New posts in Perturbation Theory

Why do the counterterms in renormalized $\phi^4$-theory with power two in fields give vertices and not propagators?

Quantum Field Theory in position space instead of momentum space?

Why does the branch cut of the self-energy begin at $2m$?

Use my example to explain why loop diagram will not occur in classical equation of motion?

Relativistic correction to Hydrogen atom - Perturbation theory

Can Feynman diagrams be used to represent any perturbation theory?

Perturbation theory for a particle in a weak potential

What are non-perturbative effects and how do we handle them?

Why are many physicists trying to develop non-perturbative quantum theories?

Why do we still use perturbation theory, when we have advanced numerical methods and fast computers?