INFRARED SINGULARITIES IN D-LESS-THAN-OR-EQUAL-TO-2 DISORDERED INTERACTING SYSTEMS

We address the problem of infrared singularities in the perturbation t heory for disordered interacting systems in d less than or equal to 2. We show that a typical sufficiently large interacting system exhibits a linear instability in-the spin-triplet channel. In the density-dens ity channel, although stability is preserved, a large number of soft m odes is accumulated. These phenomena are responsible for the instabili ty of the weak-interacting fixed point. Although generic, the unstable direction and soft modes are highly sample specific and cannot be eff ectively captured by conventional techniques;based on an averaging pro cedure. Rather, the instability is determined by the largest eigenvalu es of the polarization operator. We propose to employ the optimal-fluc tuation method for evaluating the probability of such events.