Exact results for two integrable models of quantum impurity physics

We report exact results for two integrable quantum impurity models where the impurity is coupled to a mesoscopic ring supporting a persistent current induced by a magnetic flux through the ring (Aharonov-Bohm effect). The persistent current, a genuine finite-size effect, obtained exactly by a finite-size Bethe ansatz analysis, is insensitive to the presence of the quantum impurity. This protection of the PC from the quantum impurity only exploits the generic symmetry of the Bethe ansatz equations. It is therefore argued to be a universal property of a large class of integrable quantum impurity models holding independently of the details of the models. It is a further characteristic of integrable quantum impurity models, similar to the absence of backscattering at an integrable impurity.