The aim of the YRC Lunch Seminar is to promote the individual research done by young researchers within Isoquant and, at the same time, create a platform where young researchers can share and compare ideas on a regular basis starting from the fundamentals of every single topic.

The YRC Lunch Seminar is meant to be 20 min long +10 min questions + 20 min for sandwiches and drinks (open to everyone) and then another 40 min discussion just among young researchers.

**Speaker:** Tobias Podszus (MPIK)

**Venue: **Online via Zoom

**Title of Talk: **First-order strong-field QED processes including the damping of particle states

** Abstract:** Strong field QED considers electrodynamic processes in the presence of an electromagnetic background field. Here “strong” refers to the intensity of the background field, which is so high that the interactions of electrons and positrons with the background field have to be taken into account exactly in the calculations. This is done by implementing the background field in the quantization procedure of the fermion field. Exact solutions of the corresponding Dirac equation in the presence of an arbitrary plane wave field are the so called Volkov states. However, Volkov states, as well as free photon states, are not stable in the presence of the background plane-wave field but “decay” as electrons/positrons can emit photons and photons can transform into electron-positron pairs. By using the solutions of the corresponding Schwinger-Dyson equations within the locally constant field approximation, we compute the probabilities of nonlinear single Compton scattering and nonlinear Breit-Wheeler pair production by including the effects of the decay of electron, positron, and photon states. As a result, we find that the probabilities of these processes can be expressed as the integral over the light-cone time of the known probabilities valid for stable states per unit of light-cone time times a light-cone time-dependent exponential damping function for each interacting particle. Here the exponential damping functions describe the decay of the corresponding initial or final particle state before or after the interaction, respectively.

**Time: **

*12:30-13:00 talk+questions
13:00-13:20 short break
13:20-14:00 discussion YRC*

**Slides of the talk: **https://heibox.uni-heidelberg.de/f/c0485a9fd36b4632a74d/?dl=1