Let us consider a cosmic phase transition, in which fermions $\psi_f$ condense and the vacuum expectation value $|\langle \bar{\psi}_f \psi_f\rangle |$ of the resulting fermion-bilinear field gives masses $m_f$ to these fermions. One example of such a scenario is the QCD phase transition in which the $u,d,s$ quarks condense and the condensates $|\langle \bar{q}_i q_i\rangle |$ generate small effective quark masses, where $q_i =u,d,s$.

Let us consider a generic scenario without confinement, where the unbound fermions exist both before and after the phase transition. How does energy conservation work in such a scenario? Before the transition, is there only kinetic (thermal) energy in the fermion sector, $E_f = (3/2) T_f$, where $T_f$ is the fermion temperature and we set $k_B = c =1$? Or is there some form of vacuum energy released in the transition? After the transition, do the fermions have both masses $m_f$ and kinetic energy $E_f$ or is the kinetic energy transformed completely into the masses, $m_f = (3/2) T_f$?

What if we consider a supercooled phase transition, where the Universe is "stuck in the wrong vacuum" while further cooling down: after the eventual transition into the true vacuum, does the vacuum energy transfer only into reheating the Universe or also into generating masses?


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