CHIRAL PHASE-TRANSITION AND BARYON NUMBER CONSERVATION

In the standard R-4 embedding of the chiral O(4) model in 3+1 dimensio ns the winding number is not conserved near the chiral phase transitio n and thus no longer can be identified with the baryon number. In orde r to reestablish a conserved baryon number in effective low-energy mod els near and above the critical temperature T-c it is argued that insi sting in O(N) models on the angular nature of the chiral fields with f ixed boundary conditions restores conservation of the winding number. For N=2 in 1+1 dimensions it is illustrated that as a consequence of t he angular boundary conditions, nontrivial solutions exist that would be unstable in R-2, moving trajectories avoid crossing the origin, and the time evolution of random configurations after a quench leads to q uasistable soliton-antisoliton ensembles with the net winding number f ixed.