Recent content by tupos

It can't be used for arbitrary coupling constant. But I can say the same for simple harmonic oscillator, as its energy becomes large as n is large, that is why there is no sense of trying find a correction for almost infinite value, moreover with that big n one can use quasi classical approach...

In this sense of course. But if you use operator method you can find the whole spectrum for anharmonic oscillator. But standard PT can't be used for any coupling constant. So it is incorrect to say that PT is not converge, because it can't be used. Anyway it is my own opinion. Regards.

Not correct. It happens because you take incorrect zero order wave functions, that is why your series doesn't converge for every alpha. However if you take correct zero order wave functions you will find complete spectrum. This is a similar to polaron problem. It was proved that you can't use...

I know very well what is internal electron line. I just wanted to point out your attention that internal electron line is not a real electron because for this virtual particle it is not necessary that p=-m^2, that's all.

Hello Hans, I didn't shout. Sorry if you get me wrong, I agree with you that there is no sense in space like and so on. But you wrote and I commented it that "An internal electron line originates from the original electron but has a changed momentum" you wrote it. I agree that nonsense is...

Nonsense. The definition of real electron p^2 = -m_{R}^2 where m_{R} is a real experimental mass. There is no evidence to conclude that p^2 is equal to m^2 for internal electron line. The same with photon, no evidence to say that k^2 = 0 for internal photon line. Regards.

I really can't understand sense of this discussion. Why does everybody separate electric and magnetic field? It is the same field! People here speak about electric field more only because of the relation E=cB that's all. There is no difference between "electric" and "magnetic" photons they...

Hello maverick, First of all you should forget about all notations that you wrote and think what you are doing step by step. I will explain you it now. What is the equation for S matrix in interaction picture i\frac{\partial S(t,t_0)}{\partial t} = H_{I}(t)S(t,t_0) what you want to do is to...

Hello, In your prevision question about density matrix I already answered how to do it. The definition of S matrix is \Phi(\infty) = (I+iT)\Phi(-\infty). \Phi(-\infty)\equiv v Now what is the problem? You know that \Phi^{*}_{\alpha}\Phi_{\beta} = \rho^{'}_{\alpha\beta} So you know the...

I guess it is translation to English. Originally Landau book in Russian also use Sp except Tr.

Sp = Tr, Sp from deutsch word spur = trace, I'm surprised that you have never seen this before. For example one of the most famous books on QM by Albert Messia, he uses Sp except Tr there.

Hello guys, It is quite understandable why you can write your final density matrix in this form \rho ^{'}= \frac{T\rhoT^{\dag}}{Tr[T\rhoT^{\dag}] The sense of your T operator is to "create" final states \Psi = T v. Lets say we have scattering of relativistic electrons in external field...

Hello guys, The problem with vanadium calculation is that he use asymptotic calculation of differential cross section. If you open any book on quantum mechanics, you'll find out the integral equation for scattering theory. it is a sum of plain wave and integral of...

I registered here only to tell that you guys wrong. It ca't be singularity simply from mathematical point of view. Your Coulomb wave functions are finite for any angle. But you have singular cross section. What is it? Then try to calculate total cross section or transport, which is extremely...