Hard Recoils in the Neighborhood of Gauge Theory

by Francesco Serra

Thursday 5 Nov 2026, 13:30 → 14:30 Europe/Zurich

4/2-037 - TH meeting room (CERN)

I present a deformation of electromagnetism in which gauge invariance is relaxed by a single dimensionless parameter: the speed of a new longitudinal photon polarization in a preferred reference frame. The photon remains gapless, and the new polarization interacts with matter but decouples as its speed goes to zero, so that QED is smoothly recovered. Its main signature is not a small energy shift, but a rare hard recoil: charged particles can Cherenkov-emit the slow modes, transferring an order-one fraction of their momentum to the preferred frame while losing almost no energy. As a result, recoil-sensitive experiments, especially dark-matter direct-detection searches, constrain the deformation tens of orders of magnitude more strongly than precision tests or cosmic-ray energy loss. Gauge invariance appears as the limit in which the vacuum is perfectly transparent to charged matter, and the deformation supplements the Standard Model with a material reference frame that can absorb momentum from charged particles.