because that's how they are used in scattering calculations.spaghetti3451 said:1. Why are the external lines on an one-particle irreducible diagram truncated/amputated?
One also defines ##k##-particle irreducible diagrams (which cannot be made disconnected by removing up to ##k## internal lines). These describe the properties of ##k##-point correlations (involving ##k## particles, hence the name), which are important for calculations in nonequilibrium quantum field theory.spaghetti3451 said:2. What is the motivation for the word 'one-particle' in the terminology?
The terminology of 1PI diagrams is used in theoretical physics to describe and analyze the interactions and scattering processes of particles. It helps to simplify and visualize complex calculations related to quantum field theories.
"1PI" stands for "one-particle-irreducible", which refers to the property that these diagrams cannot be broken down into smaller diagrams without cutting through a propagator line.
1PI diagrams are a subset of Feynman diagrams that only include diagrams with no external legs, representing purely quantum fluctuations. They are often used in conjunction with Feynman diagrams to calculate scattering amplitudes in quantum field theory.
No, 1PI diagrams are primarily used in particle physics and quantum field theory calculations. They are not applicable to classical physics or systems with non-perturbative interactions.
One limitation of 1PI diagrams is that they only consider the interactions of single particles, neglecting the effects of higher-order particle interactions. Additionally, their calculations can become very complex and difficult to interpret in systems with a large number of particles or interactions.