1. The problem statement, all variables and given/known data I need to construct the Feynman loop integral for the following diagram: (*) where [itex]\nu[/itex]L is the left-handed neutrino, [itex]\phi[/itex] is a scalar particle and N is a heavy neutrino with a Majorana mass. 2. Relevant equations N/A 3. The attempt at a solution I'm trying to determine it by comparing it to the self-energy of the electron: which gives . 1) Since there's a scalar propagator ([itex]\phi[/itex]) in (*), do I need to use these Feynman rules?: where m = m[itex]\phi[/itex] in this case. (Taken from http://bolvan.ph.utexas.edu/~vadim/Classes/2011f/QED.pdf). 2) How do I deal with the fact that the neutrinos are left-handed? Do I just add factors of (1-γ5)/2 in the (-igδβα) terms? 3) For Dirac particles, the propagator is: But how does this change if the particle (in this case, N) is Majorana? Any help would be appreciated. Thanks!