  A clear prediction of the Cold Dark Matter model is the existence of cuspy
dark matter halo density profiles on all mass scales. This is not in agreement
with the observed rotation curves of spiral galaxies, challenging on small
scales the otherwise successful CDM paradigm. In this work we employ high
resolution cosmological hydro-dynamical simulations to study the effects of
dissipative processes on the inner distribution of dark matter in Milky-Way
like objects (M~1e12 Msun). Our simulations include supernova feedback, and the
effects of the radiation pressure of massive stars before they explode as
supernovae. The increased stellar feedback results in the expansion of the dark
matter halo instead of contraction with respect to N-body simulations. Baryons
are able to erase the dark matter cuspy distribution creating a flat, cored,
dark matter density profile in the central several kpc of a massive Milky-Way
like halo. The profile is well fit by a Burkert profile, with fitting
parameters consistent with the observations. In addition, we obtain flat
rotation curves as well as extended, exponential stellar disk profiles. While
the stellar disk we obtain is still partially too thick to resemble the MW thin
disk, this pilot study shows that there is enough energy available in the
baryonic component to alter the dark matter distribution even in massive disc
galaxies, providing a possible solution to the long standing problem of cusps
vs. cores.
