- Institute for Theoretical Physics, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland
It is shown that the two-loop parity-violating five-point amplitudes for the emission of an antisymmetric tensor field and four gravitons and/or gauge bosons vanish for the heterotic string. As a result, the anomaly cancelling terms in the effective field-theoretic action in D = 10 are not renormalized by two-loop string effects. This provides an extension of the Adler-Bardeen theorem for string theory. The prospects for further extension to arbitrary genus are also discussed.
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