  In this note we extend previous work on massless Ramond spectra of open
strings connecting D-branes wrapped on complex manifolds, to consider D-branes
wrapped on smooth complex orbifolds. Using standard methods, we calculate the
massless boundary Ramond sector spectra directly in BCFT, and find that the
states in the spectrum are counted by Ext groups on quotient stacks (which
provide a notion of homological algebra relevant for orbifolds). Subtleties
that cropped up in our previous work also appear here. We also use the McKay
correspondence to relate Ext groups on quotient stacks to Ext groups on (large
radius) resolutions of the quotients. As stacks are not commonly used in the
physics community, we include pedagogical discussions of some basic relevant
properties of stacks.
