Symmetries as well as other special conditions can cause anomalous slowing
down of fidelity decay. These situations will be characterized, and a family of
random matrix models to emulate them generically presented. An analytic
solution based on exponentiated linear response will be given. For one
representative case the exact solution is obtained from a supersymmetric
calculation. The results agree well with dynamical calculations for a kicked
top.Comment: 4 pages, 2 figure