The age grading and the Chen-Ruan cup product

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We prove that the obstruction bundle used to define the cup-product in Chen–Ruan cohomology has a simple representation-theoretic description. The key quantities in this description are the age gradings or degree-shifting numbers of the representations of the local groups of the orbifold. We obtain a Künneth Theorem for Chen–Ruan cohomology as a direct consequence of an elementary property of the age grading, and explain how several other results, including associativity of the cup product, can be proved in a similar way.
Original languageEnglish
Pages (from-to)868-878
Number of pages11
JournalBulletin of the London Mathematical Society
Issue number5
Early online date18 Jun 2010
Publication statusPublished - Oct 2010


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