Time-delayed electromagnetic radiation reaction

TL;DR

This paper proposes a new model for electromagnetic radiation reaction based on a time delay between external forces and charge response, avoiding traditional issues and making testable predictions with ultra-intense lasers.

Contribution

It introduces a heuristic, non-local equation of motion incorporating a finite time delay, generalizing Larmor's formula and resolving problems of the LAD equation.

Findings

Derives a pathology-free equation of motion for charged particles.

Predicts observable delays in radiation reaction effects.

Connects delay times to fundamental charge properties.

Abstract

The Lorentz-Abraham-Dirac (LAD) equation has proved valuable in describing the motion of radiating electric charges but suffers from runaway, pre-acceleration and other ambiguities. The usual scheme is problematic because of locality, which leads to self-interaction with the propagating radiation (i.e. real photons). Instead, the present heuristic model relies on an infinitesimal time delay between the action of external forces and the inertial reaction by the charge. This yields a new and pathology-free equation of motion whereas the radiated energy-momentum is expressed as an infinite series that generalises Larmor's formula and leads to testable predictions using current and near future ultra-intense lasers. The time-delay hypothesis is to be put in parallel with recently observed delays of order $10^{-18}$s (attosecond) in photoemission by atoms and small molecules. Such behaviour is extended here to elementary charges which are supposed to exhibit delays given by the time taken by light to cross the charge's classical radius, which gives $\approx 10^{-23}$s for an electron.