标题： 由膨胀驱动的量子相变产生的轴子暗物质 显示英文标题

标题： Axion dark matter from inflation-driven quantum phase transition

摘要： 我们提出了一种新机制，用于从膨胀涨落中产生轴子暗物质。膨胀期间的量子涨落通过轴子动能项与膨胀子的耦合而增强，我们将这种耦合参数化为轴子运动方程中的有效曲率$\kappa$。非零曲率破坏了轴子功率谱的标度不变性，驱动了一个以$\kappa$为序参量的量子相变。轴子功率谱与共动视界的逆幂次成正比，指数为$\kappa$。对于正的$\kappa$，光谱呈现红倾，导致轴子丰度在膨胀过程中随着共动视界缩小而呈指数增长。这种增强即使在轴子超轻质量的情况下，也足以使其成为整个暗物质遗迹丰度的一部分。我们的机制预测的参数空间与通常的错配机制显著不同。它允许具有更低衰减常数和因此更大与标准模型粒子耦合的类轴子粒子暗物质。大部分参数空间可以通过未来包括腔体探测器、核钟、CASPEr 和 CMB-S4 等实验来探测。我们还可以生成比错配机制更重的QCD轴子暗物质。 显示英文摘要

摘要： We propose a new mechanism to produce axion dark matter from inflationary fluctuations. Quantum fluctuations during inflation are strengthened by a coupling of the axion kinetic term to the inflaton, which we parametrize as an effective curvature $\kappa$ in the axion equation of motion. A nonvanishing curvature breaks the scale invariance of the axion power spectrum, driving a quantum phase transition with $\kappa$ as the order parameter. The axion power spectrum is proportional to the inverse comoving horizon to the power of $\kappa$. For positive $\kappa$ the spectrum gets a red tilt, leading to an exponential enhancement of the axion abundance as the comoving horizon shrinks during inflation. This enhancement allows sufficient axion production to comprise the entire dark matter relic abundance despite the ultralight mass. Our mechanism predicts a significantly different parameter space from the usual misalignment mechanism. It allows for axion-like particle dark matter with a much lower decay constant and thus a larger coupling to Standard Model particles. Much of the parameter space can be probed by future experiments including haloscopes, nuclear clocks, CASPEr, and CMB-S4. We can also generate heavier QCD axion dark matter than the misalignment mechanism.