碰撞强场QED动力学方程的第一性原理
Collisional strong-field QED kinetic equations from first principles
摘要：
从封闭时间路径上的非平衡量子场论出发，利用规范耦合$e$的系统展开，导出了强场量子电动力学（QED）的动力学方程。强场状态的特征在于$\mathcal{O}(1/e)$级的大光子场，其与例如以下的描述相关：强激光场、偏离中心的重离子碰撞的初始阶段和具有净费米子数的凝聚态系统。强场通过量子Vlasov和碰撞项进入动力学方程，我们推导出$\mathcal{O}(e^2)$阶。动力学方程的特点广义散射振幅，有自己的运动方程的费米子谱函数。描述包括单光子发射，电子-正电子对光生，真空（Schwinger）对生产，其逆过程，介质效应和贡献的领域，这是不限于所谓的局部常数交叉场近似。这推广了强激光场的强场QED中常用的动力学方程。特别是，我们推导出一个表达式的渐近费米子对数，包括领导级碰撞，并保持有效的强非均匀场。为了分析突出的限制情况下，我们还考虑平面波场，它是如何恢复毛茸茸的图片散射振幅进一步假设可以忽略不计的职业。已知的壳层上的描述恢复的情况下，简单地达到峰值的超相对论费米子职业。从强场的初始条件出发，碰撞强场方程是描述热平衡动力学的必要条件。
英文摘要：
Starting from nonequilibrium quantum field theory on a closed time path, we derive kinetic equations for the strong-field regime of quantum electrodynamics (QED) using a systematic expansion in the gauge coupling $e$. The strong field regime is characterized by a large photon field of order $\mathcal{O}(1/e)$, which is relevant for the description of, e.g., intense laser fields, the initial stages of off-central heavy ion collisions, and condensed matter systems with net fermion number. The strong field enters the dynamical equations via both quantum Vlasov and collision terms, which we derive to order $\mathcal{O}(e^2)$. The kinetic equations feature generalized scattering amplitudes that have their own equation of motion in terms of the fermion spectral function. The description includes single photon emission, electron-positron pair photoproduction, vacuum (Schwinger) pair production, their inverse processes, medium effects and contributions from the field, which are not restricted to the so-called locally-constant crossed field approximation. This extends known kinetic equations commonly used in strong-field QED of intense laser fields. In particular, we derive an expression for the asymptotic fermion pair number that includes leading-order collisions and remains valid for strongly inhomogeneous fields. For the purpose of analytically highlighting limiting cases, we also consider plane-wave fields for which it is shown how to recover Furry-picture scattering amplitudes by further assuming negligible occupations. Known on-shell descriptions are recovered in the case of simply peaked ultrarelativistic fermion occupations. Collisional strong-field equations are necessary to describe the dynamics to thermal equilibrium starting from strong-field initial conditions.
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