Exotic quantum phase transitions in systems with quenched disorder

The possibility of a quantum phase transition in a d-dimensional model with quenched disorder is analyzed via a renormalization group treatment without using the dimensionality epsilon(tau) of the imaginary time direction tau as an additional small expansion parameter. We work at the fixed physical value epsilon(tau) = 1 from the beginning, assuming the infinite correlation length in the timelike direction at temperature T = 0 as generated by an appropriate limit of a time-dependent random potential with long-range correlation in time. A stable fixed point is found to occur for realistic dimensionalities which, in the time-totally-correlated limit, is assumed to govern an exotic second order quantum phase transition in the original physical model. Also in the present approach a double expansion procedure is used but, more physically, we involve the extension of the random correlation in the tau direction rather than the artificial and doubtful expansion in small epsilon(tau).