Neutrinoless double beta decay in seesaw models

We study the general phenomenology of neutrinoless double beta decay in seesaw models. In particular, we focus on the dependence of the neutrinoless double beta decay rate on the mass of the extra states introduced to account for the Majorana masses of light neutrinos. For this purpose, we compute the nuclear matrix elements as functions of the mass of the mediating fermions and estimate the associated uncertainties. We then discuss what can be inferred on the seesaw model parameters in the different mass regimes and clarify how the contribution of the light neutrinos should always be taken into account when deriving bounds on the extra parameters. Conversely, the extra states can also have a significant impact, cancelling the Standard Model neutrino contribution for masses lighter than the nuclear scale and leading to vanishing neutrinoless double beta decay amplitudes even if neutrinos are Majorana particles. We also discuss how seesaw models could reconcile large rates of neutrinoless double beta decay with more stringent cosmological bounds on neutrino masses.Comment: 34 pages, 5 eps figures and 1 axodraw figure. Final version published in JHEP. NME results available in Appendi

Quest for electron decay e^- -> neutrino_e + gamma with liquid Xenon scintillator

A new lifetime limit on the charge nonconserving (CNC) electron decay through the channel electron into neutino+gamma has been established analyzing a 2257.7 kg day event sample collected by the about 6.5 kg liquid xenon DAMA scintillator at the Gran Sasso National Laboratory of INFN. This limit is tau>2.0(3.4) x 10^{26} yr at 90% (68%) C.L., one order of magnitude higher than the current limit for that channel

Quest for electron decay e^- -> neutrino_e + gamma with liquid Xenon scintillator

A new lifetime limit on the charge nonconserving (CNC) electron decay through the channel electron into neutino+gamma has been established analyzing a 2257.7 kg day event sample collected by the about 6.5 kg liquid xenon DAMA scintillator at the Gran Sasso National Laboratory of INFN. This limit is tau>2.0(3.4) x 10^{26} yr at 90% (68%) C.L., one order of magnitude higher than the current limit for that channel

New limits on spin-dependent coupled WIMPs and on 2 beta processes in Ca-40 and Ca-46 by using low radioactive CaF2(Eu) crystal scintillators

The development of highly radio pure CaF2(Eu) crystal scintillators has been performed aiming at a substantial sensitivity enhancement of the 2 beta decay investigation and of the search for dark matter particles with spin-dependent (SD) interaction. The results of CaF2(Eu) background measurements and simulation are presented. New and highly improved T-1/2 limits on the 2 beta decay of Ca-46 and the double electron capture of Ca-40 are obtained as well as further results on SD coupled WIMPs. (C) 1999 Elsevier Science B.V. All rights reserved