标题： 关于一维弦理论中的时变背景 显示英文标题

标题： On Time-Dependent Backgrounds In 1+1 Dimensional String Theory

摘要： 在微扰弦理论中，人们通常关注渐近可观测量，例如平坦时空中的S矩阵以及反德西特时空中的边界关联函数。 然而，存在一些背景，在这些背景下这类可观测量不存在。 我们研究了1+1维弦理论中此类背景的例子。 在这些例子中，李奥维尔壁会加速，并可能在过去和/或未来成为类空的。 当这种情况发生时，标准散射态所定义的相应零无穷远被李奥维尔壁屏蔽。 我们在参数空间中壁仍为类时的区域计算这些背景下的散射和粒子产生幅度，并讨论这种图像延续到类空区域的情况。 我们还从具有时间依赖费米面的背景中自由费米子动力学的角度讨论了物理现象。 显示英文摘要

摘要： In perturbative string theory, one is generally interested in asymptotic observables, such as the S-matrix in flat spacetime, and boundary correlation functions in anti-de Sitter spacetime. However, there are backgrounds in which such observables do not exist. We study examples of such backgrounds in 1+1 dimensional string theory. In these examples, the Liouville wall accelerates and can become spacelike in the past and/or future. When that happens, the corresponding null infinity, at which the standard scattering states are defined, is shielded by the Liouville wall. We compute scattering and particle production amplitudes in these backgrounds in the region in parameter space where the wall remains timelike, and discuss the continuation of this picture to the spacelike regime. We also discuss the physics from the point of view of the dynamics of free fermions in backgrounds with a time-dependent Fermi surface.