360 research outputs found
The Relic Problem of String Gas Cosmology
We discuss the relic problem of string gas cosmology (SGC) using gravitinos
and magnetic monopoles as examples. Since SGC operates near or at the Hagedorn
temperature, relics are produced copiously; in the absence of dilution, their
abundances are too large. A subsequent phase of reheating can solve the
gravitino problem, but fails to dilute monopoles sufficiently. We propose a
subsequent phase of inflation as the most natural solution to the monopole
problem; unfortunately, inflation marginalizes almost all potential
achievements of SGC, with the exception of a possible explanation of the
dichotomy of space (why did only three dimensions inflate?).Comment: 5 pages, V2 and V3: added reference
On the Suppression of Parametric Resonance and the Viability of Tachyonic Preheating after Multi-Field Inflation
We investigate the feasibility of explosive particle production via
parametric resonance or tachyonic preheating in multi-field inflationary models
by means of lattice simulations. We observe a strong suppression of resonances
in the presence of four-leg interactions between the inflaton fields and a
scalar matter field, leading to insufficient preheating when more than two
inflatons couple to the same matter field. This suppression is caused by a
dephasing of the inflatons that increases the effective mass of the matter
field.
Including three-leg interactions leads to tachyonic preheating, which is not
suppressed by an increase in the number of fields. If four-leg interactions are
sub-dominant, we observe a slight enhancement of tachyonic preheating. Thus, in
order for preheating after multi-field inflation to be efficient, one needs to
ensure that three-leg interactions are present. If no tachyonic contributions
exist, we expect the old theory of reheating to be applicable.Comment: v2: reference added, identical with PRD version, 23 pages, 3 figure
Local random potentials of high differentiability to model the Landscape
We generate random functions locally via a novel generalization of Dyson
Brownian motion, such that the functions are in a desired differentiability
class, while ensuring that the Hessian is a member of the Gaussian orthogonal
ensemble (other ensembles might be chosen if desired). Potentials in such
higher differentiability classes are required/desirable to model string
theoretical landscapes, for instance to compute cosmological perturbations
(e.g., smooth first and second derivatives for the power-spectrum) or to search
for minima (e.g., suitable de Sitter vacua for our universe). Since potentials
are created locally, numerical studies become feasible even if the dimension of
field space is large (D ~ 100). In addition to the theoretical prescription, we
provide some numerical examples to highlight properties of such potentials;
concrete cosmological applications will be discussed in companion publications.Comment: V2: added discussion section to match published version (conclusions
unchanged); 25 pages, 5 figure
Preheating after Multi-field Inflation
In this note I study preheating after multi-field inflation to assess the
feasibility of parametric resonance. An intuitive argument for the suppression
of resonances due to dephasing of fields in generic multi-field models is
presented. This effect is absent in effective single field models, rendering
them inappropriate for the study of preheating.Comment: 4 pages, proceedings for work presented at Cargese 2008, COSMO08 and
UniverseNet second annual meetin
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