Francesco Vissani

Neutrinoless double beta decay: 2015 review

The discovery of neutrino masses through the observation of oscillations boosted the importance of neutrinoless double beta decay (). In this paper, we review the main features of this process, underlining its key role from both the experimental and theoretical point of view. In particular, we contextualize the in the panorama of lepton number violating processes, also assessing some possible particle physics mechanisms mediating the process. Since the existence is correlated with neutrino masses, we also review the state of the art of the theoretical understanding of neutrino masses. In the final part, the status of current experiments is presented and the prospects for the future hunt for are discussed. Also, experimental data coming from cosmological surveys are considered and their impact on expectations is examined.

LARGE R-PARITY VIOLATING COUPLINGS AND GRAND UNIFICATION

We consider the possibility that R-parity violating interactions of particles which do not involve the first generation have large (up to 1) coupling constants, λ. Such couplings, if they exist, could have a number of phenomenological consequences: renormalization of the b − τ mass ratio, generation of ντ mass in the MeV region, etc. In grand unified models, where B- and L-violating couplings appear simultaneously, proton decay can be forbidden in virtue of the hierarchical flavor structure of λ. However, due to Cabibbo-Kobayashi-Maskawa mixing this decay is induced already at one loop. Present experimental data give the upper bound λ ⪅ 10−8 (or |λ′λ″| ⪅ 7 × 10−16, on products of certain L- and B-violating coupling constants, in a more general context). The bound can be avoided if there is an asymmetry between the L- and B-violating couplings of the usual matter fields. In the SU(5) model the asymmetry can be related to the doublet-triplet splitting.

New expectations and uncertainties on neutrinoless double beta decay

The hypothesis that the Majorana mass of ordinary neutrinos dominates the rate of neutrinoless double beta decay is investigated. Predictions from neutrino oscillations are updated. Nuclear uncertainties are discussed, evaluating the impact of the quenching of the axial vector coupling constant in the nuclear medium, recently pointed out by Iachello et al. [Phys. Rev. C87, 014315 (2013)]. Also, the sensitivity of present and future experiments is assessed and possible implications of the knowledge on neutrino masses from cosmology are studied. The predictions from neutrino oscillations are compared with the results from cosmology and from neutrinoless double beta decay searches, emphasizing the important role of the measurement errors. The obstacles to an experimental determination of the Majorana phases are pointed out.

How Neutrino and Charged Fermion Masses Are Connected Within Minimal Supersymmetric SO(10)

Massive neutrinos are a generic prediction of SO(10), and models of unification cry for supersymmetry. Since we have a rather detailed information on neutrino and charged fermion masses, the real question is: how/whether it is possible to build a SO(10) supersymmetric model, that correctly incorporates fermion masses. We show that a simple construction is possible in the context of a minimal theory. We concentrate on the two heaviest generations, discuss the predictions of the model, and briefly comment on open questions.

Likelihood for supernova neutrino analyses

We derive the event-by-event likelihood that allows us to extract the complete information contained in the energy, time, and direction of supernova neutrinos, and specify it in the case of SN1987A data. We resolve discrepancies in the previous literature, numerically relevant already in the concrete case of SN1987A data.

Testing nonradiative neutrino decay scenarios with IceCube data

We test the hypothesis of non-radiative neutrinos decay using the latest IceCube data. Namely, we calculate the track-to-shower ratio expected in IceCube for the normal and inverted neutrino mass hierarchy taking into account the uncertainties in neutrino oscillation parameters. We show that the subset of data with energy above 60 TeV actually excludes the possibility of a neutrinos decay at the 1 sigma level of significance for both neutrino mass hierarchies.

Supersymmetric prediction for the muon transverse polarization in the K + → π 0 μ + ν μ decay

The muon transverse polarization in the

Neutrino Sources and Properties

K^+ \leftarrow \pi^0 \mu^+ \nu_\mu

The supersymmetric prediction for the muon transverse polarization in the

decay will be measured at the

K^+ \leftarrow \pi^0 \mu^+ \nu_\mu

10^{-4}