Don't have Telegram yet? Try it now!
http://peeterjoot.com/2018/10/29/phy2403h-quantum-field-theory-lecture-14-time-evolution-hamiltonian-perturbation-ground-state-taught-by-prof-erich-poppitz/
PHY2403H Quantum Field Theory. Lecture 14: Time evolution, Hamiltonian perturbation, ground state. Taught by Prof. Erich Poppitz