My question concerns a integral and why it vanishes:(adsbygoogle = window.adsbygoogle || []).push({});

-nη^{I}^{J}1/2π ∫_{0}^{2π}dσ e^{i(m+n)σ}=-nη^{I}^{J}delta_{m+n=0}

Just to justify why this should be on the beyond the standard model forum, this is part of a calulation concerning the comutators of the alpha modes.

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# Integral operation

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