The Bose-Fermi Kondo model and heavy-fermion quantum criticality

Bose-Fermi Kondo models (BFKMs), describing a local magnetic moment coupled to a conduction band and a dissipative bosonic bath, are of current interest in connection with non-Fermi-liquid behavior of quantum critical heavy-fermions [1]. The latter are believed to be well-described by the Kondo lattice model, which maps onto a self-consistent BFKM within the extended dynamical mean-field theory (EDMFT) framework [2]. With a view to providing conclusive solutions of the KLM we have extended the numerical renormalization group (NRG) approach to tackle Bose-Fermi quantum impurity problems [3]. Here we treat the BFKM with Ising-symmetry couplings to a bosonic bath described by spectral function $\eta(\omega)\propto\omega^s$. The method gives an excellent account of the critical properties of the model, which we show belongs to the same universality class as the spin boson model. For sub-Ohmic bath exponents $0