CORRELATIONS IN ONE-DIMENSIONAL QUANTUM IMPURITY PROBLEMS WITH AN EXTERNAL-FIELD OR A TEMPERATURE

We discuss in more detail the theory of low energy excitations in quan tum impurity problems with an external field at vanishing temperature, giving further support to results of the previous paper. We then exte nd these results to the next order at low frequency, obtaining in part icular the exact expression, as a function of the bias, of the first t wo derivatives of the response function chi''(omega) at w omega = 0 in the double well problem of dissipative quantum mechanics. We also ext end our approach to the case of non-vanishing temperature and no exter nal field. Fendley et al. had obtained in that case an expression for the Hall conductance with a single impurity using a Landauer-Buttiker type approach. We recover their result in the framework of linear resp onse theory using renormalized form factors. We also obtain, as a func tion of the temperature, the first derivative of the response function chi''(omega) at omega = 0 in the double well problem of dissipative q uantum mechanics. (C) 1997 Elsevier Science B.V.