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Feb
5
awarded  Popular Question
Jan
17
awarded  Notable Question
Jan
17
awarded  Popular Question
Jan
13
revised What are anomalous threshold singularities
deleted 2 characters in body
Jan
13
answered What are anomalous threshold singularities
Jan
9
awarded  Nice Answer
Dec
16
comment Proof of Yang's theorem
@LubošMotl that's true. But I must be blind; which amplitude do you refer to that is bilinear in epsilon-V?
Dec
14
awarded  Popular Question
Dec
11
comment Different Signs in Yang Mills Gauge Transformations
In the end, I found out that this discrepancy amounts to a change of sign in the gauge coupling constant, or in the sign of the vector potential. It doesn't affect final results for computations of physical quantities.
Oct
2
accepted What is the chemical symbol for Mu-mesic atoms?
Sep
11
awarded  Nice Question
Aug
24
awarded  Revival
Aug
15
comment What are Maximally Helicity Violating (MHV) Amplitudes?
Neat. What is it that makes all amplitudes with all helicities the same sign (or with just one opposite sign) vanish?
Jul
28
comment How is intensity defined for quantized EM fields?
I think the Intensity becomes an operator which has a form very similar to the electromagnetic Hamiltonian (i.e. with $|E^2|$)
Jul
10
awarded  Yearling
May
13
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Mar
26
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Mar
13
comment Do the norms of the total and the orbital angular momentums commute? If yes, why is there a problem with 2p_{1/2}?
Of course they do commute. The problem is that $\vec{L}^2$ and $\vec{S}^2$ may not commute with the Hamiltonian $H$. If the fine structure splitting of the hydrogen atom is treated exactly by the methods of relativistic quantum theory, the solutions are superpositions of states of orbital angular momenta ($\ell = 0, 2, 4, ...$ or $\ell = 1, 3, 5, ...$), because the relativistic Hamiltonian does not commute with $\vec{L}^2$.
Feb
16
comment Do Standard Model Yukawa couplings depend on the gauge choice?
@Shep Yes, you can think of it that way. Otherwise you have to do a little more work to identify the conserved charge, and identify that as $Q_\text{new}$.
Feb
15
comment Do Standard Model Yukawa couplings depend on the gauge choice?
@Shep Srednicki assigns the Higgs a hypercharge of $Y=-1/2$ (which is opposite from most everyone else's definition). As a result, Srednicki's Higgs field is rotated by $\pi/2$ around the isospin-$y$ axis, followed by $C$-conjugation with respect to everyone else Higgs's field [analog of the $G$-parity in hadron physics].