The too visible QCD axion

by Andrea Tesi

Thursday 19 Feb 2026, 13:30 → 14:30 Europe/Zurich

4/2-037 - TH meeting room (CERN)

In a very interesting recent paper, Murayama suggested a model for 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. The model suffers from 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 where the axion becomes light, finding that it is excluded by fifth-force constraints.