QCD轴子等曲率问题的一块垫脚石方案
A Stepping Stone Solution to the QCD Axion Isocurvature Problem
浏览论文内容
中文总结 AI 辅助
本文提出“垫脚石”方案，通过引入暴胀结束前的中间PQ破缺真空，缓解QCD轴子等曲率问题中PQ标度变化带来的参数共振，实现更温和的层级差距。
中文摘要 AI 辅助
我们提出了一种“垫脚石”实现方案，用于解决QCD轴子等曲率问题中变化的Peccei Quinn（PQ）标度。在传统实现中，在高标度暴胀期间抑制等曲率扰动需要很大的暴胀期PQ标度，而随后向更小的晚期真空演化的过程可能引发参数共振和PQ对称性的非热恢复。我们通过引入一个在暴胀结束前达到的中间PQ破缺真空来缓解这一矛盾，使得随后向现今PQ标度的演化仅跨越中等层级差距。真空结构由辐射效应产生：PQ标量场与带PQ电荷的费米子之间的Yukawa耦合在高标度下驱动四次耦合为负，同时保持其在较低标度下为正。一个正的维度六算符稳定了大场最小值，而正的低能四次耦合与二次项共同产生了中间真空。我们研究了两种机制，其中滚动的暴胀子移除大场最小值，要么通过扫描隐藏的非阿贝尔规范耦合，要么直接扫描Yukawa耦合。在两种情况下，PQ场在暴胀期间、CMB模式退出视界之后被释放向中间真空。我们展示了基准区域，其中对暴胀扇区的反作用可忽略且真空隧穿受到抑制，并表明该构造允许比依赖于变化PQ标度的传统实现更小的层级差距的四次耦合和高维耦合。其基本逻辑可能对额外维或弦论轴子有类比之处，在这些情形中有效轴子衰变常数由几何模控制，尽管在受控的模势中实现所需的中间真空并非易事。
英文摘要
We propose a ''stepping stone'' realization of the varying Peccei Quinn (PQ) scale solution to the QCD axion isocurvature problem. In conventional implementations, suppressing isocurvature during high scale inflation requires a large inflationary PQ scale, while the subsequent evolution toward the much smaller late time vacuum can induce parametric resonance and nonthermal restoration of the PQ symmetry. We ameliorate this tension by introducing an intermediate PQ-breaking vacuum that is reached before the end of inflation, so that the later evolution to the present day PQ scale spans only a moderate hierarchy. The vacuum structure arises radiatively: a Yukawa coupling between the PQ scalar and PQ-charged fermions drives the quartic coupling negative at high scales while keeping it positive at lower scales. A positive dimension six operator then stabilizes a large field minimum, while the positive low energy quartic together with the quadratic terms generates the intermediate vacuum. We study two mechanisms in which the rolling inflaton removes the large field minimum, either by scanning a hidden non-Abelian gauge coupling or by directly scanning the Yukawa coupling. In both cases the PQ field is released toward the intermediate vacuum during inflation, after CMB modes have exited the horizon. We exhibit benchmark regions with subdominant backreaction on the inflationary sector and suppressed vacuum tunneling, and show that the construction permits substantially less hierarchical quartic and higher-dimensional couplings than conventional realizations that depend on a varying PQ scale. The underlying logic may have analogues for extra-dimensional or string axions, where the effective axion decay constant is controlled by geometric moduli, although realizing the required intermediate vacuum in a controlled modulus potential is nontrivial.
发表机构
- Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma（俄克拉荷马大学霍默·L·道奇物理与天文学系）
机构由 AI 辅助整理，请以论文原文为准。
