The Wigner time delay of a classically chaotic quantum system can be
expressed semiclassically either in terms of pairs of scattering trajectories
that enter and leave the system or in terms of the periodic orbits trapped
inside the system. We show how these two pictures are related on the
semiclassical level. We start from the semiclassical formula with the
scattering trajectories and derive from it all terms in the periodic orbit
formula for the time delay. The main ingredient in this calculation is a new
type of correlation between scattering trajectories which is due to
trajectories that approach the trapped periodic orbits closely. The equivalence
between the two pictures is also demonstrated by considering correlation
functions of the time delay. A corresponding calculation for the conductance
gives no periodic orbit contributions in leading order.Comment: 21 pages, 5 figure
