94 research outputs found
Inhomogeneous Neutrino Degeneracy and Big Bang Nucleosynthesis
We examine Big Bang nucleosynthesis (BBN) in the case of inhomogenous
neutrino degeneracy, in the limit where the fluctuations are sufficiently small
on large length scales that the present-day element abundances are homogeneous.
We consider two representive cases: degeneracy of the electron neutrino alone,
and equal chemical potentials for all three neutrinos. We use a linear
programming method to constrain an arbitrary distribution of the chemical
potentials. For the current set of (highly-restrictive) limits on the
primordial element abundances, homogeneous neutrino degeneracy barely changes
the allowed range of the baryon-to-photon ratio. Inhomogeneous degeneracy
allows for little change in the lower bound on the baryon-to-photon ratio, but
the upper bound in this case can be as large as 1.1 \times 10^{-8} (only
electron neutrino degeneracy) or 1.0 \times 10^{-9} (equal degeneracies for all
three neutrinos). For the case of inhomogeneous neutrino degeneracy, we show
that there is no BBN upper bound on the neutrino energy density, which is
bounded in this case only by limits from structure formation and the cosmic
microwave background.Comment: 6 pages, no figure
Monte Carlo reconstruction of the inflationary potential
We present Monte Carlo reconstruction, a new method for ``inverting''
observational data to constrain the form of the scalar field potential
responsible for inflation. This stochastic technique is based on the flow
equation formalism and has distinct advantages over reconstruction methods
based on a Taylor expansion of the potential. The primary ansatz required for
Monte Carlo reconstruction is simply that inflation is driven by a single
scalar field. We also require a very mild slow roll constraint, which can be
made arbitrarily weak since Monte Carlo reconstruction is implemented at
arbitrary order in the slow roll expansion. While our method cannot evade
fundamental limits on the accuracy of reconstruction, it can be simply and
consistently applied to poor data sets, and it takes advantage of the attractor
properties of single-field inflation models to constrain the potential outside
the small region directly probed by observations. We show examples of Monte
Carlo reconstruction for data sets similar to that expected from the Planck
satellite, and for a hypothetical measurement with a factor of five better
parameter discrimination than Planck.Comment: 10 pages, 5 figures (RevTeX 4) Version submitted to PRD: references
added, minor clarification
Inflation: flow, fixed points and observables to arbitrary order in slow roll
I generalize the inflationary flow equations of Hoffman and Turner to
arbitrary order in slow roll. This makes it possible to study the predictions
of slow roll inflation in the full observable parameter space of tensor/scalar
ratio , spectral index , and running . It also becomes
possible to identify exact fixed points in the parameter flow. I numerically
evaluate the flow equations to fifth order in slow roll for a set of randomly
chosen initial conditions and find that the models cluster strongly in the
observable parameter space, indicating a ``generic'' set of predictions for
slow roll inflation. I comment briefly on the the interesting proposed
correspondence between flow in inflationary parameter space and renormalization
group flow in a boundary conformal field theory.Comment: 16 pages, 7 figures. LaTeX. V4: Fixed important error in numerical
constant in the second-order slow roll expressions for the observables r, n,
and dn/dlog(k). See footnote after Eq. (48). New figures, minor changes to
conclusions. Supersedes version published in Phys. Rev.
