Time-dependent Hartree-Fock studies of the sensitivity of dynamical fusion thresholds to the effective two-body interaction

Results are presented for time-dependent Hartree-Fock calculations of mostly head-on collisions of ${}_{}{}^{86}{}_{}{}^{}\mathrm{La}$ and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$. These studies demonstrate the sensitivity of the time-dependent Hartree-Fock dynamical fusion thresholds to the effective two-body interaction used in the calculations. The main thrust of this paper is to investigate the dynamical threshold which is the microscopic analog of the macroscopic extra-push threshold. We find that, for head-on collisions at bombarding energies above the interaction barrier, the onset of fusion is extremely sensitive to the interaction used. The thresholds calculated with different Skyrme forces differ by several hundreds of MeV or more, and are related to the effective mass of the interaction. We also show that the high-energy angular momentum window threshold has a pronounced force dependence, a feature which must be properly taken into account in comparing time-dependent Hartree-Fock window predictions with experimental data. Finally, it is shown that the fusion behavior can be sensitive both to the numerical time step used and to the precision of the calculation, a problem which may have implications regarding the validity of the time-dependent Hartree-Fock results after time scales of the order of ${10}^{\mathrm{-}20}$ s.