UL(N) × UR(N)-Invariant Four-Fermion Interactions and Nambu–Goldstone Mechanism at Finite Temperature**The project supported partially by National Natural Science Foundation of China and by Grant No. LWTZ-1298 of the Chinese Academy of Sciences

Abstract

In a chiral UL(N) × UR(N) fermion model of NJL-form, we prove that, if all the fermions are assumed to have equal masses and equal chemical potentials, then at the finite temperature T below the symmetry restoration temperature Tc, there will be N2 massive scalar composite particles and N2 massless pseudoscalar composite particles (Nambu–Goldstone bosons). This shows that the Goldstone theorem at finite temperature for spontaneous symmetry breaking UL(N) × UR(N) → UL+R(N) is valid and consistent with the real-time formalism of thermal field theory in this model.