The residual map as a stratified fibration over the resonance arrangement
Abstract
Given a stratum ℋ(μ) of meromorphic one-forms on a Riemann surface with prescribed orders of zeros and poles, the residual map assigns to each differential the collection of its residues at the poles. In this paper, we prove that the residual map is a locally trivial topological fibration over each open flat of the stratification induced by the resonance arrangement. To give an algebro-geometric proof of this result, we introduce a refined compactification of the projectivized stratum ℙℋ(μ), namely the moduli space of residue-aligned multi-scale differentials RAMS(μ). We prove that the projectivized residual map extends to RAMS(μ) as a stratified fibration over the projectivized resonance arrangement, thereby yielding a resolution of the projectivized residual map. This approach naturally extends to the analogue of the residual map for strata of k-differentials. Complementing the algebro-geometric approach, we also develop a flat-geometric point of view. In genus zero, each isoresidual fiber carries a canonical higher-dimensional analogue of a translation structure. These fibers admit a metric completion whose boundary has a modular interpretation in terms of the WYSIWYG compactification, for which we provide explicit local models. Isoresidual fibers admit a polyhedral cell decomposition whose geometry varies linearly with the underlying configuration of residues in period coordinates. Degenerations of these cells occur precisely when resonance conditions are satisfied, providing a geometric proof that the residual map is a stratified fibration. Finally, certain isoresidual fibers admit natural interpretations as Hurwitz spaces of branched covers, yielding unexpected homeomorphisms between moduli spaces of covers with prescribed ramification profiles.
Related
BibTeX
@misc{chen2026residual,
title = {{The residual map as a stratified fibration over the resonance arrangement}},
author = {Dawei Chen and Scott Mullane and Nick Salter and Guillaume Tahar},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.07499},
eprint = {2611.07499},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.07499},
}
RIS
TY - UNPB
TI - The residual map as a stratified fibration over the resonance arrangement
AU - Dawei Chen
AU - Scott Mullane
AU - Nick Salter
AU - Guillaume Tahar
PY - 2026
DA - 2026/11/05
PB - arXiv
DO - 10.48550/arxiv.2611.07499
UR - https://arxiv.org/abs/2611.07499
AB - Given a stratum ℋ(μ) of meromorphic one-forms on a Riemann surface with prescribed orders of zeros and poles, the residual map assigns to each differential the collection of its residues at the poles. In this paper, we prove that the residual map is a locally trivial topological fibration over each open flat of the stratification induced by the resonance arrangement. To give an algebro-geometric proof of this result, we introduce a refined compactification of the projectivized stratum ℙℋ(μ), namely the moduli space of residue-aligned multi-scale differentials RAMS(μ). We prove that the projectivized residual map extends to RAMS(μ) as a stratified fibration over the projectivized resonance arrangement, thereby yielding a resolution of the projectivized residual map. This approach naturally extends to the analogue of the residual map for strata of k-differentials. Complementing the algebro-geometric approach, we also develop a flat-geometric point of view. In genus zero, each isoresidual fiber carries a canonical higher-dimensional analogue of a translation structure. These fibers admit a metric completion whose boundary has a modular interpretation in terms of the WYSIWYG compactification, for which we provide explicit local models. Isoresidual fibers admit a polyhedral cell decomposition whose geometry varies linearly with the underlying configuration of residues in period coordinates. Degenerations of these cells occur precisely when resonance conditions are satisfied, providing a geometric proof that the residual map is a stratified fibration. Finally, certain isoresidual fibers admit natural interpretations as Hurwitz spaces of branched covers, yielding unexpected homeomorphisms between moduli spaces of covers with prescribed ramification profiles.
ER -