Absorption cross section in an intense plane wave background

Abstract

We consider the absorption of probe photons by electrons in the presence of an intense, pulsed, background field. Our analysis reveals an interplay between regularisation and gauge invariance which distinguishes absorption from its crossing-symmetric processes, as well as a physical interpretation of absorption in terms of degenerate processes in the weak field limit. In the strong field limit we develop a locally constant field approximation (LCFA) for absorption which also exhibits new features. We benchmark the LCFA against exact analytical calculations and explore its regime of validity. Pulse shape effects are also investigated, as well as infra-red and collinear limits of the absorption process.

Self-absorption of synchrotron radiation in a laser-irradiated plasma

“…In the remaining two auxiliary variables, g = 1/2 + s 2 /[4(1 ± s)] and z = {s/[χ e (1 ± s)]} 2/3 , choosing the positive (negative) sign yields the cross section for absorption (stimulated emission). The cross section for absorption, obtained in this way, agrees with the result of a direct calculation from strong-field QED [16]. To the best of our knowledge, a QED cross section for stimulated emission has not previously been reported.…”

“…Conservation of momentum means that an electron in vacuum cannot absorb radiation without some associated emission of radiation. Absorption can occur, however, for an electron in a background electromagnetic field F µν (where the required emissions appear as 'absorption' of negative frequency modes from the background [16]). If the field is weak compared to the critical field of QED, E cr = m 2 /e [25,26], and if it varies sufficiently slowly such that quantum processes can be considered to be instantaneously constant, the interaction is controlled by the quantum parameters χ e = F µν p ν /(mE cr ) and χ γ = F µν k ν /(mE cr ), where p and k are the electron and photon momenta, e is the elementary charge and m is the electron mass.…”

One-loop multicollinear limits from 2-point amplitudes on self-dual backgrounds

“…it follows that if z is characterised by some amplitude a 0 , then the coefficient of a N 0 in the amplitude on background, out| S[eA + a] |in , is proportional to the sum of all vacuum amplitudes including N photons in all possible incoming/outgoing configurations, weighted with numerical factors and convoluted with the field profile [26,63,64]. As a sandwich plane…”

Pulse envelope effect on nonlinear Compton scattering in electron-laser collisions

“…Since the regularisation terms will play a crucial role, we briefly recap how they are derived (see e.g. [3,49]) and thereby show how they encode long-range interference on the order of the pulse duration. The scattering amplitude is an integral over all of spacetime, so the non-trivial integration direction along the laser pulse phase, is infinite.…”