Nuclear structure of lowest 229Th states and time-dependent fundamental constants

The electromagnetic transition between the almost degenerate 5/2(+) and 3/2(+) states in Th-229 is deemed to be very sensitive to potential changes in the fine structure constant alpha. State of the art Hartree-Fock and Hartree-Fock-Bogoliubov calculations are performed to compute the difference in Coulomb energies of the two states that determines the sensitivity of the transition frequency nu on variations in alpha. The kinetic energies are also calculated that reflect a possible variation in the nucleon or quark masses. As the two states differ mainly in the orbit occupied by the last unpaired neutron the Coulomb energy difference results from a change in the nuclear polarization of the proton distribution. This effect turns out to be rather small and to depend on the nuclear model. The sensitivity q(s) of the frequency shift delta nu on delta alpha/alpha(delta nu=q(s)delta alpha/alpha) varies for the different models between about +10(20) Hz and -10(20) Hz. Therefore, much more effort must be put into the improvement of the nuclear models before one can draw conclusions from a measured drift in the transition frequency on the size of a temporal drift of alpha. .