Vv. Sokolov et V. Zelevinsky, SIMPLE MODE ON A HIGHLY EXCITED BACKGROUND - COLLECTIVE STRENGTH AND DAMPING IN THE CONTINUUM, Physical review. C. Nuclear physics, 56(1), 1997, pp. 311-323
Simple states, such as isobaric analog states or giant resonances, emb
edded into continuum are typical for mesoscopic many-body quantum syst
ems. Due to the coupling to compound states in the same energy range,
a simple mode acquires a damping width (''internal'' dynamics). When s
tudied experimentally with the aid of various reactions, such states r
eveal enhanced cross sections in specific channels at corresponding re
sonance energies (''external'' dynamics which include direct decay of
a simple mode and decays of intrinsic compound states through their ow
n channels). We consider the interplay between internal and external d
ynamics using a general formalism of the effective non-Hermitian Hamil
tonian and looking at the situation both from the ''inside'' (strength
functions and spreading widths) and from the ''outside'' (S matrix, c
ross sections, and delay times). The restoration of isospin purity and
the disappearance of the collective strength of giant resonances at h
igh excitation energy are discussed as important particular manifestat
ions of this complex interplay.