Bosons After Symmetry Breaking in Quantum Field Theory

The authors present a unified description of the spontaneous symmetry breaking and its associated bosons in fermion field theory. There is no Goldstone boson in the fermion field theory models of Nambu-Jona-Lasinio, Thirring and QCD2 after the chiral symmetry is spontaneously broken in the new vacuum. The defect of the Goldstone theorem is clarified, and the "massless boson" predicted by the theorem is virtual and corresponds to just a free massless fermion and antifermion pair. Further, the authors discuss the exact spectrum of the Thirring model by the Bethe ansatz solutions, and the analytical expressions of all the physical observables enable the authors to understand the essence of the spontaneous symmetry breaking in depth. Also, the authors examine the boson spectrum in QCD2, and show that bosons always have a finite mass for SU(Nc) colours. The problem of the light cone prescription in QCD2 is discussed, and it is shown that the trivial light cone vacuum is responsible for the wrong prediction of the boson mass.