Abstract
We discuss lepton number violating processes in the context of long-baseline neutrino oscillations. We summarise and compare neutrino flavour oscillations in quantum mechanics and quantum field theory, both for standard oscillations and for those that violate lepton number. When the active neutrinos are Majorana in nature, the required helicity reversal gives a strong suppression by the neutrino mass over the energy, $(m_{\nu}/E_{\nu})^{2}$. Instead, the presence of non-standard lepton number violating interactions incorporating right-handed lepton currents at production or detection alleviate the mass suppression while also factorising the oscillation probability from the total rate. Such interactions arise from dimension-six operators in the low energy effective field theory of the Standard Model. We derive general and simplified expressions for the lepton number violating oscillation probabilities and use limits from MINOS and KamLAND to place bounds on the interaction strength in interplay with the unknown Majorana phases in neutrino mixing. We compare the bounds with those from neutrinoless double beta decay and other microscopic lepton number violating processes and outline the requirements for future short- and long-baseline neutrino oscillation experiments to improve on the existing bounds.
Highlights
The seminal confirmation of neutrino flavor oscillations by the Super-Kamiokande and SNO experiments in 1998 and 2001, respectively, initiated a golden era in the experimental and theoretical studies of massive neutrinos in the Standard Model (SM) [1,2]
We have investigated the effect of lepton number violating nonstandard interactions on long-baseline neutrino oscillations
If the light active neutrinos are of Majorana nature the να → νβ process become possible, either through a ðmν=EνÞ2 suppressed light neutrino helicity reversal or an lepton number violating (LNV) charged current (CC)-like interaction at production or detection
Summary
The seminal confirmation of neutrino flavor oscillations by the Super-Kamiokande and SNO experiments in 1998 and 2001, respectively, initiated a golden era in the experimental and theoretical studies of massive neutrinos in the Standard Model (SM) [1,2]. Often there is no way to determine the charge of the outgoing lepton at the far detector and to discern the incoming lepton as a neutrino or antineutrino This probe of lepton number is not a priority for most oscillation experiments because “να → νβ” is heavily suppressed if the mechanism is the standard Majorana neutrino helicity reversal [86,87,88,89]. We write down a general expression for the nonstandard oscillation probability and a simplified expression in the two-neutrino (2ν) mixing approximation, for the νμ − ντ sector We summarize our results and briefly outline the potential for future oscillation experiments with similar sensitivity to improve on these bounds
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