31. In chemistry, perturbation theory was used to obtain the first solutions for the helium atom. 32. This means that one can manage this theory only by perturbation theory , with small nonlinearities. 33. See perturbation theory for more details. 34. Its validity however extends beyond the scope of perturbation theory as has been demonstrated by Molinari. 35. She has collaborated on perturbation theory . 36. Perturbation theory also fails to describe states that are not generated variational method and the WKB approximation.37. We will briefly examine the method behind Dirac's formulation of time-dependent perturbation theory . 38. Perturbation theory can be used in this regime to discuss the properties of weakly interacting electron systems.39. In ordinary QM these terms have to be put in by hand and treated using perturbation theory . 40. In the low energy limit of QCD, a description by means of perturbation theory is not possible.
