  A dispersion relation for a commonly used hybrid model of plasma physics is
developed, which combines fully kinetic ions and a massless-electron fluid
description. Although this model and variations of it have been used to
describe plasma phenomena for about 40 years, to date there exists no general
dispersion relation to describe the linear wave physics contained in the model.
Previous efforts along these lines are extended here to retain arbitrary wave
propagation angles, temperature anisotropy effects, as well as additional terms
in the generalized Ohm's law which determines the electric field. A numerical
solver for the dispersion relation is developed, and linear wave physics is
benchmarked against solutions of a full Vlasov-Maxwell dispersion relation
solver. This work opens the door to a more accurate interpretation of existing
and future wave and turbulence simulations using this type of hybrid model.
