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arXiv · 1704.07779

Disparities of Larmor's/Liénard's formulations with special relativity and energy-momentum conservation

Ashok K. Singal
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Abstract

It is shown that the familiar Larmor's formula or its relativistic generalization, Liénard's formula, widely believed to represent the instantaneous radiative losses from an accelerated charge, are not compatible with the special theory of relativity (STR). We demonstrate this in the case of a charge emitting synchrotron radiation where the agency responsible for acceleration (the magnetic field) does no work and thus all the energy-momentum carried by the radiation has to be balanced unambiguously against the kinetic energy-momentum of the moving charge. The application of the radiation reaction inferred from Larmor's/Liénard's formulas in two different inertial frames, yields results that are not in conformity with the relativistic transformations. Further, we show that energy-momentum conservation is violated in all inertial frames when we try to balance the energy-momentum carried by the electromagnetic radiation against the loss of kinetic energy and momentum of the radiating charge in accordance with Larmor's formula. We point out a mathematical subtlety in the applicability of Poynting's theorem, that seems to have been overlooked in the text-book derivation of Larmor's formula, where a proper distinction between "real" and "retarded" times was not kept, and which has therefore given rise to such anomalies, including the mysterious Schott term, which happens to be nothing but the difference in rate of change of energy in self-fields of the charge between retarded and present times.

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Ashok K. Singal. 2018-02-21. Disparities of Larmor's/Liénard's formulations with special relativity and energy-momentum conservation. https://doi.org/10.1088/2399-6528%2Faab2c3

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