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The rational homology of quotients of the curve complex
Abstract
Let mathopModg,n be the mapping class group of a genus-g surface with n punctures and let πg,n be its curve complex. For a finite-index subgroup G < mathopModg,n, Boggi proved that HΜk(πg,n/G;β) = 0 for g+n β« k. This plays an important role in the work of Putman-Wieland on the virtual first Betti number of mathopModg,n. The proof of Boggi's theorem uses mixed Hodge theory and is embedded in his flawed paper purporting to show that the mapping class group has the congruence subgroup property. We give a detailed exposition of Boggi's proof aimed at geometric topologists.
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BibTeX
@misc{putman2026rational,
title = {{The rational homology of quotients of the curve complex}},
author = {Andrew Putman},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.10775},
eprint = {2610.10775},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.10775},
}
RIS
TY - UNPB
TI - The rational homology of quotients of the curve complex
AU - Andrew Putman
PY - 2026
DA - 2026/10/07
PB - arXiv
DO - 10.48550/arxiv.2610.10775
UR - https://arxiv.org/abs/2610.10775
AB - Let mathopMod_g,n be the mapping class group of a genus-g surface with n punctures and let π_g,n be its curve complex. For a finite-index subgroup G < mathopMod_g,n, Boggi proved that HΜ_k(π_g,n/G;β) = 0 for g+n β« k. This plays an important role in the work of Putman-Wieland on the virtual first Betti number of mathopMod_g,n. The proof of Boggi's theorem uses mixed Hodge theory and is embedded in his flawed paper purporting to show that the mapping class group has the congruence subgroup property. We give a detailed exposition of Boggi's proof aimed at geometric topologists.
ER -