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seen Jun 25 at 17:58

Oct
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awarded  Popular Question
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awarded  Curious
Jun
17
asked Is the total cross section a Lorentz Invariant?
Jan
21
awarded  Yearling
Oct
18
answered Is Higgs mechanism necessary in QCD?
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Apr
3
comment A simple example of symmetry setting the properties of a Physical System
Angular momentum is a good one, but it would be nice to find a more "down to Earth" example (sorry for the pun). Does a spinning top needs to be invariant under any rotation? Or does less symmetric top works? (say invariant under 90 degree rotations - with a square cross section). This looks promissing, I'm trying to understand it: en.wikipedia.org/wiki/Rattleback
Apr
2
asked A simple example of symmetry setting the properties of a Physical System
Jan
21
awarded  Yearling
Oct
7
comment How can perturbativity survive renormalization?
But, being more specific: when you do perturbation you have to expand $Exp(- i S_{I}- i S_{CT})$ (S are the action of the interaction and of the counterterms), and pick the first terms. I understand doing that for $S_{I}$ but not $S_{CT}$. It seems that this step in the calculation is invalid. Of course the infinities will cancel but that seems to me like "holding" a limit - it seems like the order in which you take limits ($\lambda$ small vs. huge regulator) make a difference in the result
Oct
7
comment How can perturbativity survive renormalization?
The question is more specific than "explain me renormalization". Also, if the infinity is just "pushed to the next order", how can you explain truncating the series?
Oct
6
asked How can perturbativity survive renormalization?
Sep
3
comment Ward Takahashi identities from Z invariance
Just be sure: so I'm right about this commutation business being all wrong? Also: is the link I posted to the book itself (on Google books) working?
Sep
2
revised Ward Takahashi identities from Z invariance
added 130 characters in body
Sep
2
accepted What´s the importance of the normalization of the Kinetic term?
Sep
2
comment What´s the importance of the normalization of the Kinetic term?
Thanks, I'll have to check that keeping $\hbar$ around. I included some comments in the question.