Discrepancies in experiments with cold hydrogen atoms

Recent experiments with atomic clocks and hydrogen gas samples have shown discrepancies between theory and experiment. There are serious disagreements with respect to four different parameters: two different frequency shift parameters and a line broadening cross section relating to the H maser, and a longitudinal relaxation rate observed in a hydrogen gas sample. We study the changes in the short-range singlet and triplet potentials that would be needed to eliminate the above discrepancies. We find that no such changes can remove all four discrepancies simultaneously. In addition, we investigate a possible role of spin-dipole interactions, which have been neglected in previous calculations.