Correlation of spin-orbit potential and effective mass

The correlation between the spin-orbit strength and effective mass at saturation density is demonstrated for various Skyrme energy-density functionals without tensor force. This correlation can be used to reduce the number of parameters in these functionals. The role of the spin-orbit interaction is considered together with the tensor force, which has a similar effect on the observable nuclear characteristics. The use of the relation obtained between the spin-orbit strength and the effective mass in the calculations of binding energies, spin-orbit splitting, and charge radii does not spoil the description of experimental data.