Dirac Neutrinos

More than eighty years after they were first proposed, neutrinos still  
remain an enigma. Although they are an integral part of Standard Model  
, still we know very little about them. In particular, the Dirac or  
Majorana nature of neutrinos remains a mystery. For a long time,  
theoretical particle physicists believed that neutrinos must be  
Majorana in nature and several elegant mass generation mechanisms have  
been proposed for Majorana neutrinos. In this talk, I will discuss  
many ways in which naturally small Dirac neutrino masses can be  
generated. I will also discuss the various interesting and sometimes
surprising connections between Dirac nature of neutrinos and Dark  
Matter stability, proton decay etc.