标题： 量子场非微扰动力学的控制研究远离平衡态 显示英文标题

标题： Controlled nonperturbative dynamics of quantum fields out of equilibrium

摘要： 我们从O(N)对称标量量子场论的2PI有效作用量的系统1/N展开中计算非平衡实时演化到次领头阶，这包括散射和记忆效应。 与标准1PI有效作用量的1/N展开相反，在可能存在复合算符期望值的情况下，次领头阶展开导致一个时间演化的有界过程，其中截断误差可以通过1/N的高次幂来控制。 我们详细比较了领先阶的结果，并确定了标准平均场类型近似的适用范围。 我们研究了“淬火”和“海啸”初始条件，这些条件常用于模拟重离子碰撞背景下理想化的远离平衡的介子动力学。 对于空间均匀的初始条件，我们发现三个典型的区域，其特征是早期时间的指数衰减，中间时间的参数上缓慢（幂律）行为，以及晚期时间向热平衡的指数趋近。 不同的时间尺度是从1+1维的时间反演不变方程的数值解中获得的，无需进一步的近似。 我们详细讨论了非平凡n点关联函数的非平衡行为，以及粒子数分布和逆斜率参数的演化。 显示英文摘要

摘要： We compute the nonequilibrium real-time evolution of an O(N)-symmetric scalar quantum field theory from a systematic 1/N expansion of the 2PI effective action to next-to-leading order, which includes scattering and memory effects. In contrast to the standard 1/N expansion of the 1PI effective action, the next-to-leading order expansion in presence of a possible expectation value for the composite operator leads to a bounded time evolution where the truncation error may be controlled by higher powers in 1/N. We present a detailed comparison with the leading-order results and determine the range of validity of standard mean field type approximations. We investigate ``quench'' and ``tsunami'' initial conditions frequently used to mimic idealized far-from-equilibrium pion dynamics in the context of heavy-ion collisions. For spatially homogeneous initial conditions we find three generic regimes, characterized by an early-time exponential damping, a parametrically slow (power-law) behavior at intermediate times, and a late-time exponential approach to thermal equilibrium. The different time scales are obtained from a numerical solution of the time-reversal invariant equations in 1+1 dimensions without further approximations. We discuss in detail the out-of-equilibrium behavior of the nontrivial n-point correlation functions as well as the evolution of a particle number distribution and inverse slope parameter.