Collapse of incoherent light beams in inertial bulk Kerr media

We use the coherent density function theory to show that partially coherent beams are unstable and may collapse in inertial bulk Kerr media. The thres hold power for collapse, and its dependence on the degree of coherence, is found analytically and checked-numerically. The internal dynamics of the wa lk-off modes is illustrated for collapsing and diffracting partially cohere nt beams.