156 research outputs found
Curvaton reheating: an application to braneworld inflation
The curvaton was introduced recently as a distinct inflationary mechanism for
generating adiabatic density perturbations. Implicit in that scenario is that
the curvaton offers a new mechanism for reheating after inflation, as it is a
form of energy density not diluted by the inflationary expansion. We consider
curvaton reheating in the context of a braneworld inflation model, {\em steep
inflation}, which features a novel use of the braneworld to give a new
mechanism for ending inflation. The original steep inflation model featured
reheating by gravitational particle production, but the inefficiency of that
process brings observational difficulties. We demonstrate here that the
phenomenology of steep inflation is much improved by curvaton reheating.Comment: 8 pages RevTeX4 file with two figures incorporated. Improved
referencing, matches PRD accepted versio
Curvaton reheating mechanism in inflation on warped Dvali-Gabadadze-Porrati brane
An impressed feature of inflation on warped Dvali-Gabadadze-Porrati (DGP)
brane is that the inflationary phase exits spontaneously for a scalar inflaton
field with exponential potential, which presents a graceful exit mechanism for
the inflation. But its reheating mechanism leaves open. We investigate the
curvaton reheating in inflation on warped DGP brane model. The reheating may
occur in effctively 5 dimensional or 4 dimensional stage. We study the
permitted parameter space of the curvaton field in detail. We demonstrate how
the inflation model of the warped DGP brane is improved by the curvaton
mechanism.Comment: 10 pages, 7 figures, references adde
Phase Equilibration and Magnetic Field Generation in U(1) Bubble Collisions
We present the results of lattice computations of collisions of two expanding
bubbles of true vacuum in the Abelian Higgs model with a first-order phase
transition. New time-dependent analytical solutions for the Abelian field
strength and the phase of the complex field are derived from initial conditions
inferred from linear superposition and are shown to be in excellent agreement
with the numerical solutions especially for the case where the initial phase
difference between the bubbles is small. With a step-function approximation for
the initial phase of the complex field, solutions for the Abelian field
strength and other gauge-invariant quantities are obtained in closed form.
Possible extensions of the solution to the case of the electroweak phase
transition and the generation of primordial magnetic fields are briefly
discussed.Comment: LaTeX, 41 pages, 6 figures, submitted to Physical Review
Kination Dominated Reheating and Cold Dark Matter Abundance
We consider the decay of a massive particle under the complete or partial
domination of the kinetic energy density generated by a quintessential
exponential model and we impose a number of observational constraints
originating from nucleosynthesis, the present acceleration of the universe and
the dark-energy-density parameter. We show that the presence of kination causes
a prolonged period during which the temperature is frozen to a plateau value,
much lower than the maximal temperature achieved during the process of
reheating in the absence of kination. The decoupling of a cold dark matter
particle during this period is analyzed, its relic density is calculated both
numerically and semi-analytically and the results are compared with each other.
Using plausible values (from the viewpoint of particle models) for the mass and
the thermal averaged cross section times the velocity of the cold relic, we
investigate scenaria of equilibrium or non-equilibrium production. In both
cases, acceptable results for the cold dark matter abundance can be obtained,
by constraining the initial energy density of the decaying particle, its decay
width, its mass and the averaged number of the produced cold relics. The
required plateau value of the temperature is, in most cases, lower than about
40 GeVComment: Final versio
Baryogenesis and the New Cosmology
In this talk I begin with a brief review of the status of approaches to
understanding the origin of the baryon asymmetry of the universe (BAU). I then
describe a recent model unifying three seemingly-distict problems facing
particle cosmology: the origin of inflation, the generation of the BAU and the
nature of dark energy.Comment: 16 pages, RevTeX, Plenary talk presented at PASCOS-03, Mumbai, India;
COSMO-02, Chicago, and at the Aspen Winter 2003 Conference on Particle
Physics: At the Frontiers of Particle Physics, Aspen Center for Physics. To
appear in the proceedings of PASCOS-0
Axially asymmetric fermion scattering off electroweak phase transition bubble walls with hypermagnetic fields
We show that in the presence of large scale primordial hypermagnetic fields,
it is possible to generate an axial asymmetry for a first order electroweak
phase transition. This happens during the reflection and transmission of
fermions off the true vacuum bubbles, due to the chiral nature of the fermion
coupling with the background field in the symmetric phase. We derive and solve
the Dirac equation for such fermions and compute the reflection and
transmission coefficients for the case when these fermions move from the
symmetric to the symmetry broken phase. We also comment on the possible
implications of such axial charge segregation processes for baryon number
generation.Comment: 8 pages, 2 Encapsulated Postscript figures, uses ReVTeX and
epsfig.sty, expanded discussion, version to appear in Phys. Rev.
How long before the end of inflation were observable perturbations produced?
We reconsider the issue of the number of e-foldings before the end of
inflation at which observable perturbations were generated. We determine a
plausible upper limit on that number for the standard cosmology which is around
60, with the expectation that the actual value will be up to 10 below this. We
also note a special property of the model which reduces the
uncertainties in that case and favours a higher value, giving a fairly definite
prediction of 64 e-foldings for that model. We note an extreme (and highly
implausible) situation where the number of e-foldings can be even higher,
possibly up to 100, and discuss the shortcomings of quantifying inflation by
e-foldings rather than by the change in . Finally, we discuss the impact of
non-standard evolution between the end of inflation and the present, showing
that again the expected number of e-foldings can be modified, and in some cases
significantly increased.Comment: 7 pages RevTeX4 file with one figure incorporated. Minor updates to
match version accepted by Physical Review
Structure formation with a self-tuning scalar field
A scalar field with an exponential potential has the particular property that
it is attracted into a solution in which its energy scales as the dominant
component (radiation or matter) of the Universe, contributing a fixed fraction
of the total energy density. We study the growth of perturbations in a CDM
dominated universe with this extra field, with an initial flat
spectrum of adiabatic fluctuations. The observational constraints from
structure formation are satisfied as well, or better, than in other models,
with a contribution to the energy density from the scalar field which is small enough to be consistent with entry into the attractor
prior to nucleosynthesis.Comment: 4 pages, uses RevTex, 2 figure
The shape dependence of chameleon screening
Chameleon scalar fields can screen their associated fifth forces from detection by changing their mass with the local density. These models are an archetypal example of a screening mechanism, and have become an important target for both cosmological surveys and terrestrial experiments. In particular there has been much recent interest in searching for chameleon fifth forces in the laboratory. It is known that the chameleon force is less screened around non-spherical sources, but only the field profiles around a few simple shapes are known analytically. In this work we introduce a numerical code that solves for the chameleon field around arbitrary shapes with azimuthal symmetry placed in a spherical vacuum chamber. We find that deviations from spherical symmetry can increase the chameleon acceleration experienced by a test particle, and that the least screened objects are those which minimize some internal dimension. For the shapes considered in this work, keeping the mass, density and background environment fixed, the accelerations due to the source varied by a factor of ~ 3
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