Status of Oscillation plus Decay of Atmospheric and Long-Baseline Neutrinos

TL;DR

This study analyzes how neutrino oscillation and invisible decay affect atmospheric and long-baseline neutrino experiments, finding no strong evidence for decay and setting lower bounds on neutrino lifetime.

Contribution

It provides a comprehensive global analysis of neutrino oscillation combined with decay, offering new constraints on neutrino decay lifetime and coupling in Majoron models.

Findings

Decay scenario fits atmospheric data reasonably well

No significant evidence for neutrino decay found

Sets lower bound on neutrino decay lifetime tau_3/m_3 > 9.3e-11 s/eV

Abstract

We study the interplay of neutrino oscillation and invisible decay in atmospheric and long-baseline neutrinos experiments. We perform a global analysis of the full atmospheric data from Super-Kamiokande together with long-baseline K2K and MINOS in these scenarios. We find that the admixture of nu_mu -> nu_tau oscillations with parameters Delta_m32^2 = 2.6e-3 eV^2 and theta_23 ~ 34 degrees plus decay of the heavy neutrino, nu_3, with lifetime of the order tau_3/m_3 ~ 2.6e-12 s/eV provides a reasonable fit to atmospheric neutrinos, although this solution becomes more disfavored (dropping to the 99% CL) once long-baseline data are included. Other than this local minimum, the analysis shows no evidence in favor of a non-vanishing neutrino decay width and an lower bound on the decay lifetime tau_3/m_3 > 9.3e-11 s/eV is set at 99% CL. In the framework of Majoron models, this constraint can be translated into a bound on the Majoron coupling to nu_3 and an unmixed very light sterile state, |g_s3| < 8.6e-3 (2.2 eV/m_3).