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By leveraging the physics of the Higgs branch, we argue that the conformal central charges $a$and $c$of an arbitrary 4D $\mathcal{N}=2$superconformal field theory (SCFT) are rational numbers. Our proof of the rationality of $c$is conditioned on a well-supported conjecture about how the Higgs branch of an SCFT is encoded in its protected chiral algebra. To establish the rationality of $a$, we further rely on a widely believed technical assumption on the high-temperature limit of the superconformal index. Published by the American Physical Society2024 

Motivated by the appearance of penumbral moonshine, and by evidence that penumbral moonshine enjoys an extensive relationship to generalized monstrous moonshine via infinite products, we establish a general construction in this work which uses singular theta lifts and a concrete construction at the level of modules for a finite group to translate between moonshine in weight one-half and moonshine in weight zero. This construction serves as a foundation for a companion paper in which we explore the connection between penumbral Thompson moonshine and a special case of generalized monstrous moonshine in detail. 

The monster sporadic group is the automorphism group of a central charge $c=24$ vertex operator algebra (VOA) or meromorphic conformal field theory (CFT). In addition to its $c=24$ stress tensor $T(z)$, this theory contains many other conformal vectors of smaller central charge; for example, it admits $48$ commuting $$c=\frac12$$ conformal vectors whose sum is $T(z)$. Such decompositions of the stress tensor allow one to construct new CFTs from the monster CFT in a manner analogous to the Goddard-Kent-Olive (GKO) coset method for affine Lie algebras. We use this procedure to produce evidence for the existence of a number of CFTs with sporadic symmetry groups and employ a variety of techniques, including Hecke operators and modular linear differential equations, to compute the characters of these CFTs. Our examples include (extensions of) nine of the sporadic groups appearing as subquotients of the monster, as well as the simple groups $${}^2\tsl{E}_6(2)$$ and $$\tsl{F}_4(2)$$ of Lie type. Many of these examples are naturally associated to McKay's $$\widehat{E_8}$$ correspondence, and we use the structure of Norton's monstralizer pairs more generally to organize our presentation.