弦理论中的轴子二次耦合
Quadratic Axion Couplings in String Theory
浏览论文内容
中文总结 AI 辅助
本文提出弦理论中产生轴子与规范场二次耦合的三类机制，发现该耦合普遍存在且强于QCD轴子的对应耦合，可用于探测弦理论轴子景观。
中文摘要 AI 辅助
轴子及类轴子粒子是超出标准模型的物理的引人注目的候选者。尽管许多轴子搜寻聚焦于与光子的线性耦合 $\theta F \tilde{F}$，但与电磁动能项的二次耦合 $\theta^2 F^2$ 的可能性会产生新颖的现象学和测试类轴子粒子的新机会。在这项工作中，我们提出了在弦理论中产生这种耦合的机制，这些机制可大致分为经典、微扰和非微扰三类。在基准示例中，我们发现微扰和非微扰量子贡献（如瞬子）都会产生被压低的耦合，以 $1/f^2$ 为单位时 $g \ll 1$，其中 $f$ 为轴子衰变常数，不过这些耦合很容易大于通过带电介子的圈图产生的QCD轴子的类似耦合。这些分析表明，轴子与规范场的二次耦合在弦理论中普遍存在，应作为探测弦理论轴子景观的重要内容，既适用于弦理论中动态轴子（如暗物质或暗能量）的候选者，也适用于弦理论轴子景观的谱学研究。
英文摘要
Axions and axion-like particles are a compelling candidate for physics beyond the standard model. While many axion searches are focused on the linear coupling to photons $θF \tilde{F}$, the possibility of a quadratic coupling to the electromagnetic kinetic term, $θ^2 F^2$, leads to novel phenomenology and new opportunities for testing axion-like particles. In this work we propose mechanisms for generating this coupling in string theory, which can be broadly classified as classical, perturbative, and non-perturbative. In benchmark examples, we find that both perturbative and non-perturbative quantum contributions such as instantons lead to couplings that are suppressed, $g \ll 1$ in units of $1/f^2$ where $f$ is axion decay constant, though easily larger than analogous coupling of the QCD axion that is generated through loops of charged pions. These analyses suggest that quadratic axion couplings to gauge fields are ubiquitous in string theory, and should be taken seriously as a probe of the string theory axiverse, both of string theory candidates for dynamical axions, such as dark matter or dark energy, and for spectroscopy of the string theory axiverse.
