  If an electric charge is accelerated by a sufficiently intense
electromagnetic field, the effects of the radiation emitted by the charge on
the charge dynamics (radiation reaction) cannot be ignored. Here we show that
classical radiation-reaction effects alter qualitatively and quantitatively the
infrared behavior of the spectrum of the radiation emitted by an electron in
the presence of an intense electromagnetic plane wave (nonlinear Thomson
scattering). An analytical expression of the infrared limit of nonlinear
Thomson scattering is provided, which includes radiation-reaction effects and
is valid for an arbitrary plane wave. Apart from their own conceptual
importance and as a signature of classical radiation reaction, these results
provide the limiting expression of the corresponding and yet unknown exact
infrared behavior of strong-field QED in an intense plane wave.

Plasma Physics;High Energy Physics - Phenomenology