The role that neutrinos have played in the evolution of the Universe is the focus of one of the most fascinating research areas that has stemmed from the interplay between cosmology, astrophysics and ...particle physics. In this self-contained book, the authors bring together all aspects of the role of neutrinos in cosmology, spanning from leptogenesis to primordial nucleosynthesis, their role in CMB and structure formation, to the problem of their direct detection. The book starts by guiding the reader through aspects of fundamental neutrino physics, such as the standard cosmological model and the statistical mechanics in the expanding Universe, before discussing the history of neutrinos in chronological order from the very early stages until today. This timely book will interest graduate students and researchers in astrophysics, cosmology and particle physics, who work with either a theoretical or experimental focus.
We perform a study of the flavor evolution in the early universe of a multiflavor active-sterile neutrino system with parameters inspired by the short-baseline neutrino anomalies. In a ...neutrino-symmetric bath a "thermal" population of the sterile state would quickly grow, but in the presence of primordial neutrino asymmetries a self-suppression as well as a resonant sterile neutrino production can take place, depending on temperature and chosen parameters. In order to characterize these effects, we go beyond the usual average momentum and single-mixing approximations and consider a multimomentum and multiflavor treatment of the kinetic equations. We find that the enhancement obtained in this case with respect to the average momentum approximation is significant, up to ~ 20% of a degree of freedom. Such a detailed and computationally demanding treatment further raises the asymmetry values required to significantly suppress the sterile neutrino production, up to L sub(nu) > ~ O(10 super(-2)). For such asymmetries, however, the active-sterile flavor conversions happen so late that significant distortions are produced in the electron (anti)neutrino spectra. The larger L sub(nu), the more the impact of these distortions takes over as a dominant cosmological effect, notably increasing the super(4)He abundance in primordial nucleosynthesis. The standard expression of the primordial yields in terms of the effective number of neutrinos and asymmetries is also greatly altered. We numerically estimate the magnitude of such effects for a few representative cases and comment on the implications for current cosmological measurements.
Light sterile neutrinos can be excited by oscillations with active neutrinos in the early universe. Their properties can be constrained by their contribution as extra-radiation, parameterized in ...terms of the effective number of neutrino species Neff, and to the universe energy density today Ωνh2. Both these parameters have been measured to quite a good precision by the Planck satellite experiment. We use this result to update the bounds on the parameter space of (3+1) sterile neutrino scenarios, with an active-sterile neutrino mass squared splitting in the range (10−5–102) eV2. We consider both normal and inverted mass orderings for the active and sterile states. For the first time we take into account the possibility of two non-vanishing active-sterile mixing angles. We find that the bounds are more stringent than those obtained in laboratory experiments. This leads to a strong tension with the short-baseline hints of light sterile neutrinos. In order to relieve this disagreement, modifications of the standard cosmological scenario, e.g. large primordial neutrino asymmetries, are required.
The symmetry of the theory of relativity under diffeomorphisms strongly depends on the equivalence principle. Violation of Equivalence Principle (VEP) can be tested by looking for deviations from the ...standard framework of neutrino oscillations. In recent works, it has been shown that strong constraints on the VEP parameter space can be placed by means of the atmospheric neutrinos observed by the IceCube neutrino telescope. In this paper, we focus on the KM3NeT neutrino telescope and perform a forecast analysis to assess its capacity to probe VEP. Most importantly, we examine the crucial role played by systematic uncertainties affecting the neutrino observations. We find that KM3NeT will constrain VEP parameters times the local gravitational potential at the level of 10−27. Due to the systematic-dominated regime, independent analyses from different neutrino telescopes are fundamental for robustly testing the equivalence principle.
We consider the decoupling of neutrinos in the early Universe in presence of non-standard neutral current neutrino–electron interactions (NSI). We first discuss a semi-analytical approach to solve ...the relevant kinetic equations and then present the results of fully numerical and momentum-dependent calculations, including flavor neutrino oscillations. We present our results in terms of both the effective number of neutrino species (
N
eff
) and the impact on the abundance of
4He produced during big bang nucleosynthesis. We find that the presence of neutrino–electron NSI may enhance the entropy transfer from electron–positron pairs into neutrinos instead of photons, up to a value of
N
eff
≃
3.12
for NSI parameters within the ranges allowed by present laboratory data, which is almost three times the effect that appears for standard weak interactions. Thus non-standard neutrino–electron interactions do not essentially modify the density of relic neutrinos nor the bounds on neutrino properties from cosmological observables, such as their mass.
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