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To pursue a PhD in theoretical high-energy physics, one needs to be half retarded and half advanced -- half-advanced for wanting to capture the excitement of the past, and half retarded for seeing a future in it.


May
21
comment What is meant by the phrase “this operator does not renormalize this other operator”, and how can understand it using diagrammatic arguments?
BTW, this recent paper might be of interest: arxiv.org/abs/1505.01844
May
16
comment Can bosons have anti-particles?
Taylor's point seems to be centered on the following idea "Bosons operate under different laws and can be created singly. This is a crucial distinction and is in nature of being either matter particles or force carriers." (which I simply don't understand)
May
16
comment Can bosons have anti-particles?
By definition charge conjugation $C$ is that operator which swaps particles and anti-particles. And I have to agree with @innisfree.
May
16
comment Can bosons have anti-particles?
Would you call the Higgs (doublet; not just the radial mode) an elementary scalar that is electrically carged?
May
15
awarded  Nice Answer
Mar
11
comment Why are $SU(N)$ gauge theories easier to handle for $N\rightarrow \infty$?
It's an expansion parameter, like any other. In the large-N limit, many diagrams become sub-dominant. So it's enough to deal with a dominant diagrams, which are easier to deal with.
Mar
11
revised Why are $SU(N)$ gauge theories easier to handle for $N\rightarrow \infty$?
"Simple" in the context of a lie group means something very specific -- and SU(N) is not "simple" in that sense.
Mar
3
revised What does it mean to have a degenerate $S$-matrix?
deleted 156 characters in body
Mar
3
answered What does it mean to have a degenerate $S$-matrix?
Mar
3
comment Notion of distance in a Conformal Field Theory
To add to my comment above, if distances really did not matter, then you are wrecking serious havoc with the notion of locality/causality! (You most definitely don't do that in a conformal quantum field theory)
Mar
1
comment Notion of distance in a Conformal Field Theory
"In a conformal field theory, due to the scale invariance only angles - and not distances - matter." That's not quite true! All that scale invariance guarantees you is that things transform nicely as you zoom in and zoom out. You don't see something weird happening as you zoom past a special scale. So one can pick a scale unit for calculation, and then ensure that all physical answers are non-dimensionalized by the same unit, so that they respect scale invariance.
Feb
27
awarded  Autobiographer
Feb
18
comment How does the notion of topological order relate to the Landau-Ginzburg theory of phase transitions?
Are both 1 & 2 necessaary, or are they only heuristic indicators? Does entanglement structure undergo any change across a spontaneous symmetry breaking transition, which could have been described in the LG paradigm? Or would the possible existence of local order parameters preclude you from calling these quantum phase transitions?
Feb
15
comment How to compute this loop integral?
Ah, those slides start with the Feynman rules for scalar+gauge theory but then switch to QED. The way to write the numerators is to start at a particular vertex or propagator, and then go around the loop. Since this diagram has only bosons, the order in which you multiply contributions from the vertices and propagators will not matter. If you had QED, for example, the $\gamma$-matrices on the fermion-fermion-photon vertices would not commute and you would have to keep careful track of the ordering.
Feb
15
answered How to compute this loop integral?
Jan
24
comment Is there a simple layman way to explain the incompatibilities between quantum mechanics and (general) relativity to high school students?
Read the first paragraph here: en.wikipedia.org/wiki/D-brane#Theoretical_background
Jan
24
asked How does the notion of topological order relate to the Landau-Ginzburg theory of phase transitions?
Jan
8
revised Stack presentations and massive non-conformal theories
deleted 2 characters in body; edited title
Dec
31
comment Branch cuts in two-point function
Read on below eqn (7.20) in P&S. The threshold is given by the sum of masses of the two particles of the two-particle state, and those (pole) masses are well-defined and scheme independent.
Dec
24
comment Are all fermions massless at high temperatures?
For comments on finite temperature field theory in general, there are tons of reviews or lecture notes or even a few textbooks. I think some of them should mention this point paranthetically.