Abstract
We present a new mechanism to solve the strong CP problem using N ≥ 2 axions, each dynamically relaxing part of the θ parameter. At high energies M ≫ ΛQCD the SU(3)c group becomes the diagonal subgroup of an SU(3)N gauge group, and the non-perturbative effects in each individual SU(3) factor generate a potential for the corresponding axion. The vacuum is naturally aligned to ensure overline{theta} = 0 at low energies, and the masses of these axions can be much larger than for the standard QCD axion. This mechanism avoids the introduction of a discrete Z2 symmetry and associated ‘mirror’ copies of the SM fermions, and also avoids the introduction and stabilization of new light colored states to modify the running of the QCD gauge coupling found in other heavy axion models. This strengthens the motivation for axion-like particles solving the strong CP problem at points beyond the standard QCD axion curve in the (ma, fa) plane.
Highlights
We have described a novel mechanism for solving the strong CP problem
In the standard QCD axion mechanism, a spontaneously broken anomalous U(1)P Q symmetry results in an axion with a potential generated by non-perturbative effects near the scale ΛQCD
Because each individual SU(3) factor is more strongly coupled than the SM QCD at the scale M, the non-perturbative contributions to the axion potentials at the scale M can be much larger than those generated near ΛQCD for the standard QCD axion
Summary
Since we are integrating out the heavy degrees of freedom, we must consider short distance non-perturbative effects in the individual SU(3) and SU(3) factors, which will generate the shift-symmetry breaking potentials for the axions. The axions still couple to the low energy QCD GG term, and at the scale ΛQCD ∼ 1 GeV the non-perturbative SM contributions to the axion potentials will be generated. Note that the non-perturbative effects have a large effect on the axion masses in this regime, the individual gauge factors are still reasonably weakly coupled at the scale M , with αs far away from the chiral-symmetry breaking phase which would be expected to occur at αs1 0.7 − 1 [52, 53]. N − 1 axions with masses mai ∼ M 2/fi, while the mass of the axion in the SU(3) sector will still be suppressed by the chiral suppression factor, giving ma1 ∼ 10−12M 2/f1
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