The contribution of light Majorana neutrinos to neutrinoless double beta decay and cosmology
Stefano Dell'Oro, Simone Marcocci, Matteo Viel, Francesco Vissani
TL;DR
The paper links cosmological constraints on the sum of neutrino masses $\Sigma$ to the Majorana effective mass $m_{\beta\beta}$ governing neutrinoless double beta decay, showing that current cosmology favors the normal hierarchy and imposes tight bounds on $m_{\beta\beta}$. By translating $\Sigma$ limits into $m_{\beta\beta}$–$\text{mass, hierarchy}$ contours, it finds that the inverted hierarchy is strongly disfavored at 1σ and that next-generation tonne-scale experiments may struggle to detect a signal from light Majorana exchange under these cosmological constraints. The work emphasizes that a future $0\nu\beta\beta$ signal would likely require new physics beyond the standard light-neutrino mechanism. It also discusses potential systematic uncertainties and the value of complementary cosmological analyses in solidifying the neutrino mass picture.
Abstract
Cosmology is making impressive progress and it is producing stringent bounds on the sum of the neutrino masses Σ, a parameter of great importance for the current laboratory experiments. In this letter, we exploit the potential relevance of the analysis of Palanque-Delabrouille et al. [JCAP 1502, 045 (2015)] to the neutrinoless double beta decay (0νββ) search. This analysis indicates small values for the lightest neutrino mass, since the authors find Σ < 84 meV at 1σ C. L., and provides a 1σ preference for the normal hierarchy. The allowed values for the Majorana effective mass, probed by 0νββ, turn out to be < 75meV at 3σC.L. and lower down to less than 20meV at 1σC.L.. If this indication is confirmed, the impact on the 0νββ experiments will be tremendous since the possibility of detecting a signal will be out of the reach of the next generation of experiments.