Light Sterile Neutrinos, Lepton Number Violating Interactions and the LSND Anomaly

TL;DR

This paper explores how lepton number violating non-standard interactions combined with sterile neutrino mixing can explain the LSND anomaly, aligning experimental results with theoretical models and suggesting new physics implications.

Contribution

It introduces specific lepton number violating operators that reconcile LSND results with sterile neutrino models and discusses their theoretical origins and experimental consistency.

Findings

Two effective operators fit LSND and KARMEN data

Models preserve key SM parameters and agree with precision data

Parameter ranges accommodate global sterile neutrino fits

Abstract

We develop the consequences of introducing a purely leptonic, lepton number violating non-standard interaction (NSI) and standard model neutrino mixing with a fourth, sterile neutrino in the analysis of short-baseline, neutrino experiments. We focus on the muon decay at rest (DAR) result from the Liquid Scintillation Neutrino Experiment (LSND) and the Karlsruhe and Rutherford Medium Energy Neutrino Experiment (KARMEN). We make a comprehensive analysis of lepton number violating, NSI effective operators and find nine that affect muon decay relevant to LSND results. Two of these preserve the standard model (SM) value 3/4 for the Michel rho and delta parameters and, overall, show favorable agreement with precision data and the electron anti-neutrino signal from LSND data. We display theoretical models that lead to these two effective operators. In the model we choose to apply to DAR data, both electron anti-neutrino appearance from muon anti-neutrino oscillation and electron anti-neutrino survival after production from NSI decay of the positive muon contribute to the expected signal. This is a unique feature of our scheme. We find a range of parameters where both experiments can be accommodated consistently with recent global, sterile neutrino fits to short baseline data. We comment on implications of the models for new physics searches at colliders and comment on further implications of the lepton number violating interactions plus sterile neutrino-standard model neutrino mixing.