Constraining neutrino mass from neutrinoless double beta decay

We study the implications of the recent results on neutrinoless double beta decay (0v beta beta) from GERDA-I (Ge-76) and KamLAND-Zen + EXO-200 (Xe-136) and the upper limit on the sum of light neutrino masses from Planck. We show that the upper limits on the effective neutrino mass from Xe-136 are stronger than those from Ge-76 for most of the recent calculations of the nuclear matrix elements (NMEs). We also analyze the compatibility of these limits with the claimed observation in Ge-76 and show that while the updated claim value is still compatible with the recent GERDA limit as well as the individual Xe-136 limits for a few NME calculations, it is inconsistent with the combined Xe-136 limit for all but one NME. Imposing the most stringent limit from Planck, we find that the canonical light neutrino contribution cannot saturate the current limit, irrespective of the NME uncertainties. Saturation can be reached by inclusion of the right-handed (RH) neutrino contributions in TeV-scale left-right symmetric models with type-II seesaw. This imposes a lower limit on the lightest neutrino mass. Using the 0v beta beta bounds, we also derive correlated constraints in the RH sector, complimentary to those from direct searches at the LHC.