114 research outputs found
CMB Power Spectrum from Noncommutative Spacetime
Very recent CMB data of WMAP offers an opportunity to test inflation models,
in particular, the running of spectral index is quite new and can be used to
rule out some models. We show that an noncommutative spacetime inflation model
gives a good explanation of these new results. In fitting the data, we also
obtain a relationship between the noncommutative parameter (string scale) and
the ending time of inflation.Comment: 8 pages, 2 figures; v2: refs. added and minor corrections; v3:
further minor correctio
Inflation in Gauged 6D Supergravity
In this note we demonstrate that chaotic inflation can naturally be realized
in the context of an anomaly free minimal gauged supergravity in D=6 which has
recently been the focus of some attention. This particular model has a unique
maximally symmetric ground state solution, which leaves
half of the six-dimensional supersymmetries unbroken. In this model, the
inflaton field originates from the complex scalar fields in the D=6
scalar hypermultiplet. The mass and the self couplings of the scalar field are
dictated by the D=6 Lagrangian. The scalar potential has an absolute munimum at
with no undetermined moduli fields. Imposing a mild bound on the
radius of enables us to obtain chaotic inflation. The low eenrgy
equations of motion are shown to be consistent for the range of scalar field
values relevant for inflation.Comment: one reference adde
Moduli Instability in Warped Compactifications of the Type IIB Supergravity
We show that the conifold and deformed-conifold warped compactifications of
the ten-dimensional type IIB supergravity, including the Klebanov-Strassler
solution, are dynamically unstable in the moduli sector representing the scale
of a Calabi-Yau space, although it can be practically stable for a quite long
time in a region with a large warp factor. This instability is associated with
complete supersymmetry breaking except for a special case and produces
significant time-dependence in the structure of the four-dimensional base
spacetime as well as of the internal space.Comment: 24 pages, no figure. Typos corrected, and some arguments in section 5
are adde
The Energy Density of "Wound" Fields in a Toroidal Universe
The observational limits on the present energy density of the Universe allow
for a component that redshifts like and can contribute significantly to
the total. We show that a possible origin for such a contribution is that the
universe has a toroidal topology with "wound" scalar fields around its cycles.Comment: 11 pages, 1figur
High order correlation functions for self interacting scalar field in de Sitter space
We present the expressions of the three- and four-point correlation functions
of a self interacting light scalar field in a de Sitter spacetime at tree order
respectively for a cubic and a quartic potential. Exact expressions are derived
and their limiting behaviour on super-horizon scales are presented. Their
essential features are shown to be similar to those obtained in a classical
approach.Comment: 8 pages, 4 figure
Addendum to "Superimposed Oscillations in the WMAP Data?"
We elaborate further on the possibility that the inflationary primordial
power spectrum contains superimposed oscillations. We study various effects
which could influence the calculation of the multipole moments in this case. We
also present the theoretical predictions for two other cosmological
observables, the matter power spectrum and the EE polarization channel.Comment: 4 pages, 3 figures, uses RevTex4, matches published versio
Probing the primordial power spectra with inflationary priors
We investigate constraints on power spectra of the primordial curvature and
tensor perturbations with priors based on single-field slow-roll inflation
models. We stochastically draw the Hubble slow-roll parameters and generate the
primordial power spectra using the inflationary flow equations. Using data from
recent observations of CMB and several measurements of geometrical distances in
the late Universe, Bayesian parameter estimation and model selection are
performed for models that have separate priors on the slow-roll parameters. The
same analysis is also performed adopting the standard parameterization of the
primordial power spectra. We confirmed that the scale-invariant
Harrison-Zel'dovich spectrum is disfavored with increased significance from
previous studies. While current observations appear to be optimally modeled
with some simple models of single-field slow-roll inflation, data is not enough
constraining to distinguish these models.Comment: 23 pages, 3 figures, 7 tables, accepted for publication in JCA
Production of Massless Fermions during Inflation
We compute the one loop self energy, in a locally de Sitter background, for a
massless fermion which is Yukawa-coupled to a massless, minimally coupled
scalar. We then solve the modified Dirac equation resulting from inclusion of
the self energy. We find faster-than-exponential growth in the fermion wave
function, consistent with the production of fermions through a process in which
a scalar and a fermion-anti-fermion pair are ripped out of the vacuum by
inflation.Comment: 17 pages, LaTeX 2e, 1 figure. The first 15 pages gives the text of
version 1, which matches the published version. The erratum appended on page
15 corrects a crucial sign error which COMPLETELY CHANGES THE PHYSICAL
CONCLUSION
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
Non-minimally Coupled Tachyonic Inflation in Warped String Background
We show that the non-minimal coupling of tachyon field to the scalar
curvature, as proposed by Piao et al, with the chosen coupling parameter does
not produce the effective potential where the tachyon field can roll down from
T=0 to large along the slope of the potential. We find a correct choice of
the parameters which ensures this requirement and support slow-roll inflation.
However, we find that the cosmological parameter found from the analysis of the
theory are not in the range obtained from observations. We then invoke warped
compactification and varying dilaton field over the compact manifold, as
proposed by Raeymaekers, to show that in such a setup the observed parameter
space can be ensured.Comment: minor typos corrected and references adde
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