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Heterotic versus Type I

C. Bachas

hep-tharXiv:hep-th/9710102

Abstract

I compare the calculations of special F4 and R4 terms in the (toroidally-compactified) heterotic and type-I effective actions. Besides checking duality, this elucidates the quantitative rules of D-brane calculus. I explain in particular (a) why D-branes do not run in loops, and (b) how their instanton contributions arise from orbifold fixed points of their moduli space. The instanton sum has a simple representation as a sum of the elliptic genera of matrix models.

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