English

To be or not to be local

Number Theory 2026-06-27 v1 Algebraic Geometry

Abstract

Let pp be a prime number and KK a finite unramified extension of Qp\mathbf{Q}_p. For a smooth representation π\pi of GL2(K)\mathrm{GL}_2(K) occurring in some Hecke eigenspace of the mod pp cohomology of a Shimura curve, we explore different strategies (inspired by the case K=QpK=\mathbf{Q}_p) to attack the locality question: does π\pi depend only on the underlying 22-dimensional representation ρ\overline{\rho} of Gal(K/K){\rm Gal}(\overline K/K)? In particular when [K:Qp]=2[K:\mathbf{Q}_p]=2, crucially using perfectoid geometry, we associate to ρ\overline{\rho} an infinite-dimensional mod pp smooth representation of (K×K01)\begin{pmatrix}K^\times&K\\0&1\end{pmatrix} which we hope is the restriction to (K×K01)\begin{pmatrix}K^\times&K\\0&1\end{pmatrix} of the (irreducible) supersingular subquotient of π\pi.

Cite

@article{arxiv.2606.28818,
  title  = {To be or not to be local},
  author = {Christophe Breuil and Florian Herzig and Yongquan Hu and Karol Koziol and Stefano Morra and Benjamin Schraen and Sug Woo Shin},
  journal= {arXiv preprint arXiv:2606.28818},
  year   = {2026}
}
R2 v1 2026-07-22T20:14:22.681Z