Cambridge University Press eBooks

The Contour Idea for Time-Dependent Averages: Forward and Backward Branches

Giancarlo Calvanese Strinati

Published Feb 6, 2026• 0 citations

Abstract

This chapter introduces the contour Schwinger–Keldysh method for time-dependent averages, in light of its relevance to nonequilibrium processes. A key feature of this approach is that it leaves open the possibility that no state of a system in the future can be identified with any of its states in the past. This method is here illustrated in detail with reference to time-dependent quantum averages, whereby for definiteness the system is initially prepared at the reference time t ₀ in a definite quantum state.

DOI: 10.1017/9781009411509.007

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