标题： 宇宙双折射来自CP破坏的轴子相互作用 显示英文标题

标题： Cosmic Birefringence from CP-Violating Axion Interactions

摘要： 我们研究了由超轻轴子场产生的宇宙双折射信号，该轴子场除了通常的CP守恒光子耦合外，还具有与大块标准模型物质微小CP破坏耦合。 从再结合到现在的场真空期望值的变化导致了CMB线性偏振平面在整个天空中的频率无关旋转。 虽然许多先前的方法依赖于轴子从一个大的初始期望值滚动，但本工作中考虑的耦合无论初始条件如何都能稳健地产生双折射信号，通过从宇宙核子密度中产生场来实现。 我们利用Planck和WMAP数据中双折射角度测量的结果，对这种单极-偶极相互作用进行了限制，这些限制比现有约束提高了多达三个数量级。 我们还讨论了该模型的UV完备化以及可能避免轴子质量精细调节的策略。 显示英文摘要

摘要： We explore the cosmic birefringence signal produced by an ultralight axion field with a small CP-violating coupling to bulk SM matter in addition to the usual CP-preserving photon coupling. The change in the vacuum expectation value of the field between recombination and today results in a frequency-independent rotation of the plane of CMB linear polarization across the entire sky. While many previous approaches rely on the axion rolling from a large initial expectation value, the couplings considered in this work robustly generate the birefringence signal regardless of initial conditions, by sourcing the field from the cosmological nucleon density. We place bounds on such monopole-dipole interactions using measurements of the birefringence angle from Planck and WMAP data, which improve upon existing constraints by up to three orders of magnitude. We also discuss UV completions of this model, and possible strategies to avoid fine-tuning the axion mass.