Topological and geometric properties of graph-manifolds

Abstract

This is an exposition of results on the existence problem of $\pi_1$-injective immersed and embedded surfaces in graph-manifolds, and also of nonpositively curved metrics on graph-manifolds, obtained by different authors. The results are represented from a unified point of view based on the notion of compatible cohomological classes and some difference equation on the graph of a graph-manifold (BKN-equation). Criteria for seven different properties of graph-manifolds at three levels are given: at the level of compatible cohomological classes; at the level of solutions to the BKN-equation; in terms of spectral properties of operator invariants of a graph-manifold.