Larmor radiation as a witness to the Unruh effect

TL;DR

The paper addresses whether classical Larmor radiation seen in inertial frames can be interpreted as evidence of the Unruh effect. It develops an approach based on Unruh modes and their relation to Rindler quantization to show that, for sources contained in a Rindler wedge, the inertial-frame emission probability equals the accelerated-frame absorption/emission probability into the Unruh bath, i.e. $P_{em}^{(M)} = P_{int}^{(R)}$, at leading order in perturbation theory and using Planckian statistics with $T_U = a/(2\pi)$ and $E = h\nu$. The authors extend the result from a massless scalar field to electromagnetic and gravitational fields, verifying that the same Unruh-mode framework yields the corresponding equalities and confirming universality across spins. This provides a unified, physically transparent link between classical radiation and acceleration-induced thermality, reinforcing the view that classical inertial radiation is a witness to the Unruh effect when interpreted through the accelerated frame with Planckian quanta.

Abstract

We discuss the emission of radiation from general sources in quantum scalar, electromagnetic and gravitational fields using the Rindler coordinate frame, which is suitable for a uniformly accelerated observer, in the Minkowski vacuum. In particular, we point out that, to recover the usual Larmor radiation in the interaction picture, it is necessary to incorporate the Unruh effect. Thus, the observation of classical Larmor radiation could be seen as vindicating the Unruh effect in the sense that it is not correctly reproduced in this context unless the Unruh effect is taken into account.