  We use microlocal arguments to suggest that Lorentz symmetry breaking must
occur in a reasonably behaved tachyonic quantum field theory that permits
renormalizability. In view of this, we present a scalar tachyonic quantum field
model with manifestly broken Lorentz symmetry and without exponentially
growing/decaying modes. A notion of causality, in which anti-telephones are
excluded, and which is viewed as a form of chronology protection, is obeyed.
The field theory is constructed in a preferred tachyon frame in terms of
commuting creation/annihilation operators. We calculate some sample
(renormalized) operators in this preferred frame, argue that the Hadamard
condition is satisfied, and discuss the PCT and spin-statistics theorems for
this model.
