Quantum extremism: effective potential and extremal paths E. N. Argyres, M. T. M. van Kessel and R. H. P. Kleiss Eur. Phys. J. C, 65 1-2 (2010) 303-310 Published online: 04 November 2009 DOI: 10.1140/epjc/s10052-009-1179-8