PreprintCC BY 4.0arXiv
Intrinsic Non-Reductive Geometric Invariant Theory and Moduli Spaces of Principal Bundles with Non-Reductive Structure Groups
Abstract
We prove the existence of moduli spaces for algebraic stacks with a weak action of Θ= [𝔸1/𝔾m] (including stacks of filtered objects and unstable Θ-strata) for which the center admits a good moduli space and the retraction to the center has flat, finitely presented relative inertia, providing a stack-intrinsic generalization of the existence of non-reductive Geometric Invariant Theory quotients. As an application, we construct quasi-projective coarse moduli spaces of principal bundles over a smooth projective curve with non-reductive structure groups, including moduli spaces of Ramanathan unstable principal bundles of fixed Harder--Narasimhan type.
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BibTeX
@misc{cooper2026intrinsic,
title = {{Intrinsic Non-Reductive Geometric Invariant Theory and Moduli Spaces of Principal Bundles with Non-Reductive Structure Groups}},
author = {George Cooper and Ludvig Modin},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.38837},
eprint = {2610.38837},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.38837},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Intrinsic Non-Reductive Geometric Invariant Theory and Moduli Spaces of Principal Bundles with Non-Reductive Structure Groups
AU - George Cooper
AU - Ludvig Modin
PY - 2026
DA - 2026/10/28
PB - arXiv
DO - 10.48550/arxiv.2610.38837
UR - https://arxiv.org/abs/2610.38837
AB - We prove the existence of moduli spaces for algebraic stacks with a weak action of Θ= [𝔸^1/𝔾_m] (including stacks of filtered objects and unstable Θ-strata) for which the center admits a good moduli space and the retraction to the center has flat, finitely presented relative inertia, providing a stack-intrinsic generalization of the existence of non-reductive Geometric Invariant Theory quotients. As an application, we construct quasi-projective coarse moduli spaces of principal bundles over a smooth projective curve with non-reductive structure groups, including moduli spaces of Ramanathan unstable principal bundles of fixed Harder--Narasimhan type.
ER -