Recent content by cedricyu803

Oh right! Thanks!

Hi, In (1+1)D Minkowski spacetime, with coordinates (t,x), let's say there is an incoming plane wave of frequency \omega, \phi_{in}(t,x)=e^{-i\omega (t+x)}. There is a mirror, x=z(t) It reflects the incoming plane wave and emits an outgoing plane wave. Question: why is the outgoing wave...

Followup question: I am struggling to move from eq. 93.16 to 93.17. Now that n=\frac{1}{16 \pi^2} \int d^4x Tr(F_{\mu \nu}\tilde{F}^{\mu \nu}) =\frac{1}{16 \pi^2} \int d^4x \partial _\mu Tr(\epsilon^{\mu \nu \sigma \tau} (A_\nu F_{\sigma \tau}+\frac{2i}{3} A_\nu A_\sigma A_\tau)) \equiv...

Ahh right, now I got it. Thanks a lot

Hi, I am going through the derivation of an instanton solution (n=1) in Srednicki Chp. 93. Specifically, I went through eqn.s 93.29-93.38. However the sign of the Levi-Civita Symbol is bugging me: It says that in 4D Euclidean space, \epsilon^{1234}=+1 in Cartesian coordinates implies...

Thanks for your reply. I understand what Srednicki meant. And my understanding is that gauging the U(1) makes the global EM U(1) current always conserved. What I wanted to show explicitly is $$\partial _\mu j^\mu=0$$ for the EM current (global U(1)) So I will need to make use of...

Hi I am re-reading Srednicki's QFT. In chapter 58, he points out that the Noether current $$ j^\mu=e\bar{\Psi}\gamma^\mu\Psi$$ is only conserved when the fields are stationary, which is obvious from the derivation of the conservation law. Meanwhile he assumes that $$\partial _\mu...

Thanks very much for your recommendation. I will look for this book in a public library. I am lucky to have been recommended Srednicki's book by my prof as well, after I told him I was having a hard time Peskin & Schroeder. Hopefully I can finish the whole book by the end of this semester...

Oh right. I wasn't aware of the difference between the operator and the matrix. So the charge conjugation of \beta does nothing to it. That's why I got a minus sign. Thanks very much!

Homework Statement I am reading Srednicki's QFT up to CPT symmetries of Spinors In eq. 40.42 of http://web.physics.ucsb.edu/~mark/ms-qft-DRAFT.pdf I attempted to get the 2nd equation: C^{-1}\bar{\Psi}C=\Psi^{T}C from the first one: C^{-1}\Psi C=\bar{\Psi}^{T}C Homework Equations...

1. OK now k in a(k) is the operator in the Schrödinger Picture In \varphi^+ (x)=e^{iH_{0}t}\varphi^+ (\mathbf{x},0)e^{-iH_{0}t}=\int \widetilde{dk}e^{ikx}a(\mathbf{k}) follows from [a(\mathbf{k}),H_{0}]=\omega a(\mathbf{k}), so e^{iH_{0}t}a(\mathbf{k})e^{-iH_{0}t} is the Heisenberg picture...

Hi folks, originally I read Peskin & Schroeder but then I realized it was too concise for me. So I switched to Srednicki and am reading up to Chapter 5. (referring to the textbook online edition on Srednicki's website) Two questions: 1. In the free real scalar field theory, the creation...

Like you, I am studying at one of the two good universities in physics in Hong Kong. Which field are you interested in? From my observation, there are 2 or 3 professors in my university (guess which) got their PhDs in HK on material science/ solid state physics... then got postdoc positions in...

Homework Statement [Math. for Physicists, M. Stone Problem 1.4] Assume that a rod of length L is only slightly bent into the yz plane and lies close to the z axis, show that the elastic energy can be approximated as U[y]= \int_{0}^{L} \frac{1}{2}YI(y'')^2 dz Homework Equations It is...

First thanks to Sentin3l for providing a nice website for me to look at. For dreamLord's comment, I think following the European system we take the same advanced ug math and phys courses like US students do. The transcript will tell. The only disadvantageous is that we have one less year to...