Speaker
Description
Up to the scale of the spontaneous breaking of Peccei-Quinn symmetry, the axion mass M_a is determined by the QCD topological susceptibility χ(T) at all temperatures T. Using an approach tying the U_A(1) and chiral symmetry breaking, we calculate χ(T) for an effective Dyson-Schwinger model of nonperturbative QCD and obtain a good agreement with lattice results for χ(T), and thus also for M_a(T), for T as high as twice the chiral restoration temperature. The axion mass follows the dictate of the QCD topological susceptibility from vanishing T over the chiral phase transition to hight T where the chiral and U_A(1) symmetries are restored. Our prediction is additionally supported by the fact that our topological susceptibility yields the T-dependence of the U_A(1) anomaly-influenced masses of η' and η mesons which is consistent with experimental evidence.
