TeV scale see-saw mechanisms of neutrino mass generation, the Majorana nature of the heavy singlet neutrinos and (beta beta)(0 nu)-decay

摘要

It is shown that the Majorana nature of the heavy \udneutrinos $N_j$ having masses in the range \udof $M_j \sim (100 - 1000)$ GeV and present \udin the TeV scale type I\udand inverse see-saw scenarios of \udneutrino mass generation, is unlikely to be observable \udin the currently operating and \udfuture planned accelerator experiments (including LHC)\uddue to the existence of very strong constraints \udon the parameters and couplings responsible for the \udcorresponding $|\Delta L| = 2$ processes, \ud$L$ being the total lepton charge.\udIf the heavy Majorana neutrinos $N_j$\udare observed and they are associated only \udwith the type I\udor inverse see-saw mechanisms \udand no additional TeV scale ``new physics'', \udthey will behave\udlike Dirac fermions to a relatively \udhigh level of precision, \udbeing actually pseudo-Dirac particles.\udThe observation of effects proving \udthe Majorana nature of $N_j$ would imply that \udthese heavy neutrinos\udhave additional relatively strong \udcouplings to the \udStandard Model particles \ud(as, e.g. in the type III see-saw scenario), \udor that light neutrino masses compatible with the \udobservations are generated \udby a mechanism other than see-saw \ud(e.g., radiatively at one or two loop level) \udin which the heavy Majorana \udneutrinos $N_j$ are nevertheless involved.