Hydrogen energy-level shifts induced by the atom motion: Crossover from the Lamb shifts to the motion-induced shifts

When the hydrogen atom moves, the proton current generates a magnetic field which interacts with the hydrogen electron. A simple analysis shows that for the hydrogen velocity [Formula: see text] the dominant interaction between the hydrogen momentum and the electron is of order of [Formula: see text], where [Formula: see text] is the fine structure constant, v is the atom velocity, c is the speed of light and m is the electron mass. Using the Bethe–Salpeter equation, the two velocity-dependent operators of this order are derived. As is well known, the degeneracy of the energy levels with the same principal quantum number, n, and the same quantum number of the total angular momentum, j, but the different orbital angular momenta [Formula: see text] is removed by the radiative corrections (the Lamb shift) that are proportional to [Formula: see text]. It is shown that the velocity-dependent perturbation interactions remove this degeneracy as well. There is, however, an important difference between the Lamb shifts and the energy-level shifts induced by the atom motion. The Lamb shift is the diagonal correction to the energy separately for each of the degenerate states. The velocity-dependent perturbation interactions result in the off-diagonal energy corrections between the mutually degenerate states. The joint effect of these two perturbations, which are essentially different in their origin, is analyzed. Given their order of magnitude, the crossover from the Lamb shifts to the motion-induced shifts should occur at the atom velocity [Formula: see text], where [Formula: see text] is a numerical factor dependent on n and j. An experiment using the orbital motion of the Earth is proposed to test the developed theory.