  We present a characterization of a bosonic field theory driven by a free
(Gaussian) tachyonic Hamiltonian. This regime is obtained from a theory
describing two coupled bosonic fields after a regular quench. Relevant physical
quantities such as simple correlators, entanglement entropies, and the mutual
information of disconnected subregions are computed. We show that the causal
structure resembles a critical (massless) quench. For short times, physical
quantities also resemble critical quenches. However, exponential divergences
end up dominating the dynamics in a very characteristic way. This is related to
the fact that the low-frequency modes do not equilibrate. Some applications and
extensions are outlined.
