Speaker
Description
In this paper, we evaluate the QCD $\theta$ angle radiatively induced at the two-loop level using the dimensional regularization with the BMHV scheme in a simplified model. When the Lagrangian is promoted into $d$-dimensional space through the dimensional regularization, evanescent operators are introduced, which break the chiral symmetry. Consequently, a parity-odd fermion loop with the BMHV scheme generates an evanescent contribution that deviates from the original chiral symmetry. We carefully classify the evanescent contribution into two types: one originating from the evanescent operator and the other directly produced by the two-loop calculation. These unphysical contributions can be removed from the renormalization equation for the QCD $\theta$ angle by re-parameterizing the angle.
