  We study "multitrace" deformations of large N master fields in models with a
mass gap. In particular, we determine the conditions for the multitrace
couplings to drive tachyonic instabilities. These tachyons represent new local
instabilities of the associated nonlocal string theories. In the particular
case of Dp-branes at finite temperature, we consider topology-changing phase
transitions and the effect of multitrace perturbations on the corresponding
phase diagrams.
