Reexamining nonstandard interaction effects on supernova neutrino flavor oscillations

Several extensions of the standard electroweak model allow new four-fermion interactions (nu) over bar (alpha)nu(beta)(f) over barf with a strength epsilon(alphabeta)G(F), where (alpha,beta) are flavor indices. We reexamine their effects on flavor oscillations of massive (anti)neutrinos in supernovae, in order to achieve, in the region above the protoneutron star, an analytical treatment valid for generic values of the neutrino mixing angles (omega,phi,psi)=(theta(12),theta(13),theta(23)). Assuming that epsilon(alphabeta)<<1, we find that the leading effects on the flavor transitions occurring at high (H) and low (L) density along the supernova matter profile can be simply embedded through the replacements phi-->phi+epsilon(H) and omega-->omega+epsilon(L), respectively, where epsilon(H) and epsilon(L) are specific linear combinations of the epsilon(alphabeta)'s. Similar replacements hold for eventual oscillations in the Earth matter. From a phenomenological point of view, the most relevant consequence is a possible uncontrolled bias (phi-->phi+epsilon(H)) in the value of the mixing angle phi inferred by inversion of supernova neutrino data. Such a drawback, however, does not preclude the discrimination of the neutrino mass spectrum hierarchy (direct or inverse) through supernova neutrino oscillations.