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asked Non-Hermitian Lagrangian in Quantum Field Theory
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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
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asked A simple example of symmetry setting the properties of a Physical System
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Oct
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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?