Higher Width Moonshine


Abstract in English

textit{Weak moonshine} for a finite group $G$ is the phenomenon where an infinite dimensional graded $G$-module $$V_G=bigoplus_{ngg-infty}V_G(n)$$ 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 $sinmathbb{Z}^+$. For each $1leq rleq s$ and each irreducible character $chi_i$, we employ Frobenius $r$-character extension $chi_i^{(r)} colon G^{(r)}rightarrowmathbb{C}$ to define textit{width $r$ McKay-Thompson series} for $V_G^{(r)}:=V_Gtimescdotstimes V_G$ ($r$ copies) for each $r$-tuple in $G^{(r)}:=Gtimescdotstimes G$ ($r$ copies). These series are modular functions which then reflect differences between $r$-character values. Furthermore, we establish orthogonality relations for the Frobenius $r$-characters, which dictate the compatibility of the extension of weak moonshine for $V_G$ to width $s$ weak moonshine.

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