  Two-particle scattering in graphene is a multichannel problem, where the
energies of the identical or opposite-helicity channels lie in disjoint energy
segments. Due to the absence of Galilean invariance, these segments depend on
the total momentum $Q$. The dispersion relations for the two opposite-helicity
scattering channels are analogous to those of two one-dimensional tight-binding
lattices with opposite dispersion relations, which are known to easily bind
states at their edges. When an $s$-wave separable interaction potential is
assumed, those bound states reveal themselves as three Feshbach resonances in
the identical-helicity channel. In the limit $Q \rightarrow 0$, one of the
resonances survives and the opposite-helicity scattering amplitudes vanish.
