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May
14
answered If a symmetry operator S in a QFT annihilates the vacuum, why does S preserve the space of 1-particle states?
May
5
comment The $U(1)$ charge of a representation
@JakobH The generator of the U(1) charge $Y_{\gamma}$ needs by definition to commute with all root generators $E_{\gamma}$ of the unremoved nodes. The Cartan-Weyl generator $H_i$ corresponding to the removed node does not possess this property, but its dual (called a coweight) does. The duality transformation can be accomplished on weight space by means of the metric tensor.
May
5
awarded  Nice Answer
Mar
11
awarded  Revival
Mar
6
awarded  Enlightened
Mar
6
awarded  Nice Answer
Mar
6
revised The Aharonov-Bohm effect is purely classical, right?
deleted 4 characters in body
Mar
5
comment The Aharonov-Bohm effect is purely classical, right?
@levitopher you can obtain the semiclassical aproximation (including the A-B effect) from the path integral, but Tuyman's theory requires even less structure than needed for the path integral. He does not require the symplectic form to be integral, thus does not impose the Dirac's quantization condition.
Mar
4
answered The Aharonov-Bohm effect is purely classical, right?
Feb
26
awarded  Good Question
Feb
24
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Jan
20
awarded  Nice Answer
Jan
8
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Dec
7
awarded  Nice Answer
Nov
26
comment What are orbifolds and why are they useful and interesting for physics?
@Siva This observation is based on the solution of Schrödinger equation on a two dimensional cone where the energy eigenfunctions become more concentrated around the tip as the cone's half angle becomes smaller.
Nov
22
awarded  Good Answer
Oct
30
comment Aharonov-Bohm Effect and Flux Quantization in superconductors
They showed that the Shrödinger wave function of a single particle acquires a phase under a translation and a boost and this is alright, but, under a sequence of transformations: translation, boost, reverse translation, reverse boost, the overall phase does not vanish even though we returned to the initial frame of reference. This is a multivalued function related to the nontrivial central extension of the Galilean group.
Oct
30
comment Aharonov-Bohm Effect and Flux Quantization in superconductors
@jinawee Wigner worked on the representations of the Galilean group together with Inönü in their article "Representations of the Galilei Group". Please see the article on page 359 of Wigner's collected work: books.google.co.il/….
Oct
8
comment Spacetime Torsion, the Spin tensor, and intrinsic spin in Einstein-Cartan theory
Sorry, the first sentence in my comments should be: The scalar and Dirac field examples were not given for the purpose of showing how to couple torsion to classical fields, they were given as examples of matter.
Oct
8
comment Spacetime Torsion, the Spin tensor, and intrinsic spin in Einstein-Cartan theory
The answer to your second comment is that nothing was added by hand, the coupling term is obtained according to the rules of the minimal coupling. The only manipulation done is to separate the symmetric part of the affine connection and include it in the spin connection, and writing the antisymmetrical components separately giving the interaction term. In summary, the coupling of the matter fields to Einstein-Cartan theory can be viewed as a stage in the determination of its spin tensor.