<p>The QCD axion is widely studied as a dark matter (DM) candidate and as a solution to the strong CP problem of the Standard Model. In conventional field-theoretic models, a much larger mass scale than the electroweak (EW) scale is typically introduced to spontaneously break Peccei-Quinn (PQ) symmetry with a large enough axion decay constant, <i>f</i><sub><i>a</i></sub>, thereby avoiding constraints from star cooling. In this paper, I propose an alternative approach to achieving the large decay constant: a PQ scalar field with a large wave function renormalization constant, analogous to a feebly coupled gauge theory. Other dimensionless parameters are <InlineEquation ID="IEq1"> <EquationSource Format="MATHML"><math display="inline"> <mi mathvariant="script">O</mi> <mfenced close=")" open="("> <mn>1</mn> </mfenced> </math></EquationSource> <EquationSource Format="TEX">\( \mathcal{O}(1) \)</EquationSource> </InlineEquation> in the unit of the EW scale for the naturalness. This framework predicts a light PQ Higgs boson with a mass ~ (EW scale)<sup>2</sup>/<i>f</i><sub><i>a</i></sub>. Exotic particles associated with the PQ anomaly are expected to have masses around the EW scale. The proposed model alleviates both the PQ quality and EW scale fine-tuning problems and introduces interesting axion-PQ Higgs cosmologies, encompassing: slim axion DM from a fat string network, heavy axion DM from PQ Higgs condensate fragmentation, PQ Higgs DM, and axion-PQ Higgs co-DM scenarios. Potential experimental signatures are explored, including fifth-force tests, DM detections, accelerator searches, and gravitational wave observations by employing lattice simulation. Possible extensions of the scenario are also discussed.</p>

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Feebly-interacting Peccei-Quinn model

  • Wen Yin

摘要

The QCD axion is widely studied as a dark matter (DM) candidate and as a solution to the strong CP problem of the Standard Model. In conventional field-theoretic models, a much larger mass scale than the electroweak (EW) scale is typically introduced to spontaneously break Peccei-Quinn (PQ) symmetry with a large enough axion decay constant, fa, thereby avoiding constraints from star cooling. In this paper, I propose an alternative approach to achieving the large decay constant: a PQ scalar field with a large wave function renormalization constant, analogous to a feebly coupled gauge theory. Other dimensionless parameters are O 1 \( \mathcal{O}(1) \) in the unit of the EW scale for the naturalness. This framework predicts a light PQ Higgs boson with a mass ~ (EW scale)2/fa. Exotic particles associated with the PQ anomaly are expected to have masses around the EW scale. The proposed model alleviates both the PQ quality and EW scale fine-tuning problems and introduces interesting axion-PQ Higgs cosmologies, encompassing: slim axion DM from a fat string network, heavy axion DM from PQ Higgs condensate fragmentation, PQ Higgs DM, and axion-PQ Higgs co-DM scenarios. Potential experimental signatures are explored, including fifth-force tests, DM detections, accelerator searches, and gravitational wave observations by employing lattice simulation. Possible extensions of the scenario are also discussed.