Testing the very-short-baseline neutrino anomalies at the solar sector

TL;DR

This paper investigates how sterile neutrinos at the eV scale could influence solar neutrino observations, analyzing experimental data to assess the mixing with electron neutrinos and implications for CP violation.

Contribution

It provides a quantitative analysis of solar neutrino data within a 4-flavor framework, highlighting the sensitivity to sterile neutrino mixing and the impact on CP phase considerations.

Findings

Current data are sensitive to the mixing element U_e4, comparable to U_e3.

Preference for non-zero U_e4 is statistically similar to that for U_e3.

In a 4-flavor scheme, CP phases cannot be removed from solar neutrino descriptions.

Abstract

Motivated by the accumulating hints of new sterile neutrino species at the eV scale, we explore the consequences of such an hypothesis on the solar sector phenomenology. After introducing the theoretical formalism needed to describe the MSW conversion of solar neutrinos in the presence of one (or more) sterile neutrino state(s) located "far" from the (nu_1,nu_2) "doublet", we perform a quantitative analysis of the available experimental results, focusing on the electron neutrino mixing. We find that the present data posses a sensitivity to the amplitude of the lepton mixing matrix element U_e4 --- encoding the admixture of the electron neutrino with a new mass eigenstate --- which is comparable to that achieved on the standard matrix element U_e3. In addition, and more importantly, our analysis evidences that, in a 4-flavor framework, the current preference for |U_e3|>0 is indistinguishable from that for |U_e4|>0, having both a similar statistical significance (which is ~ 1.3 sigma adopting the old reactor fluxes determinations, and ~ 1.8 sigma using their new estimates). We also point out that, differently from the standard 3-flavor case, in a 3+1 scheme the Dirac CP-violating phases cannot be eliminated from the description of solar neutrino conversions.