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location Singapore
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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.

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Dec
25
awarded  Yearling
Nov
30
comment History of QFT after 1973
Come on, this can't be too broad, books that systematically account for the QFT history after 1970s must be very rare.
Nov
28
revised About interchange phase of identical particles in Weinberg's QFT book
deleted 115 characters in body
Nov
27
comment Does the lagrangian contain all the information about the representations of the fields in QFT?
@glance, "why can't I say (or can I?) that Aμ is a spin-1 field for that choice of the Lagrangian?" Yes you definitely can, then the reason to reject (2) becomes the energy bounded below condition, instead of the one Schwartz gave. Qmechanic's comment is right on.
Nov
21
comment Why isn't the path integral defined for non homotopic paths?
+1, informative answer. To nitpick on the terminology, by covering space you actually mean universal covering space.
Nov
17
comment Minimization of a quaradic-like expression when calculating the generating functional for free Dirac field
$\psi,\bar{\psi}$ are treated as independent variables, so the correct analogy here is $y^TSx$, which is still a quadratic form.
Nov
17
comment Minimization of a quaradic-like expression when calculating the generating functional for free Dirac field
1.If minimizing grassman valued function has a meaning at all, then just do partial differentiations and set them to be 0; 2. it certainly is formally a quadratic form, what's your definition of "really a quadratic form"?
Nov
13
comment Are relative phases observable for identical particles but not for non-identical ones?
I suppose it ultimately boils down to superselection?
Nov
13
comment Are terms with spinors analogous to $ ( \partial_\mu \Phi )(\partial^\mu \Phi)$ forbidden in the Lagrangian?
Regarding renormalizability @AndrewMcAddams raised a nontrivial question, but at least let's say such term can't coexist with a conventional Dirac fermion.
Nov
13
comment Are terms with spinors analogous to $ ( \partial_\mu \Phi )(\partial^\mu \Phi)$ forbidden in the Lagrangian?
Sorry I made a mistake, exactly because of the reasoning I mentioned above, it is not about how many spinors you have in the term, it is about how many $\gamma_\mu$ you can sandwich, e.g. $\bar{\psi}\gamma^{\mu}\gamma^{\nu}\psi$ will transform like a rank-2 tensor. I had the instinctual impression that your term isn't invariant because one of your matrix is put in front, not sandwiched. But again it could be my misunderstanding of your notation, in that case I should retreat to my earlier statement about renormalizability.
Nov
12
comment Are terms with spinors analogous to $ ( \partial_\mu \Phi )(\partial^\mu \Phi)$ forbidden in the Lagrangian?
BTW, this is also the reason why people sometimes say "a spinor is half of a vector."
Nov
12
comment Are terms with spinors analogous to $ ( \partial_\mu \Phi )(\partial^\mu \Phi)$ forbidden in the Lagrangian?
vector transformation induced by $\partial_\mu$. As you see, we must be able to sandwich the gamma matrix to induce a vector-like transformation, so for each $\partial_\mu$, we need two spinor fields.
Nov
12
comment Are terms with spinors analogous to $ ( \partial_\mu \Phi )(\partial^\mu \Phi)$ forbidden in the Lagrangian?
@JakobH, I'm not entirely sure about your notations, but if you $\sigma_\mu$ has a similar role as Dirac's $\gamma_\mu$, then you can think about why $\bar{\psi}\gamma^{\mu}\partial_{\mu}\psi$ is invariant. Note $\gamma_\mu$ are just coefficients, they don't really transform upon a spacetime transformation, only $\psi$ transforms. What is going on is each $\psi$ , upon lorentz transformation, contribute a matrix transformation $S$ in spinor rep, and because of the algebraic fact $S^{-1}\gamma^\mu S=(\Lambda^{-1})^{\mu}_{\nu}\gamma^\nu$, it cancels the
Nov
12
comment Are terms with spinors analogous to $ ( \partial_\mu \Phi )(\partial^\mu \Phi)$ forbidden in the Lagrangian?
@JakobH, Maybe I don't fully understand your notation, but you proposed term doesn't even look lorentz invariant. For every 4-vector $\partial_\mu$ you would need two spinor fields $\Psi$ to make the invariance, while your term has two $\partial_\mu$'s but only two $\Psi$'s
Nov
12
comment Are terms with spinors analogous to $ ( \partial_\mu \Phi )(\partial^\mu \Phi)$ forbidden in the Lagrangian?
The term you proposed with spinors will have mass dimension 5, so is not renormalizable. In the light of modern understanding of renormalization, non-renormalizable terms are less of a taboo than they used to be, but if one is only concerned with low energy regime, they won't be very interesting.
Nov
5
accepted Renormalization condition: why must be the residue of the propagator be 1
Nov
5
comment Help to understand vertex function
In fact it corresponds to a dressed photon line with a bare photon line stripped away at the external end, see the diagrams I drew in physics.stackexchange.com/questions/29890/… and in physics.stackexchange.com/questions/70882/…
Nov
3
answered Off-shell external line
Oct
27
awarded  Necromancer
Oct
22
comment Position operator in QFT
+1. Related:physics.stackexchange.com/questions/83251/…