标题： 凝聚态衰变在辐射主导的宇宙学中 显示英文标题

标题： Condensate decay in a radiation dominated cosmology

摘要： 我们研究了大质量标量场的均匀凝聚体在宇宙辐射主导时期衰变为热平衡的无质量场的过程，该凝聚体的质量为\emph{m}。 这个模型是描述错配轴子凝聚体非平衡动力学衰变为辐射的一种\emph{代理}。 在一致的宇宙背景场量子化之后，我们得到了均匀凝聚体的因果运动方程，包括一阶有限温度自能修正。 动态重整化群被用来得到描述凝聚体振幅从介质中的无质量量子受激发射和重组而衰变的动力学的时间依赖弛豫率。 明确表明，运动方程中的简单摩擦项不能正确描述凝聚体的衰变。 在与超轻暗物质相关的超哈勃尺度下，凝聚体振幅的衰减遵循$e^{-\frac{g^2}{10} t^2\,\ln(1/mt)}$。 在亚哈勃尺度下，振幅衰减遵循$e^{-\gamma(t;T(t))/2}$，其中$T(t)=T_0/a(t)$，因此衰变率的有限温度贡献在膨胀过程中迅速消失。 一个主要结论是，描述超哈勃尺度衰变的唯象摩擦项不足以描述这种衰变过程，由于宇宙膨胀的影响，衰变函数$\gamma(t)$总是比局部摩擦项的结果\emph{更小的}更显著。 对于超轻暗物质，对宇宙膨胀敏感且局部摩擦项不适用的时间尺度要长得多。 一个摩擦项总是使亚霍布勒情况下的衰减时间尺度\emph{低估}。 显示英文摘要

摘要： We study the decay of a homogeneous condensate of a massive scalar field of mass \emph{m} into massless fields in thermal equilibrium in a radiation dominated cosmology. The model is a \emph{proxy} for the non-equilibrium dynamics of a misaligned axion condensate decaying into radiation. After consistent field quantization in the cosmological background, we obtain the causal equations of motion for a homogeneous condensate including the finite temperature self-energy corrections up to one loop. The dynamical renormalization group is implemented to obtain the time dependent relaxation rate that describes the decay dynamics of the condensate amplitude from stimulated emission and recombination of massless quanta in the medium. It is explicitly shown that a simple friction term in the equation of motion does not describe correctly the decay of the condensate. During the super-Hubble regime, relevant for ultralight dark matter, the condensate amplitude decays as $e^{-\frac{g^2}{10} t^2\,\ln(1/mt)}$. In the sub-Hubble regime the amplitude decays as $e^{-\gamma(t;T(t))/2}$ with $T(t)=T_0/a(t)$, therefore the finite temperature contribution to the decay rate vanishes fast during the expansion. A main conclusion is that a phenomenological friction term is inadequate to describe the decay in the super-Hubble regime, the decay function $\gamma(t)$ is always \emph{smaller} than that from a local friction term as a consequence of the cosmological expansion. For ultra light dark matter, the time scale during which transient dynamics is sensitive to cosmological expansion and a local friction term is inadequate, is much longer. A friction term always \emph{underestimates} the time scale of decay in the sub-Hubble case.