628 research outputs found
From Wires to Cosmology
We provide a statistical framework for characterizing stochastic particle
production in the early universe via a precise correspondence to current
conduction in wires with impurities. Our approach is particularly useful when
the microphysics is uncertain and the dynamics are complex, but only
coarse-grained information is of interest. We study scenarios with multiple
interacting fields and derive the evolution of the particle occupation numbers
from a Fokker-Planck equation. At late times, the typical occupation numbers
grow exponentially which is the analog of Anderson localization for disordered
wires. Some statistical features of the occupation numbers show hints of
universality in the limit of a large number of interactions and/or a large
number of fields. For test cases, excellent agreement is found between our
analytic results and numerical simulations.Comment: v3: minor changes and references added; matches published version in
JCA
Relativistic dark matter at the Galactic center
In a large region of the supersymmetry parameter space, the annihilation
cross section for neutralino dark matter is strongly dependent on the relative
velocity of the incoming particles. We explore the consequences of this
velocity dependence in the context of indirect detection of dark matter from
the galactic center. We find that the increase in the annihilation cross
section at high velocities leads to a flattening of the halo density profile
near the galactic center and an enhancement of the annihilation signal.Comment: 13 pages, 9 figure
Probing early-universe phase transitions with CMB spectral distortions
Global, symmetry-breaking phase transitions in the early universe can
generate scaling seed networks which lead to metric perturbations. The acoustic
waves in the photon-baryon plasma sourced by these metric perturbations, when
Silk damped, generate spectral distortions of the cosmic microwave background
(CMB). In this work, the chemical potential distortion () due to scaling
seed networks is computed and the accompanying Compton -type distortion is
estimated. The specific model of choice is the nonlinear -model
for , but the results remain the same order of magnitude for other
scaling seeds. If CMB anisotropy constraints to the model are saturated,
the resulting chemical potential distortion .Comment: 17 pages, 6 figures, v2: References added, submitted to Phys. Rev.
Gravitational perturbations from oscillons and transients after inflation
We study the scalar and tensor perturbations generated by the fragmentation
of the inflaton condensate into oscillons or transients after inflation, using
nonlinear classical lattice simulations. Without including the backreaction of
metric perturbations, we find that the magnitude of scalar metric perturbations
never exceeds a few , whereas the maximal strength of the
gravitational wave signal today is for standard
post-inflationary expansion histories. We provide parameter scalings for the
-attractor models of inflation, which can be easily applied to other
models. We also discuss the likelihood of primordial black hole formation, as
well as conditions under which the gravitational wave signal can be at
observationally interesting frequencies and amplitudes.
Finally, we provide an upper bound on the frequency of the peak of the
gravitational wave signal, which applies to all preheating scenarios.Comment: 18 pages, 8 figure
Prethermalization Production of Dark Matter
At the end of inflation, the inflaton field decays into an initially
nonthermal population of relativistic particles which eventually thermalize. We
consider the production of dark matter from this relativistic plasma, focusing
on the prethermal phase. We find that for a production cross section
with , the present dark matter abundance is produced
during the prethermal phase of its progenitors. For , entropy
production during reheating makes the nonthermal contribution to the present
dark matter abundance subdominant compared to that produced thermally. As
specific examples, we verify that the nonthermal contribution is irrelevant for
gravitino production in low scale supersymmetric models () and is dominant
for gravitino production in high scale supersymmetry models ().Comment: 12 pages, 4 figure
The charged inflaton and its gauge fields: preheating and initial conditions for reheating
We calculate particle production during inflation and in the early stages of
reheating after inflation in models with a charged scalar field coupled to
Abelian and non-Abelian gauge fields. A detailed analysis of the power spectra
of primordial electric fields, magnetic fields and charge fluctuations at the
end of inflation and preheating is provided. We carefully account for the Gauss
constraints during inflation and preheating, and clarify the role of the
longitudinal components of the electric field. We calculate the timescale for
the back-reaction of the produced gauge fields on the inflaton condensate,
marking the onset of non-linear evolution of the fields. We provide a
prescription for initial conditions for lattice simulations necessary to
capture the subsequent nonlinear dynamics. On the observational side, we find
that the primordial magnetic fields generated are too small to explain the
origin of magnetic fields on galactic scales and the charge fluctuations are
well within observational bounds for the models considered in this paper.Comment: 48 pages, 6 figures, 2 appendices, v3: references added, minor
changes to text, to appear in JCA
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