| The origin of the neutrino masses calls for new physics beyond the standard model.It is natural to connect new physics with the Majorana nature of the neutrinos.The Majorana neutrino masses can be generated in seesaw mechanisms and radiative neutrino mass generation mechanisms.And the Majorana nature of the neutrinos can be probed by neutrinoless double beta decay(0νββ).In this paper we discuss the correlation between neutrino mass and 0νββ.We give a brief introduction about the standard interpretation of 0νββ.In this model,0νββprocess is determined by the effective Majorana masss of electron neutrino,so it can be seen in the running and planning experiments only if the effective masss parameter is big enough.In many cases,new physics contributions to 0νββ cannot be neglected.We review 0νββin left-right symmetric model with Type I+II seesaw and analyze every contribution to 0νββ in this model.Then we show that in left-right symmetric model with Type-II seesaw dominance,the dominant contribution to 0νββ could come from left-handed current with light neutrino exchange or right-handed current with heavy neutrino exchange.An enhanced 0νββ process can also originate from a tiny effective neutrino masss.In this paper we introduce some extended two Higgs doublet models.We realize these models by introducing two scalar singlets among which one carries a singly electric charge while the other one carries a doubly electric charge.We can obtain a dominant Majorana neutrino mass matrix at two-loop level.And the structure of the neutrino mass matrix can be fully determined by the symmetric Yukawa couplings of the doubly charged scalar to the right-handed leptons.Meanwhile,The one-loop 0νββ process can arrive at an observable level even if the electron neutrino mass is extremely small.We also study other experimental constraints and implications including some rare processes and Higgs phenomenology. |
