具有魅夸克耦合的自然质量安全GeV轴子
Naturally quality-safe GeV axion with charm coupling
浏览论文内容
中文总结 AI 辅助
研究GeV尺度QCD轴子的结构同位旋问题，通过将PQ标量与魅夸克耦合并降低$m_\phi$解决问题，模型预测$\Delta N_{\rm eff}$及$B\to K\sigma$过程分支比，在可行窗口满足多类约束。
中文摘要 AI 辅助
GeV尺度的QCD轴子面临结构同位旋问题，其佩切伊 - 奎因（PQ）对称性被 QCD 凝聚在$f_a\sim\mathcal{O}(1)$GeV 打破，PQ 赝标量与轻夸克耦合破坏了$\mathrm{SU}(2)$同位旋。我们表明将 PQ 标量与魅夸克耦合可消除此违反，降低$m_\phi\sim 3 - 4$MeV 使魅夸克汤川耦合$\kappa_c\propto m_\phi$微扰。所得$f_a\sim\text{GeV}\ll M_{\rm Pl}$解决了轴子质量问题。该模型预测$m_\phi\sim 3$MeV 时$\Delta N_{\rm eff}\sim -0.1$，$B\to K\sigma$企鹅过程预测$\mathrm{BR}\sim 2\times 10^{-5}$。在$m_\phi\sim 3 - 4$MeV 可行窗口满足所有十类实验、天体物理和宇宙学约束。
英文摘要
The GeV-scale QCD axion -- where Peccei-Quinn (PQ) symmetry is broken by the QCD condensate at $f_a\sim\mathcal{O}(1)$~GeV -- faces a structural isospin problem: the PQ spurion coupling to light quarks ($u,d,s$) breaks $\mathrm{SU}(2)$ isospin, generating an unacceptable $\sim 15\%$ $π^0$--$π^\pm$ mass splitting. We show that coupling the PQ scalar to the charm quark instead eliminates this violation entirely, and lowering $m_ϕ\sim 3$--$4$~MeV makes the charm Yukawa $κ_c\propto m_ϕ$ perturbative ($κ_c<1$). The resulting $f_a\sim\text{GeV}\ll M_{\rm Pl}$ solves the axion quality problem: even the lowest-dimension $d=6$ Planck-suppressed operator gives $m_{\rm PQ}/m_a\sim 10^{-14}$, without any additional symmetry. The model predicts a distinctive {\it negative} $ΔN_{\rm eff}\sim -0.1$ for $m_ϕ\sim 3$~MeV, testable by CMB-S4. The $B\to Kσ$ penguin predicts $\mathrm{BR}\sim 2\times 10^{-5}$, consistent with the Belle~II evidence for $B^+\to K^+ν\barν$ at $(2.3\pm0.7)\times 10^{-5}$~\cite{BelleII:2024knv}. All ten classes of experimental, astrophysical, and cosmological constraints are satisfied in the viable window $m_ϕ\sim 3$--$4$~MeV, with the $B_s$ mixing constraint pending a dedicated lattice calculation.
