String Sandwiches and Worldsheet Quantum Equivalence Principle

This lecture explores the Worldsheet Quantum Equivalence Principle (WQEP) in string theory, focusing on how it can be made explicit through Sandwich Virasoro Constraints (SVC). Learn how solutions to SVC fall into four distinct classes based on whether they preserve or break worldsheet parity P and/or time reversal T. Discover the connection between the standard Minkowski worldsheet observer described in string theory textbooks and the class that maintains both P and T symmetries. Examine the three other solution classes representing Hilbert spaces of non-inertial worldsheet observers where P, T, or both symmetries are broken. The presentation also introduces applications to accelerated worldsheets with horizons, establishing foundations for thermal string theory and the study of strings probing black hole horizons.