  We perform controlled numerical experiments to asses the effect of baryon
mass loss on the inner structure of large galactic dark matter haloes. This
mass expulsion is intended to mimic both the supernovae and AGN feedbacks, as
well as the evolution of stellar populations. This study is meant in particular
for precursors of massive Early Type Galaxies, wherein strong AGN feedback
(often dubbed "QSO mode" in galaxy formation models) has been proposed to
remove on a short timescale, of the order of a few dynamical times, a
substantial fraction of their baryons. In a previous paper we evaluated the
observational consequences (size increase) of this process on the galactic
structure (Ragone-Figueroa & Granato 2011). Here we focus on the distribution
of dark matter in the galactic region. It is shown that the inner region of the
DM halo expands and its density profile flattens by a sizeable amount, with
little dependence on the expulsion timescale. We also evaluate the effect of
the commonly made approximation of treating the baryonic component as a
potential that changes in intensity without any variation in shape. This
approximation leads to some underestimates of the halo expansion and its slope
flattening. We conclude that cuspy density profiles in ETGs could be difficult
to reconcile with an effective AGN (or stellar) feedback during the evolution
of these systems.
