45 research outputs found

### Right-handed neutrinos as the source of density perturbations

We study the possibility that cosmological density perturbations are
generated by the inhomogeneous decay of right-handed neutrinos. This will occur
if a scalar field whose fluctuations are created during inflation is coupled to
the neutrino sector. Robust predictions of the model are a detectable level of
non-Gaussianity and, if standard leptogenesis is the source of the baryon
asymmetry, a baryon isocurvature perturbations at the level of the present
experimental constraints.Comment: 14 pages, 2 figure

### Phenomenological approaches of inflation and their equivalence

In this work, we analyze two possible alternative and model-independent
approaches to describe the inflationary period. The first one assumes a general
equation of state during inflation due to Mukhanov, while the second one is
based on the slow-roll hierarchy suggested by Hoffman and Turner. We find that,
remarkably, the two approaches are equivalent from the observational viewpoint,
as they single out the same areas in the parameter space, and agree with the
inflationary attractors where successful inflation occurs. Rephrased in terms
of the familiar picture of a slowly rolling, canonically normalized scalar
field, the resulting inflaton excursions in these two approaches are almost
identical. Furthermore, once the Galactic dust polarization data from Planck
are included in the numerical fits, inflaton excursions can safely take
sub-Planckian values.Comment: Revtex, 8 pages, 4 figures. References updated. Matches published
version in PR

### The degenerate gravitino scenario

In this work, we explore the "degenerate gravitino" scenario where the mass
difference between the gravitino and the lightest MSSM particle is much smaller
than the gravitino mass itself. In this case, the energy released in the decay
of the next to lightest sypersymmetric particle (NLSP) is reduced. Consequently
the cosmological and astrophysical constraints on the gravitino abundance, and
hence on the reheating temperature, become softer than in the usual case. On
the other hand, such small mass splittings generically imply a much longer
lifetime for the NLSP. We find that, in the constrained MSSM (CMSSM), for
neutralino LSP or NLSP, reheating temperatures compatible with thermal
leptogenesis are reached for small splittings of order 10^{-2} GeV. While for
stau NLSP, temperatures of 4x10^9 GeV can be obtained even for splittings of
order of tens of GeVs. This "degenerate gravitino" scenario offers a possible
way out to the gravitino problem for thermal leptogenesis in supersymmetric
theories.Comment: 27 pages, 10 figures and 1 table. Minor typos and references fixed.
Matches published version in JCAP

### Model-independent fit to Planck and BICEP2 data

Inflation is the leading theory to describe elegantly the initial conditions that led to structure formation in our Universe. In this paper, we present a novel phenomenological fit to the Planck, WMAP polarization (WP) and the BICEP2 data sets using an alternative parametrization. Instead of starting from inflationary potentials and computing the inflationary observables, we use a phenomenological parametrization due to Mukhanov, describing inflation by an effective equation of state, in terms of the number of e-folds and two phenomenological parameters alpha and beta. Within such a parametrization, which captures the different inflationary models in a model-independent way, the values of the scalar spectral index n(s), its running and the tensor-to-scalar ratio r are predicted, given a set of parameters (alpha, beta). We perform a Markov Chain Monte Carlo analysis of these parameters, and we show that the combined analysis of Planck and WP data favors the Starobinsky and Higgs inflation scenarios. Assuming that the BICEP2 signal is not entirely due to foregrounds, the addition of this last data set prefers instead the phi(2) chaotic models. The constraint we get from Planck and WP data alone on the derived tensor-to-scalar ratio is r < 0.18 at 95% C.L., value which is consistent with the one quoted from the BICEP2 Collaboration analysis, r = 0.16(-0.05)(+0-06), after foreground subtraction. This is not necessarily at odds with the 2 sigma tension found between Planck and BICEP2 measurements when analyzing data in terms of the usual n(s) and r parameters, given that the parametrization used here, for the preferred value n(s) similar or equal to 0.96, allows only for a restricted parameter space in the usual (n(s), r) plane

### Sachs-Wolfe at second order: the CMB bispectrum on large angular scales

We calculate the Cosmic Microwave Background anisotropy bispectrum on large
angular scales in the absence of primordial non-Gaussianities, assuming exact
matter dominance and extending at second order the classic Sachs-Wolfe result
\delta T/T=\Phi/3. The calculation is done in Poisson gauge. Besides intrinsic
contributions calculated at last scattering, one must consider integrated
effects. These are associated to lensing, and to the time dependence of the
potentials (Rees-Sciama) and of the vector and tensor components of the metric
generated at second order. The bispectrum is explicitly computed in the
flat-sky approximation. It scales as l^(-4) in the scale invariant limit and
the shape dependence of its various contributions is represented in 3d plots.
Although all the contributions to the bispectrum are parametrically of the same
order, the full bispectrum is dominated by lensing. In the squeezed limit it
corresponds to f_NL^local = -1/6 - cos(2 \theta), where \theta is the angle
between the short and the long modes; the angle dependent contribution comes
from lensing. In the equilateral limit it corresponds to f_NL^equil ~ 3.13.Comment: 38 pages, 9 figures. v2: minor corrections to match published versio