Constraining the absolute neutrino mass scale and Majorana CP violating phases by future 0νββ decay experiments

Assuming that neutrinos are Majorana particles, in a three-generation framework, current and future neutrino oscillation experiments can determine six out of the nine parameters which fully describe the structure of the neutrino mass matrix. We try to clarify the interplay among the remaining parameters, the absolute neutrino mass scale and two CP violating Majorana phases, and how they can be accessed by future neutrinoless double beta (0νββ) decay experiments, for the normal as well as for the inverted order of the neutrino mass spectrum. Assuming the oscillation parameters to be in the range presently allowed by atmospheric, solar, reactor, and accelerator neutrino experiments, we quantitatively estimate the bounds on m0, the lightest neutrino mass, that can be inferred if the next generation 0νββ decay experiments can probe the effective Majorana mass (mee) down to ∼1 meV. In this context we conclude that in the case that neutrinos are Majorana particles, (a) if m0 > or approx. 300 meV, i.e., within the range directly attainable by future laboratory experiments as well as astrophysical observations, then mee > or approx. 30 meV must be observed, (b) if m0<300 meV, results from future 0νββ decay experiments combined with stringent bounds on the neutrino oscillation parameters, especially the solar ones, will place much stronger limits on the allowed values of m0 than these direct experiments. For instance, if a positive signal is observed around mee=10 meV, we estimate 3 < or approx. m0/meV < or approx. 65 at 95% C.L.; on the other hand, if no signal is observed down to mee=10 meV, then m0 < or approx. 55 meV at 95% C.L