Hot answers tagged

3

Let's think about a system that has a two-fold degeneracy for some given energy level. That is, two states $ \psi_{a} $ and $ \psi_{b} $, both of which correspond to energy $ E_{0} $. An example would be a spin-1/2 particle with a Hamiltonian that is spin-independent. Now imagine that when we apply a perturbation, H', to the system, the degeneracy breaks ...


1

Of course in the spectrum of QED there is hydrogen atom. The problem is what to compute in the case of bound states and how to compute. The usual approach to a general QFT is perturbative, meaning that you start from free fields (in this case electron and photon) and then you think the compulg coupling between these fields (in this case $\bar\psi ...



Only top voted, non community-wiki answers of a minimum length are eligible