标题： 关于从弦世界面推导Gibbons-Hawking-York项的评论 显示英文标题

标题： A Comment on Deriving the Gibbons-Hawking-York Term From the String Worldsheet

摘要： 在这篇短文中，我们证明了从整体非规范球面配分函数的非线性sigma模型世界面推导出的非协变度规边界项与Gamma-Gamma非协变作用中的爱因斯坦边界项密切相关。 事实上，当用外蕴曲率张量的迹来表示时，我们展示了这个边界项具有Gibbons-Hawking-York边界项一半的系数，从而使得总（体内部加上边界）非规范经典作用量在Dirichlet边界条件下具有适定的变分原理。 显示英文摘要

摘要： In this note, we show that the noncovariant metric boundary term obtained from the nonlinear sigma model worldsheet derivation of the bulk off-shell sphere partition function is closely related to the Einstein boundary term in the Gamma-Gamma noncovariant action. In fact, when expressed in terms of the trace of the extrinsic curvature tensor, we illustrate that this boundary term has one-half the coefficient of the Gibbons-Hawking-York boundary term required such that the total (bulk plus boundary) off-shell classical action has a well-posed variational principle with Dirichlet boundary conditions.