Sphalerons and axion dynamics in high-temperature QCD

We consider the effects of sphaleronlike transitions in the high-temperature QCD plasma. Because of the chiral anomaly, these imply rapid chirality change, and strongly influence the dynamics of any axionic fields that may couple to the topological winding number of QCD. We derive a coupled set of equations describing the evolution of the axion field and chiral fermion density at high temperatures. The unsuppressed sphaleronlike transitions result in the damping of coherent axionic oscillations. The implications of this phenomenon for axion fields in early Universe cosmology is discussed.