS. Remarkably,
this thermodynamic law reproduces the Friedmann equation for the rolling scalar
field. The flux of the slowly rolling field through the horizon of the quasi-de
Sitter geometry is similar to the accretion of a rolling scalar field onto a
black hole, which we also analyze. Next we add inflaton fluctuations which
generate scalar metric perturbations. Metric perturbations result in a
variation of the area entropy. Again, the equation dE=TdS with fluctuations
reproduces the linearized Einstein equations. In this picture as long as the
Einstein equations hold, holography does not put limits on the quantum field
theory during inflation. Due to the accumulating metric perturbations, the
horizon area during inflation randomly wiggles with dispersion increasing with
time. We discuss this in connection with the stochastic decsription of
inflation. We also address the issue of the instability of inflaton
fluctuations in the ``hot tin can'' picture of de Sitter horizon.Comment: 19 pages, 5 figure
Warm inflation and scalar perturbations of the metric
A second-order expansion for the quantum fluctuations of the matter field was
considered in the framework of the warm inflation scenario. The friction and
Hubble parameters were expended by means of a semiclassical approach. The
fluctuations of the Hubble parameter generates fluctuations of the metric.
These metric fluctuations produce an effective term of curvature. The power
spectrum for the metric fluctuations can be calculated on the infrared sector.Comment: 10 pages, no figures, to be published in General Rel. and Gravitatio
Universe Reheating after Inflation
We study the problem of scalar particle production after inflation by a
rapidly oscillating inflaton field. We use the framework of the chaotic
inflation scenario with quartic and quadratic inflaton potentials. Particular
attention is paid to parametric resonance phenomena which take place in the
presence of the quickly oscillating inflaton field. We have found that in the
region of applicability of perturbation theory the effects of parametric
resonance are crucial, and estimates based on first order Born approximation
often underestimate the particle production. In the case of the quartic
inflaton potential , the particle production
process is very efficient even for small values of coupling constants. The
reheating temperature of the universe in this case is times larger than the corresponding estimates based
on first order Born approximation. In the case of the quadratic inflaton
potential the reheating process depends crucially on the type of coupling
between the inflaton and the other scalar field and on the magnitudes of the
coupling constants. If the inflaton coupling to fermions and its linear (in
inflaton field) coupling to scalar fields are suppressed, then, as previously
discussed by Kofman, Linde and Starobinsky (see e.g. Ref. 13), the inflaton
field will eventually decouple from the rest of the matter, and the residual
inflaton oscillations may provide the (cold) dark matter of the universe. In
the case of the quadratic inflaton potential we obtain the lowest and the
highest possible bounds on the effective energy density of the inflaton field
when it freezes out.Comment: 40 pages, Preprint BROWN-HET-957 (revised version, some mistakes
corrected), uses phyzz
Quantum Creation of an Open Inflationary Universe
We discuss a dramatic difference between the description of the quantum
creation of an open universe using the Hartle-Hawking wave function and the
tunneling wave function. Recently Hawking and Turok have found that the
Hartle-Hawking wave function leads to a universe with Omega = 0.01, which is
much smaller that the observed value of Omega > 0.3. Galaxies in such a
universe would be about light years away from each other, so the
universe would be practically structureless. We will argue that the
Hartle-Hawking wave function does not describe the probability of the universe
creation. If one uses the tunneling wave function for the description of
creation of the universe, then in most inflationary models the universe should
have Omega = 1, which agrees with the standard expectation that inflation makes
the universe flat. The same result can be obtained in the theory of a
self-reproducing inflationary universe, independently of the issue of initial
conditions. However, there exist two classes of models where Omega may take any
value, from Omega > 1 to Omega << 1.Comment: 23 pages, 4 figures. New materials are added. In particular, we show
that boundary terms do not help to solve the problem of unacceptably small
Omega in the new model proposed by Hawking and Turok in hep-th/9803156. A
possibility to solve the cosmological constant problem in this model using
the tunneling wave function is discusse
Ultra-High Energy Cosmic Rays, Superheavy Long-Living Particles, and Matter Creation after Inflation
The highest energy cosmic rays, above the Greisen-Zatsepin-Kuzmin cut-off of
cosmic ray spectrum, may be produced in decays of superheavy long-living
X-particles. We conjecture that these particles may be produced naturally in
the early Universe from vacuum fluctuations during inflation and may constitute
a considerable fraction of Cold Dark Matter. We predict a new cut-off in the
UHE cosmic ray spectrum E_{cut-off} < m_inflaton \approx 10^{13} GeV, the exact
position of the cut-off and the shape of the cosmic ray spectrum beyond the GZK
cut-off being determined by the QCD quark/gluon fragmentation. The Pierre Auger
Project installation might discover this phenomenon.Comment: LaTeX, 8 page
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