Recent content by Lucien1011

What do you mean by the word wavefunction? I guess you can always go to the classical limit, where you have classical fields for photons.

Hi all, I am studying QFT using John Preskill's notes. I have a question about the propagator and poles. On page 2.91, at the bottom, he said that there is a s-channel pole, which is the pole of the exact propagator. Then he claimed that by the argument about unitarity in page 2.70, the pole...

If you use the non-degenerate perturbation theory, it happens that the correction to wavefunction has undetermined coefficients. I guess maybe these coefficients are not physically important and hence can be arbitrarily chosen. What do you think?

Can I use these to say that we can use non-degenerate perturbation theory to calculate the new wavefunction

Oh you are only talking about the energy shift, I am so careless to take this important point. Sorry for that. I understand all you said now. Well my book is Quantum Mechanics by B.H.Bransden and C.J.Joachain(Second Edition). That part is CH12.1 "The Stark effect and the rigid rotator". Sorry...

Do you mean that since the perturbed wavefunction to the first order of \lambda is degenerate to m so that non-degenerate wavefunction can be applied? Why is it true? Can you explain a bit more? Thank you:smile:

Yeah I know if A,B commute and B,C commute doesn't mean A,C commute. Actually I just think of a good way to present my thought. Can you comment on this? So both unperturbed hamilotonian and perturbed one commute with Lz. Therefore, under both unperturbed and perturbed situations the energy and...

I can't quite understand the first paragraph. Can you explain it more? Yeah my thought is kind of related to the closeness you mentioned. Thanks for reminding me this. I feel I understand it more now.

Sorry for poor presentation The hamitonian of the system is \frac{L^2}{2m} - kBz and the unperturbed eigenfunction is Y_{l,m}(\theta,\phi) As you know, the unperturbed eigenfunction is degenerate with respect to m (where m =-l,-l+1,...,l ). But the book said we can use non-degenerate...

Consider a system of a rigid rotator together with a uniform E-field directing along z-axis. So to calculate the perturbed energy and wavefunction we have to use perturbation theory. But the book said we can use non-degenerate one to calculate the result. I wonder why. It is because the original...

So what is the definition of affine connection? Am I correct to say that to define the parallel displacement such that the vector displaced does not change in magnitude and direction, we have to define F=g[ij,k] (ignore the superscript and subscript) as our affine connection? where [ij,k]is the...

In covariant derivative, we have a quantity called affinity. The book says: When defining an affine connection, a coordinate frame must first be selected and the choice of the components of the affinity is then arbitrary within this frame. However, when these are all determined, the component...

Sorry I mix up H and B too. I haven't turn to Electromagnetism for some time so I forget many things. Actually I mean H is proportional to M. What makes the Magnetic susceptibility a constant? I interpret it like this. I never think that H is REALLY proportional to M. In Griffiths' Book, it is...

Can anyone tell if I am correct or not. I am really not sure. First by v2f - v1f = e(v1i - v2i) and conservation of momentum, v1f and v2f is known. then by conservation of angular momentum (axis taken at the cg of the rod), the angular velocity of the rod is known. And that does it.

Sometimes I think it is useful to think of mv2/2 for each point first.