Testing the Einstein equivalence principle: Atomic clocks and local Lorentz invariance

Three recent, remarkably sharp experimental tests of local Lorentz invariance are founded on an analysis of the electrostatic structure of atoms and nuclei moving through a nonmetric gravitational field. In this paper we extend this analysis to account for hyperfine and other relativistic aspects of atomic structure. One product of this work is a new quantitative interpretation of experimental tests of local Lorentz invariance that employ hydrogen-maser clocks, clocks whose ticking rates are governed by an atomic hyperfine transition. The analytical methods developed in this paper constitute a fairly complete set of tools for studying the breakdown of local Lorentz invariance in Lagrangian-based nonmetric theories of gravitation.