KEK Theory seminar（Dr. Ryosuke Sato）
The axion(-like particle) is ubiquitous in physics beyond the standard model. The axion has cosine-like potential, and the axion filed goes over a large number of wiggles if its initial velocity is large enough to overcome the barrier. During this process, the axion quantum fluctuation grows exponentially and this growth of quantum fluctuation gives friction to zeromode. We denote this phenomenon as axion fragmentation, and discuss it in detail. We also discuss its implication for the relaxion scenario which is a solution for the electroweak hierarchy problem.