Speaker
Description
Predicted by the Peccei-Quinn (PQ) mechanism, that solves the Strong CP problem in QCD, axion is one of the most promising candidates of dark matter. In my talk, I will be reviewing recent developments in estimation of the abundance of axion CDM from topological defects. When the reheating temperature is higher than the PQ energy scale, the symmetry breaking of U(1)_{PQ} takes place in the early Universe and axion cosmic strings form, which is followed by the formation of axion domain-walls at the QCD phase transition. From the cosmological network of these defects, axions are copiously produced and contribute to the current energy density of CDM in the Universe. Based on field-theoretic simulations, we can follow the cosmological evolution of these defects and axions radiated therefrom. In conjunction with innovative analysis techniques we have introduced, our massive simulations allow to estimate the axion abundance more precisely than ever before. We derive a constraint on the PQ energy scale from the axion CDM abundance and discuss implications for cosmological scenarios.
