Effective three-body interactions in nuclei

It is shown that the three-body forces in the $1f_{7\mathrm{/}2}$ shell, for which recently evidence was found on the basis of spectroscopic properties of the Ca isotopes and $N=28$ isotones, can be most naturally explained as an effective interaction due to excluded higher-lying shells, in particular the $2p_{3\mathrm{/}2}$ orbit.}