Novel loopdiagrammatic approach to QCD θ parameter and application to the leftright model
Abstract
When the QCD axion is absent in full theory, the strong CP problem has to be explained by an additional mechanism, e.g., the leftright symmetry. Even though treelevel QCD θ ¯ parameter is restricted by the mechanism, radiative corrections to θ ¯ are mostly generated, which leads to a dangerous neutron electric dipole moment (EDM). The ordinary method for calculating the radiative θ ¯ utilizes an equation θ ¯=−argdetm_{q}^{loop} based on the chiral rotations of complex quark masses. In this paper, we point out that when full theory includes extra heavy quarks, the ordinary method is unsettled for the extra quark contributions and does not contain its full radiative corrections. We formulate a novel method to calculate the radiative corrections to θ ¯ through a direct loopdiagrammatic approach, which should be more robust than the ordinary one. As an application, we investigate the radiative θ ¯ in the minimal leftright symmetric model. We first confirm a seminal result that twoloop level radiative θ ¯ completely vanishes (corresponding to oneloop corrections to the quark mass matrices). Furthermore, we estimate the size of a nonvanishing radiative θ ¯ at threeloop level. It is found that the resultant induced neutron EDM is comparable to the current experimental bound, and the expected size is restricted by the perturbative unitarity bound in the minimal leftright model.
 Publication:

Journal of High Energy Physics
 Pub Date:
 March 2023
 DOI:
 10.1007/JHEP03(2023)150
 arXiv:
 arXiv:2301.13405
 Bibcode:
 2023JHEP...03..150H
 Keywords:

 CP Violation;
 Electric Dipole Moments;
 LeftRight Models;
 High Energy Physics  Phenomenology;
 High Energy Physics  Experiment
 EPrint:
 32 pages, 5 figures, 2 tables