M24-twisted Product Expansions are Siegel Modular Forms
arXiv:1208.3453
Abstract
Cheng constructed product expansions from twists of elliptic genera of symmetric powers of K3 surfaces that are related to M_24 moonshine. We study which of them are Siegel modular forms. If the predicted level is non-composite, they are modular, and their powers can be represented as products of rescaled Borcherds products.
arXiv comment14 pages, additional data on author's homepage