2,605 research outputs found
Mock Modular Mathieu Moonshine Modules
We construct super vertex operator algebras which lead to modules for
moonshine relations connecting the four smaller sporadic simple Mathieu groups
with distinguished mock modular forms. Starting with an orbifold of a free
fermion theory, any subgroup of Co_0 that fixes a 3-dimensional subspace of its
unique non-trivial 24-dimensional representation commutes with a certain N=4
superconformal algebra. Similarly, any subgroup of Co_0 that fixes a
2-dimensional subspace of the 24-dimensional representation commutes with a
certain N=2 superconformal algebra. Through the decomposition of the
corresponding twined partition functions into characters of the N=4 (resp. N=2)
superconformal algebra, we arrive at mock modular forms which coincide with the
graded characters of an infinite-dimensional Z-graded module for the
corresponding group. The Mathieu groups are singled out amongst various other
possibilities by the moonshine property: requiring the corresponding weak
Jacobi forms to have certain asymptotic behaviour near cusps. Our constructions
constitute the first examples of explicitly realized modules underlying
moonshine phenomena relating mock modular forms to sporadic simple groups.
Modules for other groups, including the sporadic groups of McLaughlin and
Higman--Sims, are also discussed.Comment: 94 pages, including 56 pages of tables; v2: updated references and
minor revisions to abstract, introduction and sections 8 and
Mathieu Moonshine and N=2 String Compactifications
There is a `Mathieu moonshine' relating the elliptic genus of K3 to the
sporadic group M_{24}. Here, we give evidence that this moonshine extends to
part of the web of dualities connecting heterotic strings compactified on K3
\times T^2 to type IIA strings compactified on Calabi-Yau threefolds. We
demonstrate that dimensions of M_{24} representations govern the new
supersymmetric index of the heterotic compactifications, and appear in the
Gromov--Witten invariants of the dual Calabi-Yau threefolds, which are elliptic
fibrations over the Hirzebruch surfaces F_n.Comment: 28 pages; v2: minor changes, published versio
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