The bounded area class of negatively curved surfaces
Abstract
Let S be an oriented surface, possibly of infinite type, endowed with a complete Riemannian metric with pinched negative curvature. We prove that the area form defines a non-trivial class in the second bounded cohomology group of S, unless S is diffeomorphic to the disc or the cylinder. This is in sharp contrast with the n-dimensional case, n>2, where the non-triviality of the volume form in bounded cohomology is related to the Cheeger constant of the manifold. We also discuss how the bounded area class depends on the metric: we prove that, for compact surfaces, it recognizes constant curvature metrics among pinched negatively curved ones, while, even in the case of surfaces of infinite type, it does not distinguish non-isometric hyperbolic structures. More precisely, when S is compact we show that, among the negatively curved structures of fixed area, the ones with constant curvature provide the unique minimizers for the norm of the bounded area class.
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BibTeX
@misc{frigerio2026bounded,
title = {{The bounded area class of negatively curved surfaces}},
author = {Roberto Frigerio and Ervin Hadziosmanovic},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.01830},
eprint = {2609.01830},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.01830},
}
RIS
TY - UNPB
TI - The bounded area class of negatively curved surfaces
AU - Roberto Frigerio
AU - Ervin Hadziosmanovic
PY - 2026
DA - 2026/09/01
PB - arXiv
DO - 10.48550/arxiv.2609.01830
UR - https://arxiv.org/abs/2609.01830
AB - Let S be an oriented surface, possibly of infinite type, endowed with a complete Riemannian metric with pinched negative curvature. We prove that the area form defines a non-trivial class in the second bounded cohomology group of S, unless S is diffeomorphic to the disc or the cylinder. This is in sharp contrast with the n-dimensional case, n>2, where the non-triviality of the volume form in bounded cohomology is related to the Cheeger constant of the manifold. We also discuss how the bounded area class depends on the metric: we prove that, for compact surfaces, it recognizes constant curvature metrics among pinched negatively curved ones, while, even in the case of surfaces of infinite type, it does not distinguish non-isometric hyperbolic structures. More precisely, when S is compact we show that, among the negatively curved structures of fixed area, the ones with constant curvature provide the unique minimizers for the norm of the bounded area class.
ER -