Sorry, this might be a dumb question. I was just reading a very old paper by Schrodinger where he's talking about different frequency modes mixing in an expanding universe.
Basically he says if the universe was expanding in any nonlinear fashion then positive and negative frequencies for some orthonormal mode expansion would mix.
That led me to wonder if the same would hold true for Left and Right handed Weyl spinors, ie. would they mix to create a mass term? I'm sure it's something that's been mentioned somewhere but I couldn't find anything off the bat.