English

Higher Width Moonshine

Representation Theory 2022-06-22 v3 Number Theory

Abstract

\textit{Weak moonshine} for a finite group GG is the phenomenon where an infinite dimensional graded GG-module VG=nVG(n)V_G=\bigoplus_{n\gg-\infty}V_G(n) has the property that its trace functions, known as McKay-Thompson series, are modular functions. Recent work by DeHority, Gonzalez, Vafa, and Van Peski established that weak moonshine holds for every finite group. Since weak moonshine only relies on character tables, which are not isomorphism class invariants, non-isomorphic groups can have the same McKay-Thompson series. We address this problem by extending weak moonshine to arbitrary width sZ+s\in\mathbb{Z}^+. For each 1rs1\leq r\leq s and each irreducible character χi\chi_i, we employ Frobenius' rr-character extension χi(r) ⁣:G(r)C\chi_i^{(r)} \colon G^{(r)}\rightarrow\mathbb{C} to define \textit{width rr McKay-Thompson series} for VG(r):=VG××VGV_G^{(r)}:=V_G\times\cdots\times V_G (rr copies) for each rr-tuple in G(r):=G××GG^{(r)}:=G\times\cdots\times G (rr copies). These series are modular functions which then reflect differences between rr-character values. Furthermore, we establish orthogonality relations for the Frobenius rr-characters, which dictate the compatibility of the extension of weak moonshine for VGV_G to width ss weak moonshine.

Keywords

Cite

@article{arxiv.1807.07210,
  title  = {Higher Width Moonshine},
  author = {Madeline Locus Dawsey and Ken Ono},
  journal= {arXiv preprint arXiv:1807.07210},
  year   = {2022}
}

Comments

Versions 2 and 3 address comments from the referees

R2 v1 2026-06-23T03:06:41.689Z