you need to understand perturbation theory in the context of qft. that's no small feat but since it's a pretty universally studied grad core subject there's a l

you need to understand perturbation theory in the context of qft. that's no small feat but since it's a pretty universally studied grad core subject there's a lot of material. this book was actually suggested to me here https://www.amazon.com/Renormalization-Methods-William-David-McComb/dp/0199236526 https://www.amazon.com/Renormalization-Methods-William-David... two good (Gentle) senior undergrad books are https://www.amazon.com/Student-Friendly-Quantum-Field-Theory/dp/0984513957 https://www.amazon.com/Student-Friendly-Quantum-Field-Theory... https://www.amazon.com/Field-Quantization-Walter-Greiner/dp/3540780483 https://www.amazon.com/Field-Quantization-Walter-Greiner/dp/... and then there's always griffiths https://www.amazon.com/Introduction-Elementary-Particles-David-Griffiths/dp/3527406018 https://www.amazon.com/Introduction-Elementary-Particles-Dav... note that you don't need to read this cover to cover if you're not interested in actually doing calculations. you can skim.