Higher order corrections to the hydrogen spectrum from the standard-model extension

We have studied the effects of the standard-model extension (SME) on hydrogen as a realization of new physics effects that incorporate Lorentz and CPT violation. Specifically, we calculated the SME-induced energy level shifts at order alpha(2) times the SME parameters. We obtained contributions at this order both from the nonrelativistic effective Hamiltonian for motion of a spin-1/2 particle in the presence of SME interactions and also from SME corrections to the propagator for exchange photons. We applied our result to the 2S - 1S transition in hydrogen, which has been measured with extremely high precision. The results obtained in this work give the leading SME corrections for this transition. DOI: 10.1103/PhysRevD.86.116005