Constraining the absolute neutrino mass scale and Majorana CP violating phases by future neutrinoless double beta decay experiments

Abstract

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 $m_0$, the lightest neutrino mass, that can be infered if the next generation $0νββ$ decay experiments can probe the effective Majorana mass ($m_{ee}$) down to $\sim$ 1 meV. In this context we conclude that in the case neutrinos are Majorana particles: (a) if $m_0 \gsim 300$ meV, {\em i.e.}, within the range directly attainable by future laboratory experiments as well as astrophysical observations, then $m_{ee} \gsim 30$ meV must be observed; (b) if $m_0 < 300$ meV, results from future $0νββ$ decay experiments combined with stringent bounds on the neutrino oscillation parameters, specially the solar ones, will place much stronger limits on the allowed values of $m_0$ than these direct experiments.