paper

Higher genus modular graph functions, string invariants, and their exact asymptotics

arXiv:1712.06135 · doi:10.1007/s00220-018-3244-3

Abstract

The concept and the construction of modular graph functions are generalized from genus-one to higher genus surfaces. The integrand of the four-graviton superstring amplitude at genus-two provides a generating function for a special class of such functions. A general method is developed for analyzing the behavior of modular graph functions under non-separating degenerations in terms of a natural real parameter . For arbitrary genus, the Arakelov Green function and the Kawazumi-Zhang invariant degenerate to a Laurent polynomial in of degree in the limit . For genus two, each coefficient of the low energy expansion of the string amplitude degenerates to a Laurent polynomial of degree in , where is the degree of homogeneity in the kinematic invariants. These results are exact to all orders in , up to exponentially suppressed corrections. The non-separating degeneration of a general class of modular graph functions at arbitrary genus is sketched and similarly results in a Laurent polynomial in of bounded degree. The coefficients in the Laurent polynomial are generalized modular graph functions for a punctured Riemann surface of lower genus.

63 pages, 8 figures; minor typos corrected in new version

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