Moment Polyptychs and the Equivariant Quantisation of Hypertoric Varieties
Abstract
We study the equivariant geometric quantisation of a non-compact hypertoric variety of complex dimension 2n using symplectic cutting. When the defining arrangement is cooriented so that its base region is non-empty and bounded, fibre rotation has proper moment map and produces compact Kähler orbifold cuts carrying the residual torus action. We introduce the moment polyptych of such a cut, a polytopal complex assembled from truncated arrangement regions, and show that its vertices and local lattice data determine the fixed points, tangent weights, and finite orbifold groups required for equivariant orbifold Riemann-Roch localisation. Even for a smooth hypertoric manifold, a reducible core forces every cut in the outer cut chamber to have non-trivial cyclic isotropy, while the cuts are smooth if and only if the manifold is the cotangent bundle of its distinguished compact toric subvariety, which is then a product of projective spaces. For a positive regular integral level d in the outer cut chamber, algebraic cutting identifies the cut's quantisation with a finite filtration piece of the circle-graded quantisation of the original hypertoric variety, whose successive quotients recover the individual circle-weight spaces. We prove that the higher cohomology of the pre-quantum line orbibundle vanishes at every such level, so that the localised index is the character of the actual space of sections. Finally, a residual weight x occurs at level d if and only if 𝒮(x) ≤ d, where 𝒮 is the arrangement slack function, with multiplicity binomd − 𝒮(x) + nn. Thus, each finite stage admits a weighted lattice-point description whose multiplicity function is supported on the lattice points in the support of the level-d moment polyptych.
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BibTeX
@misc{brown2026moment,
title = {{Moment Polyptychs and the Equivariant Quantisation of Hypertoric Varieties}},
author = {Benjamin C. W. Brown},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.37724},
eprint = {2610.37724},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.37724},
}
RIS
TY - UNPB
TI - Moment Polyptychs and the Equivariant Quantisation of Hypertoric Varieties
AU - Benjamin C. W. Brown
PY - 2026
DA - 2026/10/27
PB - arXiv
DO - 10.48550/arxiv.2610.37724
UR - https://arxiv.org/abs/2610.37724
AB - We study the equivariant geometric quantisation of a non-compact hypertoric variety of complex dimension 2n using symplectic cutting. When the defining arrangement is cooriented so that its base region is non-empty and bounded, fibre rotation has proper moment map and produces compact Kähler orbifold cuts carrying the residual torus action. We introduce the moment polyptych of such a cut, a polytopal complex assembled from truncated arrangement regions, and show that its vertices and local lattice data determine the fixed points, tangent weights, and finite orbifold groups required for equivariant orbifold Riemann-Roch localisation. Even for a smooth hypertoric manifold, a reducible core forces every cut in the outer cut chamber to have non-trivial cyclic isotropy, while the cuts are smooth if and only if the manifold is the cotangent bundle of its distinguished compact toric subvariety, which is then a product of projective spaces. For a positive regular integral level d in the outer cut chamber, algebraic cutting identifies the cut's quantisation with a finite filtration piece of the circle-graded quantisation of the original hypertoric variety, whose successive quotients recover the individual circle-weight spaces. We prove that the higher cohomology of the pre-quantum line orbibundle vanishes at every such level, so that the localised index is the character of the actual space of sections. Finally, a residual weight x occurs at level d if and only if 𝒮(x) ≤ d, where 𝒮 is the arrangement slack function, with multiplicity binomd − 𝒮(x) + nn. Thus, each finite stage admits a weighted lattice-point description whose multiplicity function is supported on the lattice points in the support of the level-d moment polyptych.
ER -