Decay rate and low-energy near-horizon dynamics of acoustic black holes

We study the low-energy dynamics of an acoustic black hole near the sonic horizon. For the experimental test of black hole evaporation in the laboratory, the decay rate (greybody factor) of the acoustic black hole (sonic hole) can be calculated by the usual low-energy perturbation method. As a consequence, we obtain the decay rate of the sonic horizon from the absorption and the reflection coefficients. Moreover, we show that the thermal emission from the sonic horizon is only proportional to a control parameter which describes the velocity of the fluid.