Vanishing conjecture for higher localised A^\widehat{A}-genera

Let Γ\Gamma be a discrete group acting properly and cocompactly on a connected spin manifold MM. Let BΓ\underline{B}\Gamma denote the classifying space for proper actions, let f ⁣:M/ΓBΓf\colon M/\Gamma\to\underline{B}\Gamma be the classifying map, and let ωΩm(M)\omega\in\Omega^m(M) be a Γ\Gamma-invariant lift of a closed differential form on the orbifold M/ΓM/\Gamma whose cohomology class is f[α]f^*[\alpha] for some αZm(BΓ,R)\alpha\in Z^m(\underline{B}\Gamma,\mathbb{R}). For each gΓg\in\Gamma, let MgM^g be the fixed-point submanifold, let ZgZ^g be the centraliser of gg, and let cgc^g be a cut-off function for the proper cocompact action of ZgZ^g on MgM^g. Define

A^g(M,ω)MgcgA^(Mg)ωMgdet(1geRN/2πi)1/2.\widehat A_{g}(M,\omega)\coloneqq\int_{M^g}c^g\cdot\frac{\widehat A(M^g)\cdot\omega|_{M^g}}{\det(1-g e^{-R^{\mathcal{N}}/2\pi i})^{1/2}}.

Vanishing conjecture for higher localised A^\widehat{A}-genera. If MM admits a Γ\Gamma-invariant Riemannian metric of positive scalar curvature, then for every closed mm-form ω\omega constructed as above and every gΓg\in\Gamma,

A^g(M,ω)=0.\widehat A_{g}(M,\omega)=0.

This is the proposed positive-scalar-curvature obstruction for proper cocompact actions, extending the torsion-free setting and incorporating fixed-point contributions from elements of Γ\Gamma; the source gives no evidence of a resolution.

Sources & referencesView supporting material

Primary source

Hao Guo and Varghese Mathai, “Higher localised A-genera for proper actions and applications”, arXiv:2108.01838 (2022).

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