Lorentz invariance of tachyon theories

The Lorentz invariance of tachyon theories is investigated. It is found that in the theory of spinless fermion tachyons proposed some time ago, the rates of various physical processes involving tachyons and ordinary particles are properly Lorentz covariant, in the passive sense that the measurements of the same situation by different observers are related by Lorentz transformations. This invariance requires the rates for processes involving various tachyon configurations that can be Lorentz transformed into each other to be added together. Lorentz invariance is not satisfied by spinless boson tachyon theories. The reason for the differences between tachyon theories, and between tachyon theories and ordinary theories is discussed