Perturbative Expansion in the \( \phi ^4_4\) Model
Problems with an exact construction of the quantum \(\phi ^4_4\) model. The interaction picture. The Gell-Mann–Low formula for Greeen’s functions. The generating functional for Green’s functions. The exponential Wick formula. The Feynman free propagator. Regularized Feynman diagrams in four-momentum space. Normal ordered interactions. Cancelation of vacuum bubbles.