Radiation from charged particles due to explicit symmetry breaking in a gravitational field

Abstract

The paradox of a free falling radiating charged particle in a gravitational field is a well-known fascinating conceptual challenge that involves classical electrodynamics and general relativity (GR). We discuss this paradox considering the emission of radiation as a consequence of an explicit space/time symmetry breaking involving the electric field within the trajectory of the particle seen from an external observer. This occurs in certain particular cases when the relative motion of the charged particle does not follow a geodesic of the motion dictated by the explicit Lagrangian formulation of the problem and thus from the metric of spacetime. The problem is equivalent to the breaking of symmetry within the spatial configuration of a radiating system like an antenna: when the current is not conserved at a certain instant of time within a closed region, then emission of radiation occurs [D. Sinha and G. A. J. Amaratunga, Phys. Rev. Lett. 114(7) (2015) 147701]. Radiation from a system of charges is possible only when there is explicit breaking of symmetry in the electric field in space and time.