  We discuss the interplay of particle-particle and particle-hole spin-triplet
channels in high-T_c superconductors using a quasiparticle dispersion motivated
by angle-resolved photoemission. Within a generalized RPA, we find a well
defined antibound state of two holes, the pi resonance of Demler and Zhang, as
well as a bound state of a particle and a hole, the spin exciton. We show that
the energy of the pi resonance always exceeds 2 Delta, twice the maximum d-wave
gap, therefore the neutron resonance observed in the cuprates around energy
Delta is most likely a spin exciton. At the same time, we speculate that the pi
particle can exist at higher energies and might be observed in neutron
scattering around 100 meV.
