Interplay between neutrino magnetic moments and $CP$ violating phases in left-right models

Abstract

We revisit the neutrino magnetic moments (MMs) in the left-right model with non-manifest symmetry. After deriving an expression in terms of the Dirac and Majorana phases, we analyze the sensitivity of neutrino MMs to these $CP$-violating phases in two scenarios: 1) a maximal right mixing in which left- and right-handed neutrinos are mixed by the same matrix; and 2) a right-handed neutrino mixing whose off-diagonal entries are much smaller than the elements in the diagonal, but where the $CP$ phases remain general. Our results show that, even though certain values of the Majorana phases can eliminate neutrino MMs, the presence of a maximal $CP$-violating phase in neutrino mixing matrix, as favored by the discrepancy between T2K results and reactor measurements in neutrino oscillations, requires that at least one neutrino have a large nonzero MM.