The meV frontier of neutrinoless double beta decay in the JUNO era

Abstract

Observing neutrinoless double beta decay would establish lepton number violation and the Majorana nature of neutrinos. Within the standard 3-flavour paradigm, the rate of this process is controlled by the effective Majorana mass $|\langle m \rangle|$, which may be severely suppressed if the neutrino mass spectrum presents normal ordering. Taking into account the first JUNO results, which significantly reduce the uncertainties on solar neutrino oscillation parameters, we provide updated conditions under which $|\langle m \rangle|_\text{NO}$ is guaranteed to exceed the $10^{-3}$ eV ($5\times 10^{-3}$ eV) threshold. We analyse both the generic case, as well as scenarios where the two Majorana phases either take CP conserving values, or at least one of them takes a CP-violating value, that are in line with predictive schemes combining flavour and generalised CP symmetries.