  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.
