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 \Omega parameter , \Omega _ { \nu } \leq 0.070 h ^ { -2 } , by using the current upper bound on mass parameters obtained by Heidelberg-Moscow group , \langle m \rangle _ { \beta \beta } < 0.35 eV ( 90 % CL ) .
If the bound is tighten to \langle m \rangle _ { \beta \beta } < 0.1 eV by future experiments , it would lead to a far severer bound \Omega _ { \nu } \raisebox { 0.853583 pt } { \em$ < $ } \hskip { -9.389409 pt } \raisebox { -5.121 % 496 pt } { \em$ \sim $ } 0.01 h ^ { -2 } .