New posts in Perturbation Theory

How to unify the cumulant expansion and Feynman diagram expansion?

Are the matrix elements of $S$-matrix Lorentz invariant?

What's the difference between perturbative QCD, non-perturbative QCD, and gauge theory QCD?

Struggling to understand degenerate perturbation theory

QFT perturbation theory

Drive frequency for second order quantum transitions

Can we get full non-perturbative information of interacting system by computing perturbation to all order?

One-loop Correction to Effective Action

Perturbation Theory and Thermodynamic Limit

Does QED really break down at the Landau pole?