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seen Oct 26 '12 at 8:12

Jul
2
awarded  Curious
Nov
7
awarded  Popular Question
Dec
19
awarded  Nice Question
Dec
9
awarded  Teacher
Oct
19
comment Dilatations in non-relativistic QM and operator tranformation
Ok, I didn't think about this passage from active to passive transformations with dilations, seems a bit weird to "shrink" a system but clearly not enough to stop a theoretical description ;)
Oct
19
asked Dilatations in non-relativistic QM and operator tranformation
Oct
18
comment Non-commuting operators can't share any eigenvector
I think you got the point at the end (plus thanks for the numerical example). The context is about Bloch theorem and Bloch wave-functions, to describe for example electrons in a periodic static crystal.
Oct
18
comment Non-commuting operators can't share any eigenvector
Hum.. I'm not sure about your view on the problem, you're postulating from the beginning that $\alpha$ is not annihilated by the commutator, which is what I am questioning. Why should it annihilate every eigenvectors of $H$?
Oct
18
comment Non-commuting operators can't share any eigenvector
French QM textbook by Aslangul: amazon.fr/… The chapter on electrons in a crystal.
Oct
18
accepted Non-commuting operators can't share any eigenvector
Oct
18
asked Non-commuting operators can't share any eigenvector
Oct
10
accepted Path integral on matrix model
Oct
10
asked Path integral on matrix model
Oct
3
accepted Clarification on “central charge equals number of degrees of freedom”
Sep
30
asked Limit on space-time dimension from susy
Sep
28
accepted “low-energy effective action” but in what sense?
Sep
28
comment “low-energy effective action” but in what sense?
Thanks for the time you put in this detailed answer Lubos. I am familiar with the concept of renormalization group and effective field theory. My interrogation was about arguments specific to the derivation of this effective action, or differences between in an "effective field theory"-description in string theory in comparison to quantum field theory. But you answered that.
Sep
28
asked “low-energy effective action” but in what sense?
Sep
26
comment Clarification on “central charge equals number of degrees of freedom”
I already went through the light cone quantization of bosonic string theory, and the path integral formalism but the answer did not appear (clear) to me...
Sep
26
comment Clarification on “central charge equals number of degrees of freedom”
Thanks for both comments, I read the two question page you are referring to Qmechanic but I don't feel like it answers my question, maybe it wasn't clearly formulated. My point was only asking why those fields (b/c system) give a algebraically negative contribution to the "number of degrees of freedom of your theory"-number. Is it because in that case, the intuitive association central charge = number of dof is a bit abusive? Is it because the b/c are fictitious dof (accounting for a gauge symmetry)? Maybe something else?