Time evolution of decay for purely absorptive potentials: The effect of   spectral singularities
  We consider an analytical approach that involves the complex poles of the propagator to investigate the effect due to the lack of time reversal invariance on the time evolution of decay for purely absorptive potentials. We find that the choice of the initial state may change the exponential decaying regime into a nonexponential oscillatory behavior at time scales of the order of a lifetime of the system. We illustrate this effect for a spectral singularity corresponding to a purely imaginary delta-shell potential. 
Gast\'on Garc\'ia-Calder\'on and Lorea Chaos-Cador
quant-ph math-ph math.MP