Sergio Pastor

Massive neutrinos and cosmology

The present experimental results on neutrino flavour oscillations provide evidence for non-zero neutrino masses, but give no hint on their absolute mass scale, which is the target of beta decay and neutrinoless double-beta decay experiments. Crucial complementary information on neutrino masses can be obtained from the analysis of data on cosmological observables, such as the anisotropies of the cosmic microwave background or the distribution of large-scale structure. In this review we describe in detail how free-streaming massive neutrinos affect the evolution of cosmological perturbations. We summarize the current bounds on the sum of neutrino masses that can be derived from various combinations of cosmological data, including the most recent analysis by the WMAP team. We also discuss how future cosmological experiments are expected to be sensitive to neutrino masses well into the sub-eV range.

Relic neutrino decoupling including flavour oscillations

Abstract In the early universe, neutrinos are slightly coupled when electron–positron pairs annihilate transferring their entropy to photons. This process originates non-thermal distortions on the neutrino spectra which depend on neutrino flavour, larger for ν e than for ν μ or ν τ . We study the effect of three-neutrino flavour oscillations on the process of neutrino decoupling by solving the momentum-dependent kinetic equations for the neutrino spectra. We find that oscillations do not essentially modify the total change in the neutrino energy density, giving N eff = 3.046 in terms of the effective number of neutrinos, while the small effect over the production of primordial 4 He is increased by O ( 20 % ) , up to 2.1 × 10 −4 . These results are stable within the presently favoured region of neutrino mixing parameters.

Cosmological bounds on neutrino degeneracy improved by flavor oscillations

Abstract We study three-flavor neutrino oscillations in the early universe in the presence of neutrino chemical potentials. We take into account all effects from the background medium, i.e., collisional damping, the refractive effects from charged leptons, and in particular neutrino self-interactions that synchronize the neutrino oscillations. We find that effective flavor equilibrium between all active neutrino species is established well before the big-bang nucleosynthesis (BBN) epoch if the neutrino oscillation parameters are in the range indicated by the atmospheric neutrino data and by the large mixing angle (LMA) MSW solution of the solar neutrino problem. For the other solutions of the solar neutrino problem, partial flavor equilibrium may be achieved if the angle θ13 is close to the experimental limit tan2θ13≲0.065. In the LMA case, the BBN limit on the νe degeneracy parameter, |ξν|≲0.07, now applies to all flavors. Therefore, a putative extra cosmic radiation contribution from degenerate neutrinos is limited to such low values that it is neither observable in the large-scale structure of the universe nor in the anisotropies of the cosmic microwave background radiation. Existing limits and possible future measurements, for example in KATRIN, of the absolute neutrino mass scale will provide unambiguous information on the cosmic neutrino mass density, essentially free of the uncertainty of the neutrino chemical potentials.

A precision calculation of the effective number of cosmological neutrinos

Abstract The neutrino energy density of the Universe can be conveniently parametrized in terms of the so-called effective number of neutrinos, Nνeff. This parameter enters in several cosmological observables. In particular it is an important input in those numerical codes, like CMBFAST, which are used to study the Cosmic Microwave Background anisotropy spectrum. By studying the neutrino decoupling with Boltzmann equations, one can show that this quantity differs from the number of massless neutrino species for an additional contribution due to a partial heating of neutrinos during the e± annihilations, leading to non-thermal features in their final distributions. In this Letter we review the different results obtained in the literature and perform a new analysis which takes into account, in a fully consistent way, the QED corrections at finite temperature to the photon and e± plasma equation of state. The value found for three massless active neutrinos is Nνeff=3.0395, in perfect agreement with the recommended value used in CMBFAST, Nνeff=3.04. We also discuss the case of additional relativistic relics and massive active neutrinos.

Probing neutrino masses with cmb lensing extraction

We evaluate the ability of future cosmic microwave background (CMB) experiments to measure the power spectrum of large scale structure using quadratic estimators of the weak lensing deflection field. We calculate the sensitivity of upcoming CMB experiments such as BICEP, QUaD, BRAIN, ClOVER and Planck to the nonzero total neutrino mass

Role of dense matter in collective supernova neutrino transformations

{M}_{\ensuremath{\nu}}

Neutrino mass from Cosmology

indicated by current neutrino oscillation data. We find that these experiments greatly benefit from lensing extraction techniques, improving their one-sigma sensitivity to

Current cosmological bounds on neutrino masses and relativistic relics

{M}_{\ensuremath{\nu}}

Constraining the window on sterile neutrinos as warm dark matter

by a factor of order four. The combination of data from Planck and the SAMPAN mini-satellite project would lead to

Physics of Synchronized Neutrino Oscillations Caused by Self-Interactions

\ensuremath{\sigma}({M}_{\ensuremath{\nu}})\ensuremath{\sim}0.1