Anomalous stimulated Brillouin scattering via ultraslow light.

We study stimulated Brillouin scattering (SBS) in an ultradispersive coherent medium, and show that the properties of SBS change drastically when the group velocity of light in the material approaches or becomes less than the speed of sound. In particular, forward SBS not allowed in a dispersionless bulk medium takes place in the coherent medium.