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arXiv · 2502.13050

A Hopf index for isotropic sections of orthogonal bundles

Martijn Kool·Jeongseok Oh·Jørgen Vold Rennemo·Richard P Thomas
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Abstract

The Hopf index equates the multiplicity of a zero of a section of a vector bundle with a winding number. We give eight analogues for isotropic sections of bundles with quadratic form. There are applications to cosection localised virtual cycles and to DT$^4$ virtual cycles.

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Martijn Kool, Jeongseok Oh, Jørgen Vold Rennemo, Richard P Thomas. 2025-02-18. A Hopf index for isotropic sections of orthogonal bundles. https://doi.org/10.1093/imrn%2Frnag077

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