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I have two points where I would need clarification:

  1. Neutrinos are present in the early universe as flavor eigenstates and as such they decouple from the thermal bath, I guess. However, today, at least one mass eigenstate is non-relativistic, which destroys coherence. So, I am confused about this flavor eigenstates decoupling and then being composed of three mass eigenstates, one of them becoming non-relativistic at some point.

  2. Does gravity play a role in any of this? I mean, the interaction of gravitons with neutrinos (you can also imagine a sterile neutrino produced through the Dodelson-Widrow mechanism) would make their wave function to collapse, making them mass eigenstates?

user268009
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  • look at the timeline of early universe in the mainstream Big Bang model. http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/timlin.html . Before electroweak symmetry breaking all particles are massless, not only neutrinos. – anna v Dec 12 '23 at 20:03
  • EWSB plays no role in my confusion. I am talking about neutrinos that are produced as flavor eigenstates (coherent linear combination of mass eigenstates) that at some point loose this condition. This would mean that the neutrinos were produced as mass eigenstates in the first place (?). I am inclined to think that maybe the last scattering right before decoupling produce mass eigenstates instead of flavor eigenstates. However, I am far of being sure. – user268009 Dec 13 '23 at 11:09
  • this might be relevant https://physics.stackexchange.com/questions/160740/why-are-the-neutrino-flavour-eigenstates-and-mass-eigenstates-different – anna v Dec 13 '23 at 14:10

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