The parity of a pair of electrons In the page 254 of Scrednicki's QFT book, it states that a pair of electrons also has negative intrinsic parity. But I think the parity of two identical particles must be one. Can someone please explain why?
 A: The intrinsic parity of a pair of particles is the product of the intrinsic parities of the particles.  The convention is that that matter particles have positive parity and antiparticles have negative parity, so a pair of matter particles should have positive intrinsic parity.
However that's not quite the entire story, because electrons must obey the exclusion principle: the total electron wavefunction must be antisymmetric under exchange.  The antisymmetry is established in the angular momentum sector. If the two electrons' spins are configured as a spin singlet, the orbital angular momentum $L$ between them must be even; if the electrons form a spin triplet, $L$ must be odd.  The parity of the orbital angular momentum wavefunctions is $(-1)^L$, so the total parity of an electron pair depends on the total spin.
This answer is different from your textbook (draft online).
The difference between his argument and mine seems to come from equation 40.15, where the parity transformation on the Dirac spinor introduces a phase factor $i\beta$ for matrix $\beta = \left(\array{0&I\\I&0}\right)$; the negative intrinsic parity for the particle-antiparticle pair comes from $(i\beta)^2=-I$.  A full explanation probably involves something sneaky with Weyl spinors.  Why not try following the derivation in equations 40.10–40.17 for a particle pair instead of an antiparticle pair?
