Theory of laser-plasma axion production

Aleksiejuk, Mark and Burton, David (2025) Theory of laser-plasma axion production. PhD thesis, Lancaster University.

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Abstract

In this thesis, we investigate the problem of axion production in laser-plasma systems, with the aim of motivating the use of Light-Shining-Through-a-Wall (LSTW) experiments in the search for axions and axion-like particles. We begin with the study of relativistic plasma waves, which culminates in a proposal of a formulation of a $1+1$D scalar field theory for laser wakefield accelerators (LWFA). With this formulation, we derived a condition for the dimensionless laser amplitude required to drive the maximum plasma wakefield only in terms of the wake velocity. Studying the case of classical axion production in laser-plasma scenarios, we derive a resonance condition for a given axion mass in terms of laser-plasma parameters. We then move on to studying axion creation in laser-plasma scenarios through the lens of the ponderomotive approximation. We propose a heuristic approach to ponderomotive dynamics and then analyse the laser-plasma-axion dynamics. Finally, we examine the problem of axion creation with consideration for the quantum nature of the axion. The case of a quantum axion field driven by a classical plasma wave and an external magnetic field is investigated. We calculate the expected axion flux of {$N \approx 6.74 \times 10^{18} \text{cm}^{-2} \text{s}^{-1} $ ($N_{m_{\psi} = 0 } \approx 1.7 \times 10^{20} \text{cm}^{-2} \text{s}^{-1} $ in the massless case) given the parameters are (axion-photon coupling) $g_{\psi} = 0.66 \times 10^{-19} \text{eV}$, (magnetic field) $B = 7 \times 10^{3} \text{eV}^{2}$ ($B \approx 35 \text{T}$)}, (plasma frequency) $\omega_{p} = 4.12 \times 10^{-2} \text{eV}$, (plasma wake phase velocity) {$v = 0.99995c $} and (axion mass) $m_{\psi} = 10^{-4} \text{eV}$. This is a promising result. Despite the real flux created being smaller due to multidimensional effects and beam dispersion, {it could be potentially feasible to produce a flux that is comparable to the hypothetical solar axion flux in terrestrial laboratories.} We also obtain an expression for the axion-photon transition rate given the form of a plasma wave driving the axion field at first order.