Speaker
Description
The QCD axion elegantly solves the longstanding strong CP problem and is well motivated dark matter candidate. To reproduce the observed dark matter abundance with axions, the decay constant f_a is considered to be around 10^12 GeV for the misalignment mechanism. On one hand, the late-time entropy production is known to allow larger f_a. On the other hand, the decay of the axion domain walls and strings can generate axion dark matter with f_a around 10^11 GeV. We propose a new mechanism for QCD axion dark matter with f_a as low as 10^8 GeV, where the axion abundance is produced from parametric resonance of the oscillating Peccei-Quinn symmetry breaking field. Several experimental efforts are currently devoted to axion searches in this range of f_a. Other potential signatures include dark radiation and warmness of dark matter. We realize this framework within various particle physics models, demonstrating complete and viable cosmologies.
