Replicon modes and fixed-point marginal stability for systems with extended impurities

The fixed-point marginal stability, found for systems with extended quenche d impurities within a one-step replica symmetry breaking (RSB) renormalizat ion-group treatment, is further explored in terms of replicon eigenvalues, recently introduced as a simple way to investigate the fixed-point stabilit y properties with respect to the continuous RSB modes. We find that the mar ginal stability occurs again when these modes are taken into account, in co ntrast with the short-range correlated impurity case where the continuous R SB fluctuations drastically change the one-step RSB fixed-point stability s cenario. [S0163-1829(99)09429-1].