2026/07/28 by Francesco Serra
Physics and Astronomy · #hep-ph #hep-th
27 pages + Appendix
arxiv created 2026/07/28 · arxiv updated 2026/07/31
We modify the Standard Model by making the longitudinal component of the photon physical, propagating with small speed cL ≪ 1. This modification breaks gauge invariance and Lorentz symmetry, defining a preferred reference frame. No new fields or scales are introduced, and the photon mass is protected by a Galilean higher-form symmetry. The theory has a smooth cL→0 limit: the new modes decouple from standard matter and ordinary gauge theory predictions are recovered. Experimental constraints are severe. Charged particles Cherenkov-emit these slow modes, experiencing hard recoils against the preferred frame. The recoil rate decreases with cL, but the momentum transfer remains of the order of the particle's momentum. Dark matter detectors, sensitive to keV-scale nuclear recoils, imply an order-of-magnitude bound cL \lesssim 10-60, tens of orders of magnitude stronger than speed-difference bounds. At such values, cL is better understood as a recoil-rate factor rather than a physically relevant speed. The slow modes, practically fixed in space, make the reference frame a material medium capable of absorbing momentum from charged particles.