This question relates to the "hadron epoch" (after the initial quark-gluon plasma, but before the end of baryogenesis).
My understanding is that the phase transition that ends the quark-gluon plasma era happened when the ambient energy was around 175Mev.
This is lower than the masses of the top, bottom and charm quarks, so in my understanding the QGP was made of up, down and strange quarks only.
After the phase transition, the quarks assemble into hadrons. However the energy of 175MeV is below the mass of any hadron except the pion.
I conclude from this that nucleon-antinucleon pairs are not spontaneously popping up anymore. So, there is never a "hadron plasma", only the post-baryogenesis nucleons bathing in a pion gas.
Is that right?
Subsidiary question:
I used to have the somewhat naive notion that as the universe cooled, we would go through all the possible particles, from the heaviest to the lightest, and they would disappear from the picture as the universe's energy density crossed their mass threshold.
If that was true, heavy baryons like the Kaon, Xi, Upsilon, etc. would have once been created as a baryon-antibaryon pair.
I now think this was never the case: bottom-antibottom, charm-anticharm pairs were once generated in the QGP. But heavy baryon-antibaryon pairs never were, because the QGP phase transition temperature is already so much lower than their mass.
Is that a fair characterization?
