Recent content by Mesmerized

thanks, that's right

what kind of trouble? I thought there should be no problem in passing from QED to limit where fermion mass is 0

Thanks for the reply andrien, I understand your point. But my question is a little different. When you draw the diagrams corresponding to fermion propagator corrections, the propagator itself becomes an infinite sum (like in formula 7.22 in Peskin's book), which in effects takes the propagator...

Hello, in QED the corrections to electron propagator change the bare electron mass from m_0 to m=m_0+δm=m_0+∑({\not}p=m) (Peskin, formula 7.27). This is the consequence of the result, that the propagator changes from i/({\not}p-m_0) to i/({\not}p-m_0-∑({\not}p))). This part is written very...

hi dex, thanks for the hint, I will check.

thanks for the answers. Sam, this is what I understood from your responses in those threads. (1/2,1/2) is a representation with two indices (dotted and undotted), and each of those two 1/2 representations acts on the corresponding index. I understand this part. Then, as you write, "It (the...

Hello, I'm reading Zee's book 'Quantum Field Theory in a Nutshell', the chapter about Lorentz group representations at the moment. In the end of the chapter there is suggested an exercise - "Show by explicit computation that (1/2,1/2) is indeed the Lorentz vector". And I just can't figure it...

thanks. thanks Bil_K, it seems there is an explanation of that in your link, I will once watch into it more carefully

What it means "the theory violates unitarity" Hello, I know what unitary transformation is, but what does it mean that the theory does or does not violate unitarity? For example in some textbooks on QFT one can read that the Fermi theory of beta decay, which is not renormalizable, also violates...

thanks for the answers. thank you Rap, that explains it clearly

Hello, Here http://www.mathpages.com/home/kmath210/kmath210.htm it is written that "...in order to actually convey information, a signal cannot be a simple periodic wave...". I've met this statement in several other places too, this one is just for reference. What does that mean that a simple...

thank you for such a detailed answer.

Hello, I'm reading Weinberg's vol.1 on Quantum Theory of Fields and stuck on the following problem. In the massless case Wigner's little group is the group of Lorentz transformations that keep the vector (0,0,1,1) invariant. (I'm going with Wigner's notations, where the vector is denoted...

thanks, Muphrid, but I guess you're a little too clever for me for now. We'll talk after some half a year :) And that matrix from Weinberg's book I was talking about, it turned out that it was written really wrong, but in the russian version, which I'm reading. In the original it's perfectly...

How? It is symmetric. Just put it in a matrix form I'm trying to understand what you have written here, and it seems like you've found one particular example of Lorentz transformation, which is orthogonal, but in general it isn't I think