The basic algorithm of degenerate perturbation theory is quite simple:(adsbygoogle = window.adsbygoogle || []).push({});

1.Write the perturbed Hamiltonian as a matrix in the degenerate subspace.

2.Diagonalize it.

3.The eigenstates are the 'correct' states to which the system will go as the perturbation ->0.

But what to do if the first order does not break the degeneracy?

For instance, if the perturbation matrix elements are all 0 in the degenerate subspace.

It seems unlikely to me that there is nothing else to be done in that case....

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# Degenerate pertubation theory when the first order fails

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