Hi, I recently attended several lectures on the topic of neutrino astrophysics. I wanted to verify some of the fact that I gleaned for them, specifically about the Dirac vs Majorana nature of neutrinos. 1) The most basic fact first. If a neutrino is Dirac in nature, then it has 3 flavors, and 2 spin states (helicity states), for a total of 6 possible internal states. In addition, the anti-neutrino has 6 possible internal states. In total, there are 12 possible states. If a neutrino is Majorana in nature then anti-neutrinos are simply the right handed helicity states and regular neutrinos are the left handed helicity states, and so there are only 6 total possible states instead of 12. Is this true? 2) If fact 1 is true, then this is the "deduced fact" that I have gleaned from the talks. Given that the statistical weights attributed to neutrinos are 6 and not 12 (in, for example, neutrino decoupling calculations), is it therefore true then that either neutrinos are Majorana in nature, or, if they are Dirac in nature, then the right handed Dirac states are sterile states (6 sterile states)? This would be due to the left handed nature of the weak interactions? 3) If both fact 1 and 2 are true, then I have a follow up question. If neutrinos are Dirac in nature, what does it mean, since they are massive, for the right handed states to be sterile? Since right handedness and left handedness, helicity, is only a Lorentz invariant for massless particles (Weyl fermions), then there are some particles (Lorentz frames) which will "see" a right handed neutrino as a left handed one. In that case, what does it mean for the right handed neutrino to be sterile? 4) An additional follow up question. If neutrinos are Majorana in nature, then the anti-neutrinos are right handed helicity states. In that case, if the right handed Dirac neutrinos are sterile, then why are not the Majorana anti-neutrinos sterile since they are right handed? Thanks.