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Results tagged with perturbation-theory
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user 72068
Perturbation theory refers to methods for understanding physical systems by treating them as small modifications to exactly solvable systems.
1
vote
About $\phi^4$ theory
Why in the interaction term of the hamiltonian operator do we encounter the free field?
Because we work in the Interaction picture. You stated this in your question, so I think you already know abou …
- 23.3k
2
votes
In degenerate perturbation theory why can we assume that matrix elements above and below the...
The picture shows some original Hamiltonian H which has some degeneracies. Suppose I have some perturbation V to the system and I want to find the new energies and eigenstates of the system.
...
My i …
- 23.3k
3
votes
Taking derivative with respect to quantum canonical ensemble expectation value
$$\partial_{x_b} \exp(-\beta H/N)\approx -\exp(-\beta H/N) (\frac{\beta}{N})(\partial_{x_b} H) $$
My question is, what is the strict justification for the last step? How to prove that the error incu …
- 23.3k
1
vote
Accepted
Stark Effect for the multiplet $n = 2$ (Gottfried, problem 12, chapter 5, 2nd ed.)
(a) Calculate the matrix elements of $eEz$ in the basis that diagonalizes $H_{fs}$. Show that
the $|m|= 3/2$ states are unaffected,
whereas the perturbed energies and eigenstates in the
space of th …
- 23.3k