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Sep
27
answered What is the difference between D branes, M branes, and NS branes?
Sep
25
answered Do gravitational fields exist in vacuum region?
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
answered Mathematical approximation to physics
Sep
20
answered Massless integrals in dim-reg
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
revised Unitarity and renormalizability
added 65 characters in body
Sep
20
answered Is the ground state of a QFT always a pure state? And excited states are mixed?
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
answered Unitarity and renormalizability
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.
Sep
18
comment Is there a reason why the spin of particles is integer or half integer instead of even and odd?
Ah, I see. I'm sorry about that. If you do a typical undergraduate course on classical mechanics (meant for physicists), you might learn enough about Lagrangians, Hamiltonians, symmetries and "generators" to get the flavour of my answer. If you follow that up with an undergraduate course on quantum mechanics, then hopefully my answer will make sense.
Sep
17
comment Why are non-Abelian gauge theories Lorentz invariant quantum mechanically?
Gauge theories have Ward identities. So yes, your amplitude might naively have spacetime indices, but when you contract it with the polarization vectors of the gluons, the spurious dependence is supposed to vanish (transverse modes, little group, etc).
Sep
17
comment Can quantum vacuum carry entropy?
@MrFermiMr: What do you mean by entropy? How do you define it?