  In view of recent experiments on ultra-cold polarized fermions, the
zero-range potential approach is generalized to situations where two-body
scattering is resonant in the p-wave channel. We introduce a modified scalar
product which reveals a deep relation between the geometry of the Hilbert space
and the interaction. This formulation is used to obtain a simple interpretation
for the transfer rates between atomic and molecular states within a two
branches picture of the many-body system close to resonance. At resonance, the
energy of the dilute gas is found to vary linearly with density.
