Hydrogen and Antihydrogen Spectroscopy for Studies of CPT and Lorentz   Symmetry
  A theoretical study of possible signals for CPT and Lorentz violation arising in hydrogen and antihydrogen spectroscopy is described. The analysis uses a CPT- and Lorentz-violating extension of quantum electrodynamics, obtained from a general Lorentz-violating extension of the minimal standard model with both CPT-even and CPT-odd terms. Certain 1S-2S transitions and hyperfine Zeeman lines exhibit effects at leading order in small CPT-violating couplings. 
Robert Bluhm, Alan Kostelecky, Neil Russell