I know that normally we can ignore gravitational effects when considering interactions between subatomic particles. As I understand it the reason for this is that either they are interacting electromagnetically in which case the gravitational interaction is negligible or they are both fermions and therefore can't get too close by the Paulo exclusion principle, or they are particle anti particle pair and annihilate when they get to close. It seems however that if we were to have an election neutrino and say a tau neutrino, there would be no limit as to how close they can get, in which case they should be able to get close enough for gravity to have some obvious effects. Am I wrong about this? If not, are there experiments than can measure this?