Vanishing of the first reduced cohomology with values in an $L^p$-representation

Abstract

We prove that the first reduced cohomology with values in a mixing Lp-representation, p larger than 1, vanishes for a class of amenable groups including connected amenable Lie groups. In particular this solves for this class of amenable groups a conjecture of Gromov saying that every finitely generated amenable group has no first reduced lp-cohomology. As a byproduct, we prove a conjecture by Pansu. Namely, the first reduced Lp-cohomology on homogeneous, closed at infinity, Riemannian manifolds vanishes. We also prove that a Gromov hyperbolic geodesic metric measure space with bounded geometry admitting a bi-Lipschitz embedded 3-regular tree has non-trivial first reduced Lp-cohomology for large enough p. Combining our results with those of Pansu, we characterize Gromov hyperbolic homogeneous manifolds: these are the ones having non-zero first reduced Lp-cohomology for some p larger than 1.

arXiv comment20 pages, correction: minor changes (introduction), corrections: we improved the redaction (in particular, adding more details to the proofs), and showed a more general statement for hyperbolic spaces

References in corpus (3)

• Isometric group actions on Hilbert spaces: growth of cocycles
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• Mixing, malnormal subgroups and cohomology in degree one
• Graphs of bounded degree and the $p$-harmonic boundary
• Vanishing of ${\ell }^p$-cohomology and transportation cost
• Aspects de la géométrie des groupes