  Angular momentum transfer from a rotating stellar bar has been proposed by
Weinberg & Katz (2002) as a mechanism to destroy dark-matter cusps in a few
rotation periods. The N-body simulations performed by these authors in support
of their claim employed spherical harmonics for the force computation and were,
as shown by Sellwood (2003), very sensitive to inclusion of asymmetric terms
(odd l,m). In order to disentangle possible numerical artifacts due to the
usage of spherical harmonics from genuine stellar dynamical effects, we
performed similar experiments using a tree code and find that significant cusp
destruction requires substantially more angular momentum than is realistically
available. However, we find that the simplified model (a N-body halo torqued by
a rotating bar pinned to the origin) undergoes an instability in which the cusp
moves away from the origin. In presence of this off-centring, spherical density
profiles centred on the origin display an apparent cusp-removal. We strongly
suspect that it is this effect which Weinberg & Katz observed. When suppressing
the artificial instability, cusp removal is very slow and requires much more
angular momentum to be transferred to the halo than a realistic stellar bar
possibly possesses.
