Oscillation dynamics of active-unsterile neutrino mixing in a2+1˜mixing scheme

Abstract

We consider the possibility that sterile neutrinos exist and admit a description as unparticles; we call these {\em unsterile} neutrinos. We then examine the nature of neutrino oscillations in a model where an unsterile can mix with two active flavors with a very simple mass matrix of the see-saw type. Despite these simplifications, we find a number of remarkable features, all of which will occur generically when more realistic cases are considered. These include momentum dependent mixing angles, "invisible" decay widths for the unsterile-like mode, as well as the inheritance of a non-vanishing spectral density for the massive active-like modes. We also obtain the disappearance and appearance probabilities for the active-like neutrinos and find remarkable interference effects between the active and unsterile neutrinos as a consequence of threshold effects, yielding new oscillatory contributions with different oscillation lengths. These effects are only measurable on short baseline experiments because there both probabilities are suppressed as compared to mixing with a canonical sterile neutrino, thereby providing a diagnostics tool to discriminate unsterile from canonical sterile neutrinos. We conclude with a discussion of whether these new phenomena could aid in the reconciliation of the LSND and MiniBooNE results.