Neutrino phenomenology in a3+1+1framework

Abstract

Evidence continues to grow in the MiniBooNE (MB) antineutrino mode supporting a low-energy excess compatible with the MB neutrino mode and possibly also confirming the results of the LSND experiment. At least one sterile neutrino is required to explain the anomalies consistent with the observations of other experiments. At the same time, there is a strong tension between the positive signals of LSND and MB and the null results of νe and νµ disappearance experiments. We explore a scenario, first proposed in [1], where the presence of an additional heavy sterile neutrino (with mass well above an eV) can alleviate tension between LSND, MB and the null results of disappearance experiments. We compare and contrast this 3+1+1 scenario with the more standard 3+1 scenario and carry out global fits to all oscillation data including new 2011 MBν data. We find that the tension can be somewhat alleviated and that a phenomenologically viable window for the heavy neutrino, consistent with rare decays and BBN constraints, can be found if the fifth neutrino has a mass of order 0.3 − 10 GeV. We also find, however, that the 2011 MBν data exacerbates the tension with null experiments in both the 3+1 and 3+1+1 models when the lowest energy bins are included, resulting in little improvement in the global fit. We also discuss the implications of an additional neutrino for the reactor and gallium anomalies, and show that an oscillation explanation of the anomalies is disfavored by cosmological considerations, direct searches, and precision electroweak tests.2

The minimal 3 + 2 neutrino model versus oscillation anomalies

“…We will not consider in this paper the limit M 2 M 1 (3+1+1 minimal model), which corresponds to the proposal of [18], recently reconsidered in [16,19].…”

Light sterile neutrinos

“…The activity became more interesting after the discoveries of the Gallium neutrino anomaly [106,[145][146][147][148][179][180][181][182][183] and the reactor antineutrino anomaly [14,95,97,[101][102][103][104]106,107,[184][185][186][187][188]. The last updated global fits of short-baseline neutrino oscillation data have been presented in Refs.…”

Muon conversion to electron in nuclei in type-I seesaw models

“…Upper and lower bounds on the mixing can be obtained from supernova SN1987A data [73], since the known duration of the blast would be modified if the right-handed neutrinos are produced in the core and escape carrying energy away. BBN limits have also been explored for the very low mass region [72,[74][75][76].…”

“…[70] (see also Refs. [71,72,76,81]), Fig. 6a provides an approximate drawing of the regions excluded by these constraints (depicted as shaded areas), in particular nonunitarity bounds, kaon and pion peak searches, kaon decay searches by the PS191 experiment, D meson decay searches by the CHARM [67] and NuTeV [68] experiments 13 , Z decay searches by the Delphi experiment [69], and Higgs decays data from LHC.…”