An analog fluid model for some tachyonic effects in field theory
  We consider the sound radiation from an acoustic point-like source moving along a supersonic ("space-like") trajectory in a fluid at rest. We call it an acoustic "tachyonic" source. We describe the radiation emitted by this supersonic source. After quantizing the acoustic perturbations, we present the distribution of phonons generated by this classical tachyonic source and the classical wave interference pattern. 
E. Arias, C. H. G. Bessa and N. F. Svaiter
hep-th gr-qc