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19h
comment Effective Field Theories of QCD
@soliton: If you've made any progress in the course, you might be able to answer your own question. I think it will help many others :-)
1d
comment Is there some special case where a fermion can mediate a force?
@arivero, I understand and for the same reason, my answer is measured.
Oct
18
comment Is there a connection between the fluctuation-dissipation theorem and the Green–Kubo relations?
her book :-)
Oct
13
comment $D$-brane and 5th dimensions
The "p" in p-brane stands in for the number of spatial dimensions that a brane covers. The "D" in D-brane stands for something quite different: It states that this brane provides "Dirichlet" boundary conditions for the strings roaming around in space.
Oct
12
comment Gravity as a gauge theory
Though this might not be what the OP had in mind, a recent concept that is becoming interesting is that a gravity theory could be thought of as a product of two copies of gauge theories. For eg, look at: arxiv.org/abs/1004.0476
Oct
8
comment Scalar field divergent mass correction interpretation question (hierarchy problem)
"it's telling me that I have a correction as big as the largest scale in my problem (cut-off scale)" -- that's not quite true. Any corrections to the mass are suppressed by positive powers of the loop factor $\frac{g^2}{16 \pi^2}$.
Oct
3
comment Dilaton field and Scale symmetry breaking
Interesting question. From what I understand, you are asking how SSB of scale symmetry in QFT (by dimensional transmutation) can be seen from the perspective of the dilaton. I wonder if one can do a spurion analysis.
Oct
3
comment Calculate the equivalent resistance between A and B
For more information on how to approach "unbalanced" bridges, check here: ibiblio.org/kuphaldt/electricCircuits/DC/DC_10.html
Oct
3
comment Calculate the equivalent resistance between A and B
This setup is called the Wheatstone bridge. Since the bridge is "balanced" (read he Wikipedia article) there will be no current in the $5 \Omega$ resistor and you can essentially "disconnect" it.
Sep
27
comment What does it mean to “convert energy into time”?
Quite possibly slips between what the scientist intended to say, what was actually said, what was heard by the journalist, what the journalist thought was said, what the journalist expressed that as, in the article and what the editor thought it should be written as.
Sep
25
comment Do gravitational fields exist in vacuum region?
Defining the notion of "energy" in general relativity is a tricky thing -- en.wikipedia.org/wiki/Mass_in_general_relativity
Sep
21
comment Is the ground state of a QFT always a pure state? And excited states are mixed?
Practical comment: Based on my experience, I would suggest you to be cautious about taking statements at face value, in that line of the literature (EE+holography, etc). I got the feeling that people sometimes overstated the generality of their result which might be based on a very specific computation.
Sep
21
comment Massless integrals in dim-reg
Observation: When the higgs mass is set to zero, the SM is classically scale invariant. So, the question is, can that symmetry be broken quantum mechanically, and if so, will it be suppressed in any manner.
Sep
20
comment Massless integrals in dim-reg
Ah, I see. I don't have a general picture of the kind of applications you're talking about. Some links might help.
Sep
20
comment Massless integrals in dim-reg
Btw, scitation.aip.org/content/aip/journal/jmp/15/1/10.1063/… might be of use if you can access it.
Sep
20
comment Massless integrals in dim-reg
What if I use the "prescription" to regulate the UV first and then regulate the IR (...one problem at a time?)
Sep
20
comment Massless integrals in dim-reg
Could you add links to the 't Hooft-Veltman conjecture, and an example showing the way it's being used?
Sep
20
comment Chiral anomalies
In particular, chiral anomalies are possible when you have "chiral currents" in your theory, i.e. only the Left (or right) handed fermions are charged under some symmetry. Since in the SM, only left-handed fermions are charged under the weak sector, one has to ensure that the gauge symmetry is kosher at the quantum level, and not "anomalous". My comments are very general (hopefully useful to someone) and you might already know all that, and be looking for something specific.
Sep
20
comment Chiral anomalies
Some general context: In QFTs, anomalies are fairly straight-forward to compute, at the one-loop level. In the case of the standard model, anomaly cancellation works out quite miraculously with unlikely looking cancellations among numbers that depend on the gauge charges -- giving rise to an expectation that there's some simpler UV picture from which these charges come out, and anomaly cancellation in that bigger picture might be easy to understand.
Sep
18
comment Is there a reason why the spin of particles is integer or half integer instead of even and odd?
The punchline then: Just like vectors and tensors, you can have these spin half things called spinors. The condition that all physical rules have to transform nicely under spacetime (Lorentz) transformations forces us to have only objects which transform as mentioned above. Beyond that, the convention for spins is such that $2 \pi$ represents a "full rotation". Unless you want to mess around with that, you don't want to redefine scaled charges.