4,166 research outputs found
Non-Gaussianities from isocurvature modes
This contribution discusses isocurvature modes, in particular the
non-Gaussianities of local type generated by these modes. Since the
isocurvature transfer functions differ from the adiabatic one, the coexistence
of a primordial isocurvature mode with the usual adiabatic mode leads to a rich
structure of the angular bispectrum, which can be decomposed into six
elementary bispectra. Future analysis of the CMB data will enable to measure
their relative weights, or at least constrain them. Non-Gaussianity thus
provides a new window on isocurvature modes. This is particularly relevant for
some scenarios, such as those presented here, which generate isocurvature modes
whose contribution in the power spectrum is suppressed, as required by present
data, but whose contribution in the non-Gaussianities could be dominant and
measurable.Comment: 8 pages, 2 figures; to appear in the Proceedings of COSGRAV-2012
(International Conference on Modern Perspectives of Cosmology and
Gravitation), Indian Statistical Institute, Kolkata, India, February 7-11,
201
General treatment of isocurvature perturbations and non-Gaussianities
We present a general formalism that provides a systematic computation of the
linear and non-linear perturbations for an arbitrary number of cosmological
fluids in the early Universe going through various transitions, in particular
the decay of some species (such as a curvaton or a modulus). Using this
formalism, we revisit the question of isocurvature non-Gaussianities in the
mixed inflaton-curvaton scenario and show that one can obtain significant
non-Gaussianities dominated by the isocurvature mode while satisfying the
present constraints on the isocurvature contribution in the observed power
spectrum. We also study two-curvaton scenarios, taking into account the
production of dark matter, and investigate in which cases significant
non-Gaussianities can be produced.Comment: Substantial improvements with respect to the first version. In
particular, we added a discussion on the confrontation of the models with
future observational data. This version is accepted for publication in JCA
Hunting for Isocurvature Modes in the CMB non-Gaussianities
We investigate new shapes of local primordial non-Gaussianities in the CMB.
Allowing for a primordial isocurvature mode along with the main adiabatic one,
the angular bispectrum is in general a superposition of six distinct shapes:
the usual adiabatic term, a purely isocurvature component and four additional
components that arise from correlations between the adiabatic and isocurvature
modes. We present a class of early Universe models in which various hierarchies
between these six components can be obtained, while satisfying the present
upper bound on the isocurvature fraction in the power spectrum. Remarkably,
even with this constraint, detectable non-Gaussianity could be produced by
isocurvature modes. We finally discuss the prospects of detecting these new
shapes with the Planck satellite.Comment: 9 pages, 2 figure
Massive scalar states localized on a de Sitter brane
We consider a brane scenario with a massive scalar field in the
five-dimensional bulk. We study the scalar states that are localized on the
brane, which is assumed to be de Sitter. These localized scalar modes are
massive in general, their effective four-dimensional mass depending on the mass
of the five-dimensional scalar field, on the Hubble parameter in the brane and
on the coupling between the brane tension and the bulk scalar field. We then
introduce a purely four-dimensional approach based on an effective potential
for the projection of the scalar field in the brane, and discuss its regime of
validity. Finally, we explore the quasi-localized scalar states, which have a
non-zero width that quantifies their probability of tunneling from the brane
into the bulk.Comment: 14 pages; 5 figure
Reheating and gravitino production in braneworld inflation
We consider the constraints that can be imposed on a wide class of Inflation
models in modified gravity scenarios in which the Friedmann equation is
modified by the inclusion of terms, where is the total energy
density. In particular we obtain the reheating temperature and gravitino
abundance associated with the end of inflation. Whereas models of chaotic
inflation and natural inflation can easily avoid the conventional gravitino
overproduction problem, we show that supersymmetric hybrid inflation models
(driven by both F and D-terms) do not work in the dominated era. We
also study inflation driven by exponetial potentials in this modified
background, and show that the gravitino production is suppressed enough to
avoid there being a problem, although other conditions severely constrain these
models.Comment: 24page
Scalar Kaluza-Klein modes in a multiply warped braneworld
The Kaluza-Klein (KK) modes of a massive scalar field on a 3-brane embedded
in six dimensional multiply warped spacetime are determined. Due to the
presence of warping along both the extra dimensions the KK mass spectrum splits
into two closely spaced branches which is a distinct feature of this model
compared to the five dimensional Randall-Sundrum model. This new cluster of the
KK mode spectrum is expected to have interesting phenomenological implications
for the upcoming collider experiments. Such a scenario may also be extended for
even larger number of orbifolded extra dimensions.Comment: 10 pages, Revte
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