Double Beta Decay Constraints on Neutrino Masses and Mixing; Reanalysis with KamLAND Data

Abstract

In the light of KamLAND data just released, we reanalyze and update the constraints on neutrino masses and mixing parameters, the most general ones that can be derived in three-flavor mixing scheme of neutrinos with use of the bounds imposed by neutrinoless double beta decay search and reactor experiments. We point out that with KamLAND data and assuming Majorana neutrinos one can derive, for the first time, an upper bound on neutrino contribution to the cosmological Ωparameter, Ω_ν \leq 0.070 h^{-2}, by using the current upper bound on mass parameters obtained by Heidelberg-Moscow group, < m >_{ββ} < 0.35 eV (90 % CL). If the bound is tighten to < m >_{ββ} < 0.1 eV by future experiments, it would lead to a far severer bound Ω_ν \lsim 0.01 h^{-2}.