Time of arrival in the presence of interactions
  We introduce a formalism for the calculation of the time of arrival t at a space point for particles traveling through interacting media. We develop a general formulation that employs quantum canonical transformations from the free to the interacting cases to construct t in the context of the Positive Operator Valued Measures. We then compute the probability distribution in the times of arrival at a point for particles that have undergone reflection, transmission or tunneling off finite potential barriers. For narrow Gaussian initial wave packets we obtain multimodal time distributions of the reflected packets and a combination of the Hartman effect with unexpected retardation in tunneling. We also employ explicitly our formalism to deal with arrivals in the interaction region for the step and linear potentials. 
J. Leon (1), J. Julve (1), P. Pitanga (2) and F. J. de Urries (3) ((1)   IMAFF/CSIC, Madrid, Spain, (2) UFRJ, Rio de Janeiro...