Axion excitation by intense laser fields in a plasma

Abstract

We study the excitation of axions by intense laser pulses propagating in a plasma. We assume that the pulses propagate along the direction of a static magnetic field. We examine two different configurations. One is that of a long pulse, with a duration Δt much longer than the electron plasma period, Δt ≫ 1/ωp. In this case, the axion field couples with the electron plasma waves (or plasmons) which are excited by the laser pulse, due to a modulational instability. The dispersion relation of the coupled axion-plasmon modes, the unstable regimes and the instability growth rates are established. The other configuration is that of a very short laser pulse, with a duration of the order of (or shorter than) the electron plasma period. In this case, the modulational instability is absent, but a laser wakefield can be excited. The latter consists of both electron density and axion field perturbations. The amplitude of this wakefield is described with a simple one-dimensional model. The two configurations (long and short pulse) can eventually be used to create axions in the laboratory and we suggest that laser plasma experiments could shed some light on the existence of these hypothetical dark matter particles.