Enhanced EDMs from Small Instantons

Abstract

We show that models in which the strong $CP$ problem is solved by introducing an axion field with a mass enhanced by non-QCD UV dynamics at a scale ${\Lambda }_{\mathrm{SI}}$ exhibit enhanced sensitivity to external sources of $CP$ violation. In the presence of higher-dimensional $CP$-odd sources at a scale ${\Lambda }_{\mathrm{CP}}$, the same mechanisms that enhance the axion mass also modify the axion potential, shifting the potential minimum by a factor $\propto {\Lambda }_{\mathrm{SI}}^2/{\Lambda }_{\mathrm{CP}}^2$. This phenomenon of $CP$-violation enhancement, which puts stringent constraints on the scale of new physics, is explicitly demonstrated within a broad class of "small instanton" models with $CP$-odd sources arising from the dimension-six Weinberg gluonic and four-fermion operators. We find that for heavy axion masses $\gtrsim 100$MeV, arising from new dynamics at ${\Lambda }_{\mathrm{SI}}\lesssim 10^{10}$GeV, $CP$ violation generated up to the Planck scale can be probed by future electric dipole moment experiments.

21 pages, 4 figures; v2: version published in PRD

References in corpus (3)

• Measurement of the permanent electric dipole moment of the neutron
• Anomalous solutions to the strong CP problem
• Do Minimal Parity Solutions to the Strong CP Problem Work?

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• ALP-ine quests at the LHC: hunting axion-like particles via peaks and dips in $t\bar{t}$ production
• Finding BSM Needles in Electromagnetic Haystacks at DUNE
• Weak Scale Triggers in the SMEFT