In Polchinski's textbook String Theory, section 2.8, the author argues that the unit operator 1 corresponds to the vacuum state, and ∂Xμ is holomorphic inside couture Q in figure 2.6(b), so operators αμm with m>=0 vanishes.
I am a bit confused about why ∂Xμ has no pole inside the contour. Before this section ∂Xμ always has the singularity part (1/zm). Therefore would it be possible for you to give a more mathematical argument what condition requires ∂Xμ having no poles in this case?
Thanks a lot for your time!
This post imported from StackExchange Physics at 2014-04-14 16:20 (UCT), posted by SE-user Han Yan