380 research outputs found
The Ubiquitous Inflaton in String-Inspired Models
A string theory based inflationary model is developed where the inflaton
interacts with a multitude of massive string level states causing dissipation
of vacuum energy. Inflation terminates in a warm Universe without the need for
reheating.Comment: In Press Physical Review Letters 1999, modified titl
Friction in inflaton equations of motion
The possibility of a friction term in the equation of motion for a scalar
field is investigated in non-equilibrium field theory. The results obtained
differ greatly from existing estimates based on linear response theory, and
suggest that dissipation is not well represented by a term of the form
.Comment: 4 pages, 2 figures, RevTex4. An obscurity in the original version has
been clarifie
Scalar perturbation spectra from warm inflation
We present a numerical integration of the cosmological scalar perturbation
equations in warm inflation. The initial conditions are provided by a
discussion of the thermal fluctuations of an inflaton field and thermal
radiation using a combination of thermal field theory and thermodynamics. The
perturbation equations include the effects of a damping coefficient
and a thermodynamic potential . We give an analytic expression for the
spectral index of scalar fluctuations in terms of a new slow-roll parameter
constructed from . A series of toy models, inspired by spontaneous
symmetry breaking and a known form of the damping coefficient, lead to a
spectrum with on large scales and on small scales.Comment: 12 pages, 5 figures, RevTeX 4, revised with extra figure
The warm inflationary universe
In the past decade, the importance of dissipation and fluctuation to
inflationary dynamics has been realized and has led to a new picture of
inflation called warm inflation. Although these phenomena are common to
condensed matter systems, for inflation models their importance has only
recently started to be appreciated. The article describes the motivation for
these phenomenon during inflation and then examines their origins from first
principles quantum field theory treatments of inflation models. Cosmology today
is a data intensive field and this is driving theory to greater precision and
predictability. This opens the possibility to consider tests for detecting
observational signatures of dissipative processes, which will be discussed. In
addition it will be discussed how particle physics and cosmology are now
working in tandem to push the boundaries of our knowledge about fundamental
physics.Comment: 20 pages, 8 figure
Detection Limits for Super-Hubble Suppression of Causal Fluctuations
We investigate to what extent future microwave background experiments might
be able to detect a suppression of fluctuation power on large scales in flat
and open universe models. Such suppression would arise if fluctuations are
generated by causal processes, and a measurement of a small suppression scale
would be problematic for inflation models, but consistent with many defect
models. More speculatively, a measurement of a suppression scale of the order
of the present Hubble radius could provide independent evidence for a
fine-tuned inflation model leading to a low-density universe. We find that,
depending on the primordial power spectrum, a suppression scale modestly larger
than the visible Horizon can be detected, but that the detectability drops very
rapidly with increasing scale. For models with two periods of inflation, there
is essentially no possibility of detecting a causal suppression scale.Comment: 8 pages, 4 figures, revtex, In Press Physical Review D 200
Dissipation in equations of motion of scalar fields
The methods of non-equilibrium quantum field theory are used to investigate
the possibility of representing dissipation in the equation of motion for the
expectation value of a scalar field by a friction term, such as is commonly
included in phenomenological inflaton equations of motion. A sequence of
approximations is exhibited which reduces the non-equilibrium theory to a set
of local evolution equations. However, the adiabatic solution to these
evolution equations which is needed to obtain a local equation of motion for
the expectation value is not well defined; nor, therefore, is the friction
coefficient. Thus, a non-equilibrium treatment is essential, even for a system
that remains close to thermal equilibrium, and the formalism developed here
provides one means of achieving this numerically.Comment: 17 pages, 5 figure
Fine-Tuning Solution for Hybrid Inflation in Dissipative Chaotic Dynamics
We study the presence of chaotic behavior in phase space in the
pre-inflationary stage of hybrid inflation models. This is closely related to
the problem of initial conditions associated to these inflationary type of
models. We then show how an expected dissipative dynamics of fields just before
the onset of inflation can solve or ease considerably the problem of initial
conditions, driving naturally the system towards inflation. The chaotic
behavior of the corresponding dynamical system is studied by the computation of
the fractal dimension of the boundary, in phase space, separating inflationary
from non-inflationary trajectories. The fractal dimension for this boundary is
determined as a function of the dissipation coefficients appearing in the
effective equations of motion for the fields.Comment: 10 pages, 4 eps figures (uses epsf), Revtex. Replaced with version to
match one in press Physical Review
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
Taylor's (1935) dissipation surrogate reinterpreted
New results from direct numerical simulation of decaying isotropic turbulence show that Taylorâs expression for the viscous dissipation rate Δ = CΔU3/L is more appropriately interpreted as a surrogate for the inertial energy flux. As a consequence, the well known dependence of the Taylor prefactor CΔ on Reynolds number CΔ(RL)âCΔ,â can be understood as corresponding to the onset of an inertial range
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