Tachyon instability and Kondo type models

In this paper we investigate the tachyon instability of open bosonic string theory applying methods of boundary conformal field theory. We consider compactifications on maximal tori of various simple Lie algebras with a specific background coupled to the string boundaries. The resulting world-sheet CFT is a free theory perturbed by a boundary term that is marginal but not truly marginal. Assuming that the theory flows to a nontrivial infrared fixed point that is similar to the one in Kondo model, we calculate the new spectrum and some of the Green's functions. We find that in some of the sectors the tachyon mass gets lifted that can be interpreted as a result of switching on appropriate Wilson lines. Various compactifications and patterns of flows are investigated.