论文标题
布朗轴状颗粒
Brownian Axion-like particles
论文作者
论文摘要
我们通过获得其降低的密度矩阵，研究了伪尺度轴状粒子（ALP）的非平衡动力学，该动力学弱耦合到热平衡的自由度。 Its time evolution is determined by the in-in effective action which we obtain to leading order in the (ALP) coupling but to \emph{all orders} in the couplings of the bath to other fields within or beyond the standard model. （ALP）运动的有效运动方程是遵守波动耗散关系的噪声和摩擦内核的兰格文方程。 ````未对准''初始条件都产生了阻尼的相干振荡，但是，（ALP）种群增加了用浴缸的热化。结果，能量密度具有未对准的冷成分的混合物和热量的热成分，其比例与时间$ $（冷）\，e^{ - γt}+（热）\，（1-e^{ - γt}）$混合在一起，提供了一种寒冷的效果，可以在寒冷的情况下进行寒冷的效果。作为一个具体示例，我们将（ALP）-photon耦合$ g a \ vec {e} \ cdot \ cdot \ vec {b} $达到最低顺序，从重组开始有效。对于$ t \ gg m_a $，长波长放松率基本上增强了$γ_t= \ frac {g^2 \，m^2_a \，t} {16π} $。 （ALP）自我能源的紫外线差异需要有效动作中的高阶衍生术语。 We find that at high temperature, the finite temperature effective mass of the (ALP) is $m^2_a(T) = m^2_a(0)\Big[ 1-(T/T_c)^4\Big]$, with $T_c \propto \sqrt{m_a(0)/g}$, \emph{suggesting} the possibility of an inverted phase transition, which when combined with higher衍生物可能表明异国情调的新阶段。我们讨论了对结构形成，相对论物种的有效数量以及宇宙微波背景的双折射的可能后果。
We study the non-equilibrium dynamics of a pseudoscalar axion-like particle (ALP) weakly coupled to degrees of freedom in thermal equilibrium by obtaining its reduced density matrix. Its time evolution is determined by the in-in effective action which we obtain to leading order in the (ALP) coupling but to \emph{all orders} in the couplings of the bath to other fields within or beyond the standard model. The effective equation of motion for the (ALP) is a Langevin equation with noise and friction kernels obeying the fluctuation dissipation relation. A ``misaligned'' initial condition yields damped coherent oscillations, however, the (ALP) population increases towards thermalization with the bath. As a result, the energy density features a mixture of a cold component from misalignment and a hot component from thermalization with proportions that vary in time $(cold)\,e^{-Γt}+(hot)\,(1-e^{-Γt})$, providing a scenario wherein the ``warmth'' of the dark matter evolves in time from colder to hotter. As a specific example we consider the (ALP)-photon coupling $g a \vec{E}\cdot \vec{B}$ to lowest order, valid from recombination onwards. For $T \gg m_a$ the long-wavelength relaxation rate is substantially enhanced $Γ_T = \frac{g^2\,m^2_a\,T}{16π} $. The ultraviolet divergences of the (ALP) self-energy require higher order derivative terms in the effective action. We find that at high temperature, the finite temperature effective mass of the (ALP) is $m^2_a(T) = m^2_a(0)\Big[ 1-(T/T_c)^4\Big]$, with $T_c \propto \sqrt{m_a(0)/g}$, \emph{suggesting} the possibility of an inverted phase transition, which when combined with higher derivatives may possibly indicate exotic new phases. We discuss possible cosmological consequences on structure formation, the effective number of relativistic species and birefringence of the cosmic microwave background.
