热介质中的实时和非实时$Q\bar{Q}$关联函数
Real and imaginary-time $Q\bar{Q}$ correlators in a thermal medium
摘要：
研究了一对重费米子（记作$Q$和$\bar{Q}$）在热/稠密介质中的行为.虽然我们考虑的是$Q$和$\bar{Q}$表示重夸克的情况，但我们的处理将限于简化模型，它与QCD只有一些一般的相似之处。我们研究特别是重费米子的质量是无限的极限情况。这样就可以精确地推导出许多结果：可以为重夸克的相关子建立一个薛定谔方程;相互作用效应取指数，从而为这个薛定谔方程导出一个简单的瞬时有效势。我们考虑简单的模型中的$Q\bar Q$对传播的介质。在介质是光子和轻带电费米子的等离子体的情况下，虚部在该有效势中发展。我们讨论的物理解释，这个虚部的重粒子和轻费米子的介质之间的碰撞;相同的碰撞也决定了重费米子的阻尼率。最后，我们研究了重费米子对的实时传播子与其对应的欧几里德传播子之间的联系，并证明了进入实时传播子的薛定谔方程的势的实部是用实时形式计算的自由能.
英文摘要：
We investigate the behavior of a pair of heavy fermions, denoted by $Q$ and $\bar{Q}$, in a hot/dense medium. Although we have in mind the situation where $Q$ and $\bar{Q}$ denote heavy quarks, our treatment will be limited to simplified models, which bear only some general similarities with QCD. We study in particular the limiting case where the mass of the heavy fermions is infinite. Then a number of results can be derived exactly: a Schrödinger equation can be established for the correlator of the heavy quarks; the interaction effects exponentiate, leading to a simple instantaneous effective potential for this Schrödinger equation. We consider simple models for the medium in which the $Q\bar Q$ pair propagates. In the case where the medium is a plasma of photons and light charged fermions, an imaginary part develops in this effective potential. We discuss the physical interpretation of this imaginary part in terms of the collisions between the heavy particles and the light fermions of the medium; the same collisions also determine the damping rate of the heavy fermions. Finally we study the connection between the real-time propagator of the heavy fermion pair and its Euclidean counterpart, and show that the real part of the potential entering the Schrödinger equation for the real-time propagator is the free energy calculated in the imaginary-time formalism.
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