28 research outputs found
Generating the curvature perturbation at the end of inflation
The dominant contribution to the primordial curvature perturbation may be
generated at the end of inflation. Taking the end of inflation to be sudden,
formulas are presented for the spectrum, spectral tilt and non-gaussianity.
They are evaluated for a minimal extension of the original hybrid inflation
model.Comment: 5 pages. v3: as it will appear in JCA
Contribution of the hybrid inflation waterfall to the primordial curvature perturbation
A contribution to the curvature perturbation will be generated
during the waterfall that ends hybrid inflation, that may be significant on
small scales. In particular, it may lead to excessive black hole formation. We
here consider standard hybrid inflation, where the tachyonic mass of the
waterfall field is much bigger than the Hubble parameter. We calculate
in the simplest case, and see why earlier calculations of
are incorrect.Comment: Simpler and more complete results, especiallly for delta N approac
On the Issue of the \zeta Series Convergence and Loop Corrections in the Generation of Observable Primordial Non-Gaussianity in Slow-Roll Inflation. Part II: the Trispectrum
We calculate the trispectrum T_\zeta of the primordial curvature perturbation
\zeta, generated during a {\it slow-roll} inflationary epoch by considering a
two-field quadratic model of inflation with {\it canonical} kinetic terms. We
consider loop contributions as well as tree level terms, and show that it is
possible to attain very high, {\it including observable}, values for the level
of non-gaussianity \tau_{NL} if T_\zeta is dominated by the one-loop
contribution. Special attention is paid to the claim in JCAP {\bf 0902}, 017
(2009) [arXiv:0812.0807 [astro-ph]] that, in the model studied in this paper
and for the specific inflationary trajectory we choose, the quantum
fluctuations of the fields overwhelm the classical evolution. We argue that
such a claim actually does not apply to our model, although more research is
needed in order to understand the role of quantum diffusion. We also consider
the probability that an observer in an ensemble of realizations of the density
field sees a non-gaussian distribution. In that respect, we show that the
probability associated to the chosen inflationary trajectory is non-negligible.
Finally, the levels of non-gaussianity f_{NL} and \tau_{NL} in the bispectrum
B_\zeta and trispectrum T_\zeta of \zeta, respectively, are also studied for
the case in which \zeta is not generated during inflation.Comment: LaTex File, 27 pages, 8 figures. v2: Previous Section 2 has been
removed. Two new sections (3 and 4) discussing the classicality condition
given by Byrnes, Choi, and Hall, in JCAP 0902, 017 (2009), and the
probability that an observer sees a non-gaussian distribution have been
added. v3: Version accepted for publication in Physical Review
Comments on SUSY inflation models on the brane
In this paper we consider a class of inflation models on the brane where the
dominant part of the inflaton scalar potential does not depend on the inflaton
field value during inflation. In particular, we consider supernatural
inflation, its hilltop version, A-term inflation, and supersymmetric (SUSY) D-
and F-term hybrid inflation on the brane. We show that the parameter space can
be broadened, the inflation scale generally can be lowered, and still possible
to have the spectral index .Comment: 7 page
A semi-analytical approach to perturbations in mutated hilltop inflation
We study cosmological perturbations and observational aspects for mutated
hilltop model of inflation. Employing mostly analytical treatment, we evaluate
observable parameters during inflation as well as post-inflationary
perturbations. This further leads to exploring observational aspects related to
Cosmic Microwave Background (CMB) radiation. This semi-analytical treatment
reduces complications related to numerical computation to some extent for
studying the different phenomena related to CMB angular power spectrum for
mutated hilltop inflation.Comment: 7 pages, 2 figures. Improved version to appear in IJMP
CMB Anisotropies at Second Order I
We present the computation of the full system of Boltzmann equations at
second-order describing the evolution of the photon, baryon and cold dark
matter fluids. These equations allow to follow the time evolution of the Cosmic
Microwave Background (CMB) anisotropies at second-order at all angular scales
