2,655 research outputs found
Generalized Slow Roll Conditions and the Possibility of Intermediate Scale Inflation in Scalar-Tensor Theory
Generalized slow roll conditions and parameters are obtained for a general
form of scalar-tensor theory (with no external sources), having arbitrary
functions describing a nonminimal gravitational coupling F(\phi), a Kahler-like
kinetic function k(\phi), and a scalar potential V(\phi). These results are
then used to analyze a simple toy model example of chaotic inflation with a
single scalar field \phi and a standard Higgs potential and a simple
gravitational coupling function. In this type of model inflation can occur with
inflaton field values at an intermediate scale of roughly 10^{11} GeV when the
particle physics symmetry breaking scale is approximately 1 TeV, provided that
the theory is realized within the Jordan frame. If the theory is realized in
the Einstein frame, however, the intermediate scale inflation does not occur.Comment: 14 pages, no figs. Accepted to Classical and Quantum Gravit
D-term chaotic inflation in supergravity
Even though the chaotic inflation is one of the most popular inflation models
for its simple dynamics and compelling resolutions to the initial condition
problems, its realization in supergravity has been considered a challenging
task. We discuss how the chaotic inflation dominated by the D-term can be
induced in supergravity, which would give a new perspective on the inflation
model building in supergravity.Comment: 5 pages, to appear in Phys. Rev.
Can Inflation be Falsified?
Despite its central role in modern cosmology, doubts are often expressed as
to whether cosmological inflation is really a falsifiable theory. We
distinguish two facets of inflation, one as a theory of initial conditions for
the hot big bang and the other as a model for the origin of structure in the
Universe. We argue that the latter can readily be excluded by observations, and
that there are also a number of ways in which the former can find itself in
conflict with observational data. Both aspects of the theory are indeed
falsifiable.Comment: 7 pages LaTeX file with two figures incorporated by epsf. Fifth Prize
in Gravity Research Foundation Essay Competition. To appear, General
Relativity and Gravitatio
Intermediate inflation in light of the three-year WMAP observations
The three-year observations from the Wilkinson Microwave Anisotropy Probe
have been hailed as giving the first clear indication of a spectral index
n_s<1. We point out that the data are equally well explained by retaining the
assumption n_s=1 and allowing the tensor-to-scalar ratio r to be non-zero. The
combination n_s=1 and r>0 is given (within the slow-roll approximation) by a
version of the intermediate inflation model with expansion rate H(t) \propto
t^{-1/3}. We assess the status of this model in light of the WMAP3 data.Comment: 4 pages RevTeX4 with one figure. Minor changes to match PRD accepted
versio
False Vacuum Inflation with a Quartic Potential
We consider a variant of Hybrid Inflation, where inflation is driven by two
interacting scalar fields, one of which has a `Mexican hat' potential and the
other a quartic potential. Given the appropriate initial conditions one of the
fields can be trapped in a false vacuum state, supported by couplings to the
other field. The energy of this vacuum can be used to drive inflation, which
ends when the vacuum decays to one of its true minima. Depending on parameters,
it is possible for inflation to proceed via two separate epochs, with the
potential temporarily steepening sufficiently to suspend inflation. We use
numerical simulations to analyse the possibilities, and emphasise the
shortcomings of the slow-roll approximation for analysing this scenario. We
also calculate the density perturbations produced, which can have a spectral
index greater than one.Comment: 10 pages, RevTeX 3.0, no figure
Coleman-Weinberg Potential In Good Agreement With WMAP
We briefly summarize and update a class of inflationary models from the early
eighties based on a quartic (Coleman-Weinberg) potential for a gauge singlet
scalar (inflaton) field. For vacuum energy scales comparable to the grand
unification scale, the scalar spectral index n_s=0.94-0.97, in very good
agreement with the WMAP three year results. The tensor to scalar ratio r<~0.14,
while alpha=dn/dlnk is =~-10^-3. An SO(10) version naturally explains the
observed baryon asymmetry via non-thermal leptogenesis.Comment: v1: 6 pages, 1 table. v2: minor corrections. v3: 8 pages, added some
details, comments, references and 3 figures. v4: minor corrections, published
versio
Must Cosmological Perturbations Remain Non-Adiabatic After Multi-Field Inflation?
