97 research outputs found
Wronskian Formulation of the Spectrum of Curvature Perturbations
We present a new formulation for the evaluation of the primordial spectrum of
curvature perturbations generated during inflation, using the fact that the
Wronskian of the scalar field perturbation equation is constant. In the
literature, there are many works on the same issue focusing on a few specific
aspects or effects. Here we deal with the general multi-component scalar field,
and show that our new formalism gives a method to evaluate the final amplitude
of the curvature perturbation systematically and economically. The advantage of
the new method is that one only has to solve a single mode of the scalar field
perturbation equation backward in time from the end of inflation to the stage
at which the perturbation is within the Hubble horizon, at which the initial
values of the scalar field perturbations are given. We also clarify the
relation of the new method with the new delta N formalism recently developed in
Lee et al.(2005).Comment: 13 pages, 1 figures, submitted to JCAP, Minor corrections have been
mad
Gravitational wave background as a probe of the primordial black hole abundance
Formation of significant number of primordial black holes (PBHs) is realized
if and only if primordial density fluctuations have a large amplitude, which
means that tensor perturbations generated from these scalar perturbations as a
second order effect are also large and comparable to the observational data. We
show that pulsar timing observation could find/rule out PBHs with \sim 10^2
M_solar which are considered as a candidate of intermediate-mass black holes
and that PBHs with mass range 10^{20-26} g, which serves as a candidate of dark
matter, may be probed by future space-based laser interferometers and atomic
interferometers.Comment: 4 pages, 2 figure
What happens when the inflaton stops during inflation
The spectrum of adiabatic density perturbation generated during inflation is
studied in the case the time derivative of an inflation-driving scalar field
(inflaton) vanishes at some time during inflation. It is shown that the
nondecaying mode of perturbation has a finite value even in this case and that
its amplitude is given by the standard formula with the time derivation of the
scalar field replaced by the potential gradient using the slow-roll equation
New inflation in supergravity with a chaotic initial condition
We propose a self-consistent scenario of new inflation in supergravity.
Chaotic inflation first takes place around the Planck scale, which solves the
longevity problem, namely, why the universe can live much beyond the Planck
time, and also gives an adequate initial condition for new inflation. Then, new
inflation lasts long enough to generate primordial fluctuations for the large
scale structure, which generally has a tilted spectrum with the spectral index
. The successive decay of the inflaton leads to the reheating
temperature low enough to avoid the overproduction of gravitinos in a wide
range of the gravitino mass.Comment: 11 pages. To appear in Phys. Rev.
A New delta N Formalism for Multi-Component Inflation
The delta N formula that relates the final curvature perturbation on comoving
slices to the inflaton perturbation on flat slices after horizon crossing is a
powerful and intuitive tool to compute the curvature perturbation spectrum from
inflation. However, it is customarily assumed further that the conventional
slow-roll condition is satisfied, and satisfied by all components, during
horizon crossing. In this paper, we develop a new delta N formalism for
multi-component inflation that can be applied in the most general situations.
This allows us to generalize the idea of general slow-roll inflation to the
multi-component case, in particular only applying the general slow-roll
condition to the relevant component. We compute the power spectrum of the
curvature perturbation in multi-component general slow-roll inflation, and find
that under quite general conditions it is invertible.Comment: 24 pages, no figur
Scale-invariance in expanding and contracting universes from two-field models
We study cosmological perturbations produced by the most general
two-derivative actions involving two scalar fields, coupled to Einstein
gravity, with an arbitrary field space metric, that admit scaling solutions.
For contracting universes, we show that scale-invariant adiabatic perturbations
can be produced continuously as modes leave the horizon for any equation of
state parameter . The corresponding background solutions are unstable,
which we argue is a universal feature of contracting models that yield
scale-invariant spectra. For expanding universes, we find that nearly
scale-invariant adiabatic perturbation spectra can only be produced for , and that the corresponding scaling solutions are attractors. The
presence of a nontrivial metric on field space is a crucial ingredient in our
results.Comment: 23 pages, oversight in perturbations calculation corrected,
conclusions for expanding models modifie
Extended Curvaton reheating in inflationary models
The curvaton reheating in a non-oscillatory inflationary universe model is
studied in a Jordan-Brans-Dicke theory. For different scenarios, the
temperature of reheating is computed. The result tells us that the reheating
temperature becomes practically independent of the Jordan-Brans-Dicke parameter
. This reheating temperature results to be quite different when compared
with that obtained from Einstein`s theory of gravity.Comment: Accepted by JCAP, 12 pages, 1 Figur
Curvature and isocurvature perturbations in two-field inflation
We study cosmological perturbations in two-field inflation, allowing for non-standard kinetic terms. We calculate analytically the spectra of curvature and isocurvature modes at Hubble crossing, up to first order in the slow-roll parameters. We also compute numerically the evolution of the curvature and isocurvature modes from well within the Hubble radius until the end of inflation. We show explicitly for a few examples, including the recently proposed model of ârouletteâ inflation, how isocurvature perturbations affect significantly the curvature perturbation between Hubble crossing and the end of inflation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/58173/2/jcap7_07_014.pd
Supergravity based inflation models: a review
In this review, we discuss inflation models based on supergravity. After
explaining the difficulties in realizing inflation in the context of
supergravity, we show how to evade such difficulties. Depending on types of
inflation, we give concrete examples, particularly paying attention to chaotic
inflation because the ongoing experiments like Planck might detect the tensor
perturbations in near future. We also discuss inflation models in Jordan frame
supergravity, motivated by Higgs inflation.Comment: 30 pages, invited review for Classical and Quantum Gravity, published
versio
Classicality of primordial fluctuations and Primordial Black Holes
The production of Primordial Black Holes (PBH) from inflationary
perturbations provides a physical process where the effective classicality of
the fluctuations does not hold for certain scales. For adiabatic perturbations
produced during inflation, this range of scales corresponds to PBH with masses
g. For PBH with masses , the horizon mass at the
end of inflation, the generation process during the preheating stage could be
classical as well, in contrast to the formation of PBH on these scales by
adiabatic inflationary perturbations. For the non evaporated PBH, the
generation process is essentially classical.Comment: uses LaTeX, 8 pages; one ref. added; to appear in Int. J. of Mod.
Physics
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