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The level structure in quantum $K$-theory and mock theta functions

Yongbin Ruan, Ming Zhang and Yaoxiong Wen

Geometry & Topology 30 (2026) 835–882
Abstract

This is the first in a sequence of papers to develop the theory of levels in quantum K-theory and study its applications. Here, we give an adelic characterization of the range of the J-function in quantum K-theory with level structure. As an application, we prove a mirror theorem for permutation-equivariant quantum K-theory with level structures of toric varieties. In the study of the mirrors of some simple examples, we see the surprising appearance of Ramanujan’s mock theta functions.

Keywords
quantum $K$-theory, level structure, mock theta function
Mathematical Subject Classification 2010
Primary: 14N35
Secondary: 14D20, 19E08, 33D15
References
Publication
Received: 17 May 2018
Revised: 11 February 2025
Accepted: 4 May 2025
Published: 20 April 2026
Proposed: András I Stipsicz
Seconded: Mark Gross, Arend Bayer
Authors
Yongbin Ruan
Department of Mathematics
University of Michigan
Ann Arbor, MI
United States
Institute of Advanced Study for Mathematics
Zhejiang University
Hangzhou
China
Ming Zhang
Department of Mathematics
University of Michigan
Ann Arbor, MI
United States
Yaoxiong Wen
School of Mathematics
Korea Institute for Advanced Study
Seoul
South Korea

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