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age 24
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Bachelor degree in Physics. Interested in mathematical aspect of quantum field theory(though ironically not mathematically enlightened, but in continuous training). Getting to know some basics of topological insulators. I will probably start pursuing a Phd in theoretical physics in 2014 or 2015.

I'm spending more time on www.physicsoverflow.org


Aug
19
awarded  Popular Question
Aug
18
comment EM wave function & photon wavefunction
@ArnoldNeumaier, I would say it is quite tempting to quantize them as fields, since $F^{\pm}$ naturally form the $(1,0)$ and $(0,1)$ representation of Poincare group, exactly the right representation to get helicity-1 particles. I think on the free field level this quantization is equivalent to the more conventional ones. Of course, with hindsight we know we won't be able to build up useful interactions with such fields.
Aug
18
comment EM wave function & photon wavefunction
@ArnoldNeumaier, I was just applying the U(1) invariance trick in the most commonly used context, i.e. field theory, and there's no problem in interpreting Riemann-Silberstein vectors as fields. I guess one can work in wavefunction context and require the derivative to be covariant to avoid renormalizablity issues, but my line of thought was, since field theory is the best we have at hands, it is probably the best to work in such context. I guess my reasoning is fuzzy, because this U(1) trick seems to be somewhat superficial and does not directly bear a physical meaning.
Aug
17
comment EM wave function & photon wavefunction
@WetSavannaAnimalakaRodVance, I finally took a look at what one could get from imposing U(1) invariance on Maxwell equation(in the form of Riemann-Silberstein vectors $F^{\pm}$ to mimic Dirac equation). The problem is, if we write them in a Dirac lagrangian, we would have terms like $F^{-}\partial F^{+}$, but this is nonrenormalizable, and imposing gauge invariance also gives you nonrenormalizable interactions. So the physical relevance is pretty much killed, I don't know if it can be mathematically interesting.
Aug
3
comment I don't get band structure of solids
But it seems my vote is locked since I voted too long ago, sorry for that.
Aug
3
comment I don't get band structure of solids
Ok, I kinda what was going on. In fact OP's question can be interpreted in two ways, the first is "if energy levels of each individual atom are discrete, how come when atoms come together and form solid, they become continuous", to which your answer is the correct one. The second is "electron in the atom is bounded, hence the energy levels are discrete; now electron in solids is also bounded(by solid), then why aren't the energy levels discrete?", to which the answers saying "electron in solids is not really bounded, since we treat solid as infinite in extent" are correct.
Aug
1
comment I don't get band structure of solids
@GeorgeHerold I downvoted this answer a few days ago, for I held the same opinion as fqq expressed. I always thought bands by definition are functions of bloch momentum, so how can it be defined for nonperiodic system? I'd be happy to remove my downvote if it is clarified.
Jul
26
comment Is it really proper to say Ward identity is a consequence of gauge invariance?
@AndrewMcAddams: To me that really is just imprecise language he used. That's the only logical way I see to understand it and it fits well with rest part of the book.
Jul
26
comment Is it really proper to say Ward identity is a consequence of gauge invariance?
@AndrewMcAddams: he means with a full photon propagator attached but on top of that a bare photon propagator must be stripped away, just note he immediately added "...but with the complete Dirac external line propagators and the bare photon external line propagator stripped away."
Jul
26
comment Is it really proper to say Ward identity is a consequence of gauge invariance?
@AndrewMcAddams: (1) indeed does not contain an external photonic line. Where did Weinberg say so?
Jul
13
comment Free Particle Path Integral Matsubara Frequency
The other thing is, I think, interpreting $\prod_{n\in\mathbb{N}} \frac{T}{4\pi n^2}$ as $\lim_{N\to\infty}\prod_{n=1}^N \frac{T}{4\pi n^2}$ is already a regularization, i.e. lattice regularization, $\omega_n=\frac{2\pi n}{\beta}, n=0, \pm 1, \pm2,\ldots\pm \frac{N}{2}$, where $N=\frac{\beta}{\epsilon}$, and in such regularization $Z$ literally equals $\lim_{N\to\infty}\prod_{n=1}^N \frac{T}{4\pi n^2}=0$
Jul
13
comment Free Particle Path Integral Matsubara Frequency
emm, this won't address op's question in the comment: if $\prod_{n\in\mathbb{N}} \frac{T}{4\pi n^2}$ is already convergent(to 0), why do we still need to regularize?
Jul
2
awarded  Curious
Jun
27
awarded  Promoter
Jun
27
comment When can we take the Brillouin zone to be a sphere?
@Heidar: I plead you not to forsake this quetion :)
Jun
23
revised Topological insulators: why K-theory classification rather than homotopy classification?
added 412 characters in body
Jun
4
awarded  Popular Question
Jun
3
revised When can we take the Brillouin zone to be a sphere?
added 412 characters in body
May
28
revised When can we take the Brillouin zone to be a sphere?
added 617 characters in body
May
24
awarded  Popular Question