Classical and quantum radiation reaction

4 problems

• Which classical radiation-reaction equation is the classical limit of QED

  Partially resolved

  The classical Abraham-Lorentz-Dirac equation predicts electrons that run away or accelerate before a force arrives, so physicists use a cleaned-up version, the Landau-Lifshitz equation. The question is which equation quantum theory actually reduces to when quantum effects are switched off.

• Accuracy of locally constant field approximation in radiation-reaction simulations

  Partially resolved

  Computer codes for intense laser plasmas assume that light emission at each instant happens as if the field were constant. The question is how large the resulting errors are in the regime current experiments reach.

• Experimental test of electron dynamics in the radiation-dominated regime

  Open

  At high enough intensity an electron radiates away most of its energy within one laser cycle, which is predicted to trap electrons where the field is strongest instead of pushing them out. This prediction has not been tested.

• Experimental proof of stochastic photon emission in quantum radiation reaction

  Partially resolved

  Quantum theory says an electron loses energy in random discrete jumps when it emits gamma rays, while simpler models treat the loss as a smooth drag. Experiments have now seen quantum radiation reaction but cannot yet tell the random-jump picture from the smooth one.