Searches for sterile component with solar neutrinos and KamLAND

Abstract

Possible mixing of the active and sterile neutrinos has been considered both in the single Delta m^2 approximation and in the case of more than one Delta m^2. We perform global fit of the available solar neutrino data with free boron neutrino flux in the single Delta m^2 context. The best fit value corresponds to zero fraction of sterile component eta=0. We get the upper bounds: eta<0.26 (0.64) at 1\sigma (3 sigma). Due to degeneracy of parameters no one individual experiment restricts eta. The bound appears as an interplay of the SNO and Gallium as well as SuperKamiokande data. Future measurements of the NC/CC ratio at SNO can strengthen the bound down to eta<0.5 (3 sigma). If KamLAND confirms the LMA solution with its best fit point a combined analysis of the KamLAND and solar neutrino results will lead to eta<0.19 (0.56) at 1 sigma (3 sigma). We find that existence of sterile neutrino can explain the intermediate value of suppression of the KamLAND event rate: R_{KL}~0.75-0.90 in the case when more than one Delta m^2 is involved.