DOES POSITIVE FLUX PROVIDE A VALID DEFINITION OF TUNNELING TIMES

One of the possible definitions ([tau(OR]) Of the quantum transmission tunnelling time is based on the (normalized) positive flux at the bar rier edges. Two recent articles in this journal hold conflicting views on the validity of this definition and on the existence of negative v alues of [tau(OR)] in some cases [85, 115 (1993) and 89, 31 (1994)]. W e have performed independent calculations that show unambiguously that [tau(OR)] can be negative. Arguments are given against the interpreta tion of [tau(OR)] as a tunnelling time for transmitted particles.