Twisted CFT and bilayer quantum Hall systems in the presence of an impurity

We identify the impurity interactions of the recently proposed CFT description of a bilayer quantum Hall system at filling nu = m/pm+2 [Mod. Phys. Lett. A 15 (2000) 1679]. Such a CFT is obtained by m-reduction on the one layer system, with a resulting pairing symmetry and presence of quasi-holes. For the m = 2 case boundary terms are shown to describe an impurity interaction which allows for a localized tunnel of the Kondo problem type. The presence of an anomalous fixed point is evidenced at finite coupling which is unstable with respect to unbalance and flows to a vacuum state with no quasi-holes. (C) 2003 Published by Elsevier B.V.