Let M be a manifold (with
boundary) of dimension ≥ 3, such that its interior admits a hyperbolic metric of
finite volume. We discuss the possible limits arising from sequences of relative
fundamental cycles approximating the simplicial volume ∥M,∂M∥, using
ergodic theory of unipotent actions. As applications, we extend results of
Jungreis and Calegari from closed hyperbolic to finite-volume hyperbolic
manifolds:
a) Strict subadditivity of simplicial volume with respect to isometric glueing along
geodesic surfaces, and
b) nontriviality of the foliated Gromov norm for “most” foliations with two-sided
branching.
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