Correlation Functions and Diagrams
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چکیده
The path integral gives us the time evolution operator, which in principle contains all the information about the dynamics of the system. However, in order to use the path integral to do physics we need to find a way to describe initial and final particle states in path integral language. The way to do this is to couple the fields to spacetimedependent background fields (“sources”) that can create or destroy particles. For example, in our scalar field theory, we add a source field J(x) coupled linearly to φ:
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