Non-canonical generalizations of slow-roll inflation models
We consider non-canonical generalizations of two classes of simple
single-field inflation models. First, we study the non-canonical version of
"ultra-slow roll" inflation, which is a class of inflation models for which
quantum modes do not freeze at horizon crossing, but instead evolve rapidly on
superhorizon scales. Second, we consider the non-canonical generalization of
the simplest "chaotic" inflation scenario, with a potential dominated by a
quartic (mass) term for the inflaton. We find a class of related non-canonical
solutions with polynomial potentials, but with varying speed of sound. These
solutions are characterized by a constant field velocity, and we dub such
models {\it isokinetic} inflation. As in the canonical limit, isokinetic
inflation has a slightly red-tilted power spectrum, consistent with current
data. Unlike the canonical case, however, these models can have an arbitrarily
small tensor/scalar ratio. Of particular interest is that isokinetic inflation
is marked by a correlation between the tensor/scalar ratio and the amplitude of
non-Gaussianity such that parameter regimes with small tensor/scalar ratio have
{\it large} associated non-Gaussianity, which is a distinct observational
signature.Comment: 12 pages, 3 figures, LaTeX; V2: version submitted to JCAP. References
adde
On the inflationary flow equations
I explore properties of the inflationary flow equations. I show that the flow
equations do not correspond directly to inflationary dynamics. Nevertheless,
they can be used as a rather complicated algorithm for generating inflationary
models. I demonstrate that the flow equations can be solved analytically and
give a closed form solution for the potentials to which flow equation solutions
correspond. I end by considering some simpler algorithms for generating
stochastic sets of slow-roll inflationary models for confrontation with
observational data.Comment: 4 pages RevTeX4 file. Corrected typos in Eqs 11 and 13. Supersedes
journal versio
A generic estimate of trans-Planckian modifications to the primordial power spectrum in inflation
We derive a general expression for the power spectra of scalar and tensor
fluctuations generated during inflation given an arbitrary choice of boundary
condition for the mode function at a short distance. We assume that the
boundary condition is specified at a short-distance cutoff at a scale which
is independent of time. Using a particular prescription for the boundary
condition at momentum , we find that the modulation to the power spectra
of density and gravitational wave fluctuations is of order , where
is the Hubble parameter during inflation, and we argue that this behavior is
generic, although by no means inevitable. With fixed boundary condition, we
find that the shape of the modulation to the power spectra is determined
entirely by the deviation of the background spacetime from the de Sitter limit.Comment: 15 pages (RevTeX), 2 figure
Enhancement of Non-Gaussianity after Inflation
We study the evolution of cosmological perturbations on large scales, up to
second order, for a perfect fluid with generic equation of state. Taking
advantage of super-horizon conservation laws, it is possible to follow the
evolution of the non-Gaussianity of perturbations through the different stages
after inflation. We find that a large non-linearity is generated by the
gravitational dynamics from the original inflationary quantum fluctuations.
This leads to a significant enhancement of the tiny intrinsic non-Gaussianity
produced during inflation in single-field slow-roll models.Comment: 12 pages, LaTeX file. Revised to match the final version accepted for
publication on JHE
Observational consequences of the Standard Model Higgs inflation variants
We consider the possibility to observationally differentiate the Standard
Model (SM) Higgs driven inflation with non-minimal couplingto gravity from
other variants of SM Higgs inflation based on the scalar field theories with
non-canonical kinetic term such as Galileon-like kinetic term and kinetic term
with non-minimal derivative coupling to the Einstein tensor. In order to ensure
consistent results, we study the SM Higgs inflation variants by using the same
method, computing the full dynamics of the background and perturbations of the
Higgs field during inflation at quantum level. Assuming that all the SM Higgs
inflation variants are consistent theories, we use the MCMC technique to derive
constraints on the inflationnoary parameters and the Higgs boson mass from
their fit to WMAP7+SN+BAO data set. We conclude that a combination of a Higgs
mass measurement by the LHC and accurate determination by the PLANCK satellite
of the spectral index of curvature perturbations and tensor-to-scalar ratio
will enable to distinguish among these models. We also show that the
consistency relations of the SM Higgs inflation variants are distinct enough to
differentiate the models.Comment: 22 pages, 4 figure
On the reheating stage after inflation
We point out that inflaton decay products acquire plasma masses during the
reheating phase following inflation. The plasma masses may render inflaton
decay kinematicaly forbidden, causing the temperature to remain frozen for a
period at a plateau value. We show that the final reheating temperature may be
uniquely determined by the inflaton mass, and may not depend on its coupling.
Our findings have important implications for the thermal production of
dangerous relics during reheating (e.g., gravitinos), for extracting bounds on
particle physics models of inflation from Cosmic Microwave Background
anisotropy data, for the production of massive dark matter candidates during
reheating, and for models of baryogenesis or leptogensis where massive
particles are produced during reheating.Comment: 8 pages, 2 figures. Submitted for publication in Phys. Rev.
On Thermalization in de Sitter Space
We discuss thermalization in de Sitter space and argue, from two different
points of view, that the typical time needed for thermalization is of order
, where is the radius of the de Sitter space in question.
This time scale gives plenty of room for non-thermal deviations to survive
during long periods of inflation. We also speculate in more general terms on
the meaning of the time scale for finite quantum systems inside isolated boxes,
and comment on the relation to the Poincar\'{e} recurrence time.Comment: 14 pages, 2 figures, latex, references added. Improved discussion in
section 3 adde
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