2003/08/07 by Matthew Ando, Ando, Matthew, Christopher P. French +1
Mathematics · #55N34 #58J26 #Algebraic Topology (math.AT) #FOS: Mathematics #math.AT #msc:55N34 #msc:58J26
paper · pdf · doi:10.48550/arxiv.math/0308068
arxiv created 2003/08/07 · arxiv updated 2009/12/01
The first purpose of this paper is to examine the relationship between equivariant elliptic genera and orbifold elliptic genera. We apply the character theory of Hopkins et. al. to the Borel-equivariant genus associated to the sigma orientation of Ando-Hopkins-Strickland to define an orbifold genus for certain total quotient orbifolds and supersingular elliptic curves. We show that our orbifold genus is given by the same sort of formula as the orbifold ``two-variable'' genus of Dijkgraaf et al. In the case of a finite cyclic orbifold group, we use the characteristic series for the two-variable genus to define an analytic equivariant genus in Grojnowski's equivariant elliptic cohomology, and we show that this gives precisely the orbifold two-variable genus. The second purpose of this paper is to study the effect of varying the BU<6>-structure in the Borel-equivariant sigma orientation. We show that varying the BU<6>-structure by a class in the third cohomology of the orbifold group produces discrete torsion in the sense of Vafa. This result was first obtained by Sharpe, for a different orbifold genus and using different methods.