Even if non-adiabatic perturbations are generated in multi-field inflation,
the perturbations will become adiabatic if the universe after inflation enters
an era of local thermal equilibrium, with no non-zero conserved quantities, and
will remain adiabatic as long as the wavelength is outside the horizon, even
when local thermal equilibrium no longer applies. Small initial non-adiabatic
perturbations associated with imperfect local thermal equilibrium remain small
when baryons are created from out-of-equilibrium decay of massive particles, or
when dark matter particles go out of local thermal equilibrium.Comment: 12 pages, typographical errors corrected, acknowledgment added.
Article accepted for publication in Physical Review
Cosmic microwave background constraints on the epoch of reionization
We use a compilation of cosmic microwave anisotropy data to constrain the
epoch of reionization in the Universe, as a function of cosmological
parameters. We consider spatially-flat cosmologies, varying the matter density
(the flatness being restored by a cosmological constant), the Hubble
parameter and the spectral index of the primordial power spectrum. Our
results are quoted both in terms of the maximum permitted optical depth to the
last-scattering surface, and in terms of the highest allowed reionization
redshift assuming instantaneous reionization. For critical-density models,
significantly-tilted power spectra are excluded as they cannot fit the current
data for any amount of reionization, and even scale-invariant models must have
an optical depth to last scattering of below 0.3. For the currently-favoured
low-density model with and a cosmological constant, the
earliest reionization permitted to occur is at around redshift 35, which
roughly coincides with the highest estimate in the literature. We provide
general fitting functions for the maximum permitted optical depth, as a
function of cosmological parameters. We do not consider the inclusion of tensor
perturbations, but if present they would strengthen the upper limits we quote.Comment: 9 pages LaTeX file with ten figures incorporated (uses mn.sty and
epsf). Corrects some equation typos, superseding published versio
Non-Gaussianity in the modulated reheating scenario
We investigate the non-Gaussianity of primordial curvature perturbation in
the modulated reheating scenario where the primordial perturbation is generated
due to the spacial fluctuation of the inflaton decay rate to radiation. We use
the formalism to evaluate the trispectrum of curvature perturbation
as well as its bispectrum. We give expressions for three non-linear parameters
and in the modulated reheating scenario. If the
intrinsic non-Gaussianity of scalar field fluctuations and third derivative of
the decay rate with respect to scalar fields are negligibly small, has
at least the same order of magnitude as . We also give general
inequality between and which is true for other
inflationary scenarios as long as primordial non-Gaussianity comes from
super-horizon evolution.Comment: references adde
Extended Inflation with a Curvature-Coupled Inflaton
We examine extended inflation models enhanced by the addition of a coupling
between the inflaton field and the space-time curvature. We examine two types
of model, where the underlying inflaton potential takes on second-order and
first-order form respectively. One aim is to provide models which satisfy the
solar system constraints on the Brans--Dicke parameter . This
constraint has proven very problematic in previous extended inflation models,
and we find circumstances where it can be successfully evaded, though the
constraint must be carefully assessed in our model and can be much stronger
than the usual . In the simplest versions of the model, one may
avoid the need to introduce a mass for the Brans--Dicke field in order to
ensure that it takes on the correct value at the present epoch, as seems to be
required in hyperextended inflation. We also briefly discuss aspects of the
formation of topological defects in the inflaton field itself.Comment: 24 pages, LaTeX (no figures), to appear, Physical Review D,
mishandling of the solar system constraint on extended gravity theories
corrected, SUSSEX-AST 93/6-
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