PT-symmetric square well

Below a (comparatively large) measure of non-hermiticity Z = Z(0)((crit)) > 0 of a PT symmetrically complexified square well, bound states are constru cted non-numerically. All their energies prove real and continuous in the ( Hermitian) limit Z --> 0. Beyond the threshold Z(0)((crit)) (and, in genera l, beyond Z(m)((crit)) at m = 0, 1,...) the lowest two real energies (i.e., E-2m and E2m+l) are shown to merge and disappear. (C) 2001 Elsevier Scienc e B.V. All rights reserved.