Recent content by PJK

Hey, the coupling constant in QFT is scale dependent. This scale \mu, it seems to me, is a mathematical tool used to regularize the infinities that arise at the loop level. Thus physical quantities have to be independent of this scale \mu. This implies that the coupling 'constant' is a...

Hey Physics Monkey, ok I think I understand what you mean: \phi \approx b + c^\dag So it destroys phi particles and creates phi antiparticles \phi^\dag \approx b^\dag + c^ So it destroys phi antiparticles and creates phi particles Thus in a process phi -> phi where the momenta k_i of the...

Thanks for your answer Physics Monkey! This is what I originally did, but I do not understand why the overlap with the two-particle states vanishes?

Somehow I have problems with figuring out the following problem: I know that the scalar field is obeying the follwoing equations: <0|\phi(x)|k> = e^{ikx} <0|\phi(x)^\dag|k> = 0 <k'|\phi(x)^\dag|0> = e^{-ik'x} <k'|\phi(x)|0> = 0 And I was told that I can deduce the following result from the...

Hi all, I want to calculate traces of Dirac matrices with a program like Mathematica. I found the package FeynCalc but it seems to be outdated. It is always producing results like this: 4 (-(DiracCanonical->False) (Factoring->False) (FeynCalcInternal->True) g^(mu nu)...

Hi! I have one more question: I do not understand at all how one gets eq 29.11 and (maybe) connected with this how Srednicki gets eq. 29.13... I would expect that the O-Operators also include the fields of higher momenta. Where does the propagator for the higher momenta fields come from? Sorry...

Thank you so much RedX! I really understood this now! Wow!

Ok I think I got that...so the bare parameters are 'infinite constants' and our ignorance is that we do not know there exact (infinite) value? Well I understand your argumentation but I do not see why the LSZ formula requires that the residue of the propagator is one. All I can see is that...

Hi all, I have posted this question as a separate thread in the forum originally but I think this is the better place for it: I have two questions regarding chapter 27 and 28 in Srednicki's book. On page 163 he states: "furthermore, the residue of the pole is no longer one. Let us call the...

Thank you very much! Sometimes I wished Srednicki would include one or two more sentences in his argumentation...

hi all, i have a question regarding page 81 in Srednicki's QFT book. He states there that the sum over all connected diagrams with a single source is zero. Then he says that if you replace this single source by an arbitrary subdiagram the sum will still be zero. Can somebody explain why this...

I have a question about an equation in Maggiore's Modern Introd. to Quantum Field Theory p.52: \delta x^\mu = w^\mu_\nu x^\mu = \sum_{\rho < \sigma} A^\mu_{(\rho \sigma)} w^{\rho \sigma} where the A is defined as A^\mu_{(\rho \sigma)}=\delta^{\mu}_{\rho}x_\sigma - \delta^\mu_\sigma x_\rho...

Ok I got it. Thank you! What I find very strange though is that he converts \sum_{n_i} \frac{1}{n_i!}V_i^{n_i} into exp(V_i) - I mean for example n_1 can be an arbitrary number e.g. 999888 and not 1. This doesn't look like an exponential series to me. Thank you for your answer.

Hi all, I have a question regarding p.97 of Peskin Schroeder and its explantion of disconnected diagram exponentation. I do understand the formula on the buttom of page 96. \prod{\frac{1}{n_i!}V_{i}^{n_i}} \cdot (value \; of\; connected \; piece) ButI do not understand the sum over \{ n_i \}...