  To assess the effect of baryonic ``pinching'' of galaxy cluster dark matter
(DM) haloes, cosmological (LCDM) TreeSPH simulations of the formation and
evolution of two galaxy clusters have been performed, with and without baryons
included.
  The simulations with baryons invoke star formation, chemical evolution with
non-instantaneous recycling, metallicity dependent radiative cooling, strong
star-burst, driven galactic super-winds and the effects of a meta-galactic UV
field, including simplified radiative transfer. The two clusters have T_X~3 and
6 keV, respectively, and, at z~0, both host a prominent, central cD galaxy.
  Comparing the simulations without and with baryons, it is found for the
latter that the inner DM density profiles, r<50-100 kpc, steepen considerably:
Delta(alpha)~0.5-0.6, where -alpha is the logarithmic DM density gradient. This
is mainly due to the central stellar cDs becoming very massive, as a
consequence of the onset of late time cooling flows and related star formation.
Once these spurious cooling flows have been corrected for, and the cluster
gravitational potentials dynamically adjusted, much smaller pinching effects
are found: Delta(alpha)~0.1. Including the effects of baryonic pinching,
central slopes of alpha~1.0 and 1.2 are found for the DM in the two clusters,
interestingly close to recent observational findings.
  For the simulations with baryons, the inner density profile of DM+ICM gas
combined is found to be only very marginally steeper than that of the DM,
Delta(alpha)<0.05. However, the total matter inner density profiles are found
to be Delta(alpha)~0.5 steeper than the inner profiles in the dark matter only
simulations.
