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Home > Physical Review D (APS) > Does chiral perturbation theory rule out QCD-based solutions to the strong <math><mi>C</mi><mi>P</mi></math> problem? |

Cohen, Thomas D. (Department of Physics and the Maryland Center for Fundamental Physics University of Maryland, 20742 Maryland, USA)

07 May 2019

**Abstract: **The conventional view is that a solution of the strong $CP$ problem lies beyond QCD. A strong argument supporting this view is that the chiral expansion shows that observables depend on theta (unless a quark mass is zero); this eliminates the possibility that theta is physically irrelevant and appears to necessitate an explanation beyond the standard model. However, scenarios that solve the strong $CP$ problem that are consistent with known chiral behavior exist; in these, QCD becomes nonviable as a theory for nonzero theta. Such scenarios appear to be compatible with lattice studies of the topological susceptibility.

**Published in: ****Physical Review D 99 (2019)**
**Published by: **APS

**DOI: **10.1103/PhysRevD.99.094007

**arXiv: **1811.04833

**License: **CC-BY-4.0