"Self-tuning" and conformality

We consider an infinite-volume brane world setup where a codimension one-br ane is coupled to bulk gravity plus a scalar field with vanishing potential . The latter is protected by bulk supersymmetry, which is intact even if br ane supersymmetry is completely broken as the volume of the extra dimension is infinite. Within this setup we discuss a flat solution with a "self-tun ing" property, i.e. such a solution exists for a continuous range of values for the brane tension. This infinite-volume solution is free of any singul arities, and has the property that the brane cosmological constant is prote cted by bulk supersymmetry. We, however, also point out that consistency of the coupling between bulk gravity and brane matter generically appears to require that the brane world-volume theory be conformal.