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

Frequentist analyses of solar neutrino data (updated including KamLAND and SNO data)

The solar neutrino data are analyzed in a frequentist framework, using the Crow-Gardner and Feldman-Cousins prescriptions for the construction of confidence regions. Including in the fit only the total rates measured by the various experiments, both methods give results similar to the commonly used Delta chi^2-cut approximation. When fitting the full data set, the Delta chi^2-cut still gives a good approximation of the Feldman-Cousins regions. However, a careful statistical analysis significantly reduces the goodness-of-fit of the SMA and LOW solutions. In the addenda we discuss the implications of the latest KamLAND, SNO and SK data.Comment: 24 pages, 12 figures. Version 2: addendum about the CC SNO data (section 6). Version 3: addendum about the NC and day/night SNO data (section 7). Version 4: addendum about the KamLAND data (section 8). Version 5: addendum about SNO salt data (section 9, pages 22, 23). Version 6: final addendum about final SNO salt data and KamLAND (section 10, page 24

Galilean Genesis: an alternative to inflation

We propose a novel cosmological scenario, in which standard inflation is replaced by an expanding phase with a drastic violation of the Null Energy Condition (NEC): \dot H >> H^2. The model is based on the recently introduced Galileon theories, that allow NEC violating solutions without instabilities. The unperturbed solution describes a Universe that is asymptotically Minkowski in the past, expands with increasing energy density until it exits the regime of validity of the effective field theory and reheats. This solution is a dynamical attractor and the Universe is driven to it, even if it is initially contracting. The study of perturbations of the Galileon field reveals some subtleties, related to the gross violation of the NEC and it shows that adiabatic perturbations are cosmologically irrelevant. The model, however, suggests a new way to produce a scale invariant spectrum of isocurvature perturbations, which can later be converted to adiabatic: the Galileon is forced by symmetry to couple to the other fields as a dilaton; the effective metric it yields on the NEC violating solution is that of de Sitter space, so that all light scalars will automatically acquire a nearly scale-invariant spectrum of perturbations.Comment: 25 pages, 1 figure. v2: minor changes, JCAP published versio

Resilience of the standard predictions for primordial tensor modes

We show that the prediction for the primordial tensor power spectrum cannot be modified at leading order in derivatives. Indeed, one can always set to unity the speed of propagation of gravitational waves during inflation by a suitable disformal transformation of the metric, while a conformal one can make the Planck mass time-independent. Therefore, the tensor amplitude unambiguously fixes the energy scale of inflation. Using the Effective Field Theory of Inflation, we check that predictions are independent of the choice of frame, as expected. The first corrections to the standard prediction come from two parity violating operators with three derivatives. Also the correlator $$ is standard and only receives higher derivative corrections. These results hold also in multifield models of inflation and in alternatives to inflation and make the connection between a (quasi) scale-invariant tensor spectrum and inflation completely robust.Comment: 5 pages, reference added, version accepted in PR

Consistency Relations for the Conformal Mechanism

We systematically derive the consistency relations associated to the non-linearly realized symmetries of theories with spontaneously broken conformal symmetry but with a linearly-realized de Sitter subalgebra. These identities relate (N+1)-point correlation functions with a soft external Goldstone to N-point functions. These relations have direct implications for the recently proposed conformal mechanism for generating density perturbations in the early universe. We study the observational consequences, in particular a novel one-loop contribution to the four-point function, relevant for the stochastic scale-dependent bias and CMB mu-distortion.Comment: 34 pages, 3 figures. v2: minor changes, version appearing in JCA