Correlations in one-dimensional quantum impurity problems with an external field or a temperature Original Research Article

We discuss in more detail the theory of low energy excitations in quantum impurity problems with an external field at vanishing temperature, giving further support to results of the previous paper. We then extend these results to the next order at low frequency, obtaining in particular the exact expression, as a function of the bias, of the first two derivatives of the response function χ″ (ω) at ω = 0 in the double well problem of dissipative quantum mechanics.