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arXiv · 2602.10057

The Too Visible QCD Axion

Luca Di Luzio·Michele Redi·Alessandro Strumia·Andrea Tesi·Arsenii V. Titov
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Abstract

Murayama proposed a GeV-scale axion theory where the up-quark mass term is generated dynamically by the QCD chiral condensate, spontaneously breaking a Peccei-Quinn symmetry. It predicts a too large mass splitting between neutral and charged pions. Trying to solve this problem we explore extensions. Despite some partial improvements, we identify a structural obstruction: the new Peccei-Quinn spurion breaks the accidental isospin symmetry of the chiral Lagrangian, leading to an enhanced higher-order operator. As a consequence, pion scatterings too are distorted. We also examine the limit in which the axion becomes light, finding that it is excluded by fifth-force constraints.

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Luca Di Luzio, Michele Redi, Alessandro Strumia, Andrea Tesi, Arsenii V. Titov. 2026-02-10. The Too Visible QCD Axion. https://arxiv.org/abs/2602.10057

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