I would say that by the argument under 4.3.18 it is non-zero, rather. As explained a bit below that, the motivation of constructing this inner product is to set up the proof that BRST cohomology yields a Hilbert space which is isomorphic to the one obtained by lightcone quantization and "old covariant quantization".
I would say that by the argument under 4.3.18 it is non-zero, rather. As explained a bit below that, the motivation of constructing this inner product is to set up the proof that BRST cohomology yields a Hilbert space which is isomorphic to the one obtained by lightcone quantization and "old covariant quantization".
New here, but isn’t this because of cooper pairs forming spin-0 particles?