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

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 $\rho^2$ terms, where $\rho$ 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 $\rho^2$ 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

High-Energy theory for close Randall Sundrum branes

We obtain an effective theory for the radion dynamics of the two-brane Randall Sundrum model, correct to all orders in brane velocity in the limit of close separation, which is of interest for studying brane collisions and early Universe cosmology. Obtained via a recursive solution of the Bulk equation of motions, the resulting theory represents a simple extension of the corresponding low-energy effective theory to the high energy regime. The four-dimensional low-energy theory is indeed not valid when corrections at second order in velocity are considered. This extension has the remarkable property of including only second derivatives and powers of first order derivatives. This important feature makes the theory particularly easy to solve. We then extend the theory by introducing a potential and detuning the branes.Comment: Version published in the Physical Review

Cosmological CMBR dipole in open universes ?

The observed CMBR dipole is generally interpreted as a Doppler effect arising from the motion of the Earth relative to the CMBR frame. An alternative interpretation, proposed in the last years, is that the dipole results from ultra-large scale isocurvature perturbations. We examine this idea in the context of open cosmologies and show that the isocurvature interpretation is not valid in an open universe, unless it is extremely close to a flat universe, $|\Omega_0 -1|< 10^{-4}$.Comment: 26 pages, Latex, 6 figures, to appear in Phys. Rev.

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

Light wino dark matter in brane world cosmology

The thermal relic density of the wino-like neutralino dark matter in the brane world cosmology is studied. The expansion law at a high energy regime in the brane world cosmology is modified from the one in the standard cosmology, and the resultant relic density can be enhanced if the five dimensional Planck mass $M_5$ is low enough. We calculate the wino-like neutralino relic density in the anomaly mediated supersymmetry breaking scenario and show that the allowed region is dramatically modified from the one in the standard cosmology and the wino-like neutralino with mass of order 100 GeV can be a good candidate for the dark matter. Since the allowed region disappears eventually as $M_5$ is decreasing, we can find a lower bound on $M_5 \gtrsim 100$ TeV according to the neutralino dark matter hypothesis, namely the lower bound in order for the allowed region of the neutralino dark matter to exist.Comment: 16 pages, 9 figures, final versio