Quantum Griffths effects in metallic systems

We show that two apparently contradictory theories on the existence of Griffiths-McCoy singularities in magnetic metallic systems ( see Castro Neto A. H. and Jones B. A., Phys. Rev. B, 62 ( 2000) 14975 and Millis A. J., Morr D. and Schmalian J., Phys. Rev. B, 66 ( 2002) 174433) are in fact mathematically equivalent. We discuss the generic phase diagram of the problem and show that there is a non-universal crossover temperature range T* < T < omega(0) where power law behavior (Griffiths-McCoy behavior) is expected. For T < T* power law behavior ceases to exist due to the destruction of quantum effects generated by the dissipation in the metallic environment. We show that T* is an analogue of the Kondo temperature and is controlled by non-universal couplings.