Speaker
Ken ́ichi Saikawa
(DESY; Hamburg)
Description
Abstract: The axion arises as a pseudo Nambu-Goldstone boson from the spontaneous breaking
of a hypothetical global Peccei-Quinn symmetry introduced to provide a solution to the strong CP
problem of quantum chromodynamics. Due to the weakness of the coupling with ordinary
matters, the axion is regarded as a viable candidate of dark matter of the universe. However, there
is a theoretical uncertainty on the determination of the relic abundance of dark matter axions,
which comes from a poor understanding of their production mechanism. In particular, the recent
analysis of the spectrum of axions radiated from networks of topological defects revealed that
axions produced by the defects give significant contributions to the relic cold dark matter
abundance if the Peccei-Quinn symmetry is broken after inflation. In this talk, I will report the
recent theoretical estimation of the axion dark matter abundance based on the results of field-
theoretic lattice simulations of topological defects and discuss its implications for future
experimental tests.
