标题： 经典和量子多体描述密集物质中的轫致辐射（兰道-波梅兰丘克-米格达尔效应） 显示英文标题

标题： Classical and quantum many-body description of bremsstrahlung in dense matter (Landau - Pomeranchuk - Migdal effect)

摘要： 关于非平衡致密物质中轫致辐射过程中相干效应重要性的几点考虑（兰道-波梅兰丘克-米格达尔效应）被提出。它们对于高能核碰撞中的光子和双轻子产生、QCD输运中的胶子辐射或部分子动力学以及超新星爆炸和热中子星中的中微子和轴子辐射的应用具有特别的相关性。讨论了由经典输运模型描述的源的轫致辐射的软行为，并提出了用于物质中辐射截面的口袋修正公式，这些公式以标准输运系数的形式表示。在非平衡量子场论（施温格-卡丹诺夫-拜姆-凯尔迪什）框架下也讨论了辐射率。提出了一种按物理上有意义的术语对图进行分类并相应地重求和的方法，该方法考虑了物质中所有源粒子的有限阻尼宽度。这样，该展开中的每个图都已经摆脱了红外发散。从这组图中恢复了正确的准粒子和准经典极限。给出了热平衡致密物质的显式结果。图示描述可能暗示了一种包括非平衡致密物质中离壳粒子传播的输运理论的表述。 显示英文摘要

摘要： Some considerations about the importance of coherence effects for bremsstrahlung processes in non--equilibrium dense matter (Landau - Pomeranchuk - Migdal - effect) are presented. They are of particular relevance for the application to photon - and di-lepton production from high energy nuclear collisions, to gluon radiation in QCD transport, or parton kinetics and to neutrino and axion radiation from supernova explosion and from hot neutron stars. The soft behavior of the bremsstrahlung from a source described by classical transport models is discussed and pocket correction formulas for the in-matter radiation cross sections are suggested in terms of standard transport coefficients. The radiation rates are also discussed within a non--equilibrium quantum field theory (Schwinger - Kadanoff - Baym - Keldysh) formulation. A classification of diagrams and corresponding resummation in physically meaningful terms is proposed, which considers the finite damping width of all source particles in matter. This way each diagram in this expansion is already free from the infra--red divergences. Both, the correct quasi--particle and quasi--classical limits are recovered from this subset of graphs. Explicit results are given for dense matter in thermal equilibrium. The diagrammatic description may suggest a formulation of a transport theory that includes the propagation of off--shell particles in non--equilibrium dense matter.