In a generic dynamical system chaos and regular motion coexist side by side,
in different parts of the phase space. The border between these, where
trajectories are neither unstable nor stable but of marginal stability,
manifests itself through intermittency, dynamics where long periods of nearly
regular motions are interrupted by irregular chaotic bursts. We discuss the
Perron-Frobenius operator formalism for such systems, and show by means of a
1-dimensional intermittent map that intermittency induces branch cuts in
dynamical zeta functions. Marginality leads to long-time dynamical
correlations, in contrast to the exponentially fast decorrelations of purely
chaotic dynamics. We apply the periodic orbit theory to quantitative
characterization of the associated power-law decays.Comment: 22 pages, 5 figure