Abstract:

The Standard Model successfully describes particle physics phenomenology. However, it is often argued that due to the presence of the so-called topological term, the strong interactions violate charge-parity (CP). The tight upper bounds on the neutron electric dipole moment would then indicate a fine-tuning problem pointing to physics beyond the Standard Model. But is that so?

To answer this question, I will explain that chiral perturbation theory as an effective model of hadrons does not uniquely specify whether there is strong CP violation or not. Thus, I reconsider topological aspects. In functional quantization, where vacuum correlators are calculated in the limit of infinite Euclidean time, integer topological sectors only emerge in the same limit. Time must therefore be taken to infinity before summing over sectors, which turns out to imply CP conservation. In canonical quantization, based on temporal gauge, no extra gauge constraint that would divide gauge transformation into disconnected equivalence classes is imposed. As a consequence, we derive that the wave functional is invariant under gauge transformations, which again implies CP conservation. No theta-vacua, that are improperly normalizable and fall afoul of the Dirac-von Neumann axioms, are hence required.

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