from the early epoch, when the cosmological perturbations were generated, to
the present through the recombination era. This paper sets the stage for the
computation of the full second-order radiation transfer function at all scales
and for a a generic set of initial conditions specifying the level of
primordial non-Gaussianity. In a companion paper, we will present the
computation of the three-point correlation function at recombination which is
so relevant for the issue of non-Gaussianity in the CMB anisotropies.Comment: 26 pages, LaTeX file, typos correcte
Non-Gaussianity in Multi-field Stochastic Inflation with the Scaling Approximation
The statistics of multi-field inflation are investigated using the stochastic
approach. We analytically obtain the probability distribution function of
fields with the scaling approximation by extending the previous work by
Amendola. The non-Gaussian nature of the probability distribution function is
investigated decomposing the fields into the adiabatic and isocurvature
components. We find that the non-Gaussianity of the isocurvature component can
be large compared with that of the adiabatic component. The adiabatic and
isocurvature components may be correlated at nonlinear order in the skewness
and kurtosis even if uncorrelated at linear level.Comment: To appear in JCAP, references adde
The Lyth Bound and the End of Inflation
We derive an extended version of the well-known Lyth Bound on the total
variation of the inflaton field, incorporating higher order corrections in slow
roll. We connect the field variation to both the spectral index of
scalar perturbations and the amplitude of tensor modes. We then investigate the
implications of this bound for ``small field'' potentials, where the field
rolls off a local maximum of the potential. The total field variation during
inflation is {\em generically} of order , even for potentials with
a suppressed tensor/scalar ratio. Much of the total field excursion arises in
the last e-fold of inflation and in single field models this problem can only
be avoided via fine-tuning or the imposition of a symmetry. Finally, we discuss
the implications of this result for inflationary model building in string
theory and supergravity.Comment: 10 pages, RevTeX, 2 figures (V3: version accepted for publication by
JCAP
On the Issue of the \zeta Series Convergence and Loop Corrections in the Generation of Observable Primordial Non-Gaussianity in Slow-Roll Inflation. Part I: the Bispectrum
We show in this paper that it is possible to attain very high, {\it including
observable}, values for the level of non-gaussianity f_{NL} associated with the
bispectrum B_\zeta of the primordial curvature perturbation \zeta, in a
subclass of small-field {\it slow-roll} models of inflation with canonical
kinetic terms. Such a result is obtained by taking care of loop corrections
both in the spectrum P_\zeta and the bispectrum B_\zeta. Sizeable values for
f_{NL} arise even if \zeta is generated during inflation. Five issues are
considered when constraining the available parameter space: 1. we must ensure
that we are in a perturbative regime so that the \zeta series expansion, and
its truncation, are valid. 2. we must apply the correct condition for the
(possible) loop dominance in B_\zeta and/or P_\zeta. 3. we must satisfy the
spectrum normalisation condition. 4. we must satisfy the spectral tilt
constraint. 5. we must have enough inflation to solve the horizon problem.Comment: LaTeX file, 40 pages, 6 figures, Main body: 26 pages, Appendix: 8
pages, References: 6 pages. v2: minor grammatical changes, references added
and updated, a few changes reflecting the fact that = 0, conclusions
unchanged. Version accepted for publication in Journal of Cosmology and
Astroparticle Physic
Large Nongaussianity from Nonlocal Inflation
We study the possibility of obtaining large nongaussian signatures in the
Cosmic Microwave Background in a general class of single-field nonlocal
hill-top inflation models. We estimate the nonlinearity parameter f_{NL} which
characterizes nongaussianity in such models and show that large nongaussianity
is possible. For the recently proposed p-adic inflation model we find that
f_{NL} ~ 120 when the string coupling is order unity. We show that large
nongaussianity is also possible in a toy model with an action similar to those
which arise in string field theory.Comment: 27 pages, no figures. Added references and some clarifying remark