标题： 有效拉格朗日中的微扰计算和 $2D$ 闭弦场论 显示英文标题

标题： Perturbative Calculations in the Effective Lagrangian and $2D$ Closed String Field Theory

摘要： 本文致力于研究二维闭弦场论。 我们比较了两种不同的方法：BRST闭弦场论和弦的有效拉格朗日。 我们证明了二次作用量和树级散射振幅的极点结构是一致的。 我们研究了各种规范固定程序的优点和缺点。 特别是，我们在有效拉格朗日的背景下讨论共形规范，并在一般的BRST方法中讨论Siegel规范和类似于Lorentz的规范。 我们讨论了离散态如何通过直接求解运动方程以及通过分析散射振幅的极点结构在特定规范固定下存活的方式。 显示英文摘要

摘要： This paper is devoted to the study of closed string field theory in two dimensions. We compare two different approaches: BRST closed string field theory and the string effective Lagrangian. We show that the quadratic action and the pole structures of tree-level scattering amplitudes agree. We study merits and drawbacks of various gauge fixing procedures. In particular, we discuss conformal gauge in the context of the effective Lagrangian, and Siegel and Lorentz-like gauge in the general BRST approach. We discuss the ways in which discrete states survive a particular gauge fixing both by directly solving the equations of motion, and by analyzing pole structure of the scattering amplitudes.