Neutrinos: Majorana or Dirac?

Abstract

Are neutrinos with definite masses Majorana or Dirac particles? This is one of the most fundamental problems of modern neutrino physics. The solution to this problem could be crucial for understanding the origin of small neutrino masses. We review here basic arguments in favor of the Majorana nature of massive neutrinos. The phenomenological theory of 0νββ-decay is briefly discussed and recent experimental data and sensitivity of future experiments are presented.