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arXiv · 2507.15935

Strong CP from a Hidden Chiral Condensate

Csaba Csáki·Samuel Homiller·Taewook Youn
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Abstract

Models which solve the strong CP problem by employing discrete spacetime symmetries generically suffer fine-tuning and quality problems. We demonstrate that these issues are greatly ameliorated when the only source of spontaneous CP breaking is from the chiral condensate of a strongly coupled hidden sector. This is shown explicitly in a model with the SM extended by a vector-like quark family and a complex scalar portal to QCD-like dark sector with $N_f$ families of dark fermions that confines at a high scale. The dark pions of the hidden sector are natural dark matter candidates, with the correct relic abundance obtained via freeze-in. These "confining" Nelson-Barr solutions connect phenomenological questions regarding the strong CP problem to recent developments in the understanding of confining gauge theories, and present ample room for further model building.

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Csaba Csáki, Samuel Homiller, Taewook Youn. 2025-07-21. Strong CP from a Hidden Chiral Condensate. https://doi.org/10.1007/jhep03(2026)220

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