Erlangen 2026 – scientific programme

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MP: Fachverband Theoretische und Mathematische Grundlagen der Physik

MP 10: Strong Fields

MP 10.5: Talk

Thursday, March 19, 2026, 14:45–15:00, KH 02.013

Essential Nonlocality of Spin and Polarization Distributions in Strong-Field Quantum Electrodynamics — Samuele Montefiori¹, Antonino Di Piazza^2,3,1, Tobias Podszus¹, Christoph H. Keitel¹, and •Matteo Tamburini¹ — ¹Max-Planck-Institut für Kernphysik, Heidelberg, Germany — ²University of Rochester, Rochester, USA — ³Laboratory for Laser Energetics, Rochester, USA

Lepton spin and photon polarization are fundamental quantum degrees of freedom that govern scattering amplitudes and observable asymmetries. Advances in high-power lasers have opened the strong-field quantum electrodynamics (QED) regime, where modeling of nonlinear Compton scattering (NCS) typically relies on the collinear, locally constant field approximation (LCFA). We show that constructing angle- and polarization-resolved NCS distributions from local, instantaneous lepton states in a uniform constant crossed field can yield unphysical spin and polarization vectors with magnitudes exceeding unity, while accounting for the full photon formation length eliminates these pathologies. We introduce a new LCFA method that integrates over the entire formation region and, when applied to electron-laser interactions and to emission in strong magnetic fields, predicts qualitative and quantitative polarization differences relative to the commonly used local, collinear-emission model.

Keywords: strong fields