# Degenerate perturbation theory question

1. Mar 28, 2007

### gulsen

This's a question from Griffiths, about degenerate pertrubation theory:

For $$\alpha=0, \beta=1$$ for instance, eq. 6.23 doesn't tell anything at all!

What does it mean "determined up to normalization"?. Equations 6.21 and 6.23 involve 3 unknowns ($$\alpha, \beta, E^1$$), and Griffiths solved them for $$E^1$$ in terms of Ws, eliminating $$\alpha, \beta$$. Any ideas about solving the question?

I'm stuck.

(note: this's not a homework!)

Last edited: Mar 28, 2007
2. Mar 29, 2007

### nrqed

Of course it tells us something, it tells us that one of the first order correction to the energy is simply $W_{bb}$!!!
It's not clear what is the "question" you have in mind. But if you simply isolate, say, beta from one of the two equations, plug in the other equation, you will see that alpha will drop out completely. Then you will have a quadratic equation for E_1 and you get the two roots Griffiths gives. That's all there is to it. What is the difficulty you are having?

(aside: it's even miore clean to realize that the two equations can be put in matrix form so that E_1 is really the eigenvalue of the "W matrix")

3. Apr 3, 2007

### gulsen

Eh ^-^' I mean, it doesn't tell anything about $\alpha$

I was trying to ask how I would get $\alpha$ and $\beta$. And secondly, how to solve the question (all seem "obvious", but how do I show them explicitly?).

Maybe I should add that I'm a complete newbie to the subject (perturbation)!