  We analyze a mean-field model of electrons on a square lattice with two types
of interaction: forward scattering favoring a d-wave Pomeranchuk instability
and a BCS pairing interaction driving d-wave superconductivity. Tuning the
interaction parameters a rich variety of phase diagrams is obtained. If the BCS
interaction is not too strong, Fermi surface symmetry breaking is stabilized
around van Hove filling, and coexists with superconductivity at low
temperatures. For pure forward scattering Fermi surface symmetry breaking
occurs typically via a first order transition at low temperatures. The presence
of superconductivity reduces the first order character of this transition and,
if strong enough, can turn it into a continuous one. This gives rise to a
quantum critical point within the superconducting phase. The superconducting
gap tends to suppress Fermi surface symmetry breaking. For a relatively strong
BCS interaction, Fermi surface symmetry breaking can be limited to intermediate
temperatures, or can be suppressed completely by pairing.
