Standard radiation spectrum of relativistic electrons: beyond the synchrotron approximation

Radiation emitted by an electron in arbitrary, extreme relativistic motion, has been described for the first time in terms of a standard spectrum of nonsynchrotron type. Ultimately, such a nonsynchrotron spectrum is dependent not only on instantaneous trajectory curvature, but also upon its first two time derivatives and helicity, to provide a basic correction to the synchrotron approximation (SA). A strong deviation from SA has been predicted for above GeV electrons in oriented crystals.