Novel loop-diagrammatic approach to QCD $\theta$ parameter and application to the left-right model

Junji Hisano, Teppei Kitahara, Naohiro Osamura +1

When the QCD axion is absent in full theory, the strong $CP$ problem has to be explained by an additional mechanism, e.g., the left-right symmetry. Even though tree-level QCD $\bar…