QM Research Seminar: Periods on super Riemann surfaces

Speaker: Nadia Ott (University of Southern Denmark)


Abstract:

D’Hoker and Phong’s calculation of the genus g = 2 superstring amplitude uses, in a crucial way, a projection from genus g = 2 supermoduli space to its underlying reduced space. They define this projection using a formula for the genus g = 2 super period matrix. Witten generalized their formula for the super period matrix to higher genus g and found that the super period matrix may develop a pole along a particular divisor in supermoduli space if g ≥ 11. This divisor is commonly called the bad divisor. Witten also considered super period matrices on super Riemann surfaces with a nonzero number of Ramond punctures (note: the word puncture is a bit of a misnomer). He found that in the presence of Ramond punctures, a closed one form has, in addition to the usual 2g ”even” periods (defined by integrals over one cycle in homology), 2r fermionic periods. The fermionic periods of one form w are certain constants appearing in the restriction of w to the Ramond divisor. In joint work with Ron Donagi, we identify the 2r fermionic periods of w with the residues of a particular global section of the twisted spin structure on the underlying curve. As in the unpunctured case, the super period matrix with Ramond punctures may develop a singularities as we vary over supermoduli space. Using this identification of the fermionic periods in terms of residues, we explicitly describe this bad locus in supermoduli space.