  A doped graphene layer in the integer quantum Hall regime reveals a highly
unusual particle-hole excitation spectrum, which is calculated from the
dynamical polarizability in the random phase approximation. We find that the
elementary neutral excitations in graphene in a magnetic field are unlike those
of a standard two-dimensional electron gas (2DEG): in addition to the
upper-hybrid mode, the particle-hole spectrum is reorganized in linear
magneto-plasmons that disperse roughly parallel to $\omega=v_F q$, instead of
the usual horizontal (almost dispersionless) magneto-excitons. These modes
could be detected in an inelastic light scattering experiment.
