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2d
awarded  quantum-field-theory
2d
answered Toy models of asymptotic safety?
Aug
26
comment Why should any physicist know, to some degree, experimental physics?
What do you mean by a "proper theoretical physicist"?
Jun
27
comment “Weakness” of gravitational force
General relativity works perfectly well as a quantum field theory of gravity as well. For instance, there are completely finite calculable quantum corrections to Newton's law that are insensitive to the UV completion.
Jun
26
comment “Weakness” of gravitational force
There is a field theory of gravity. It's general relativity.
May
3
comment Why is $S^1\times\mathbb{R}^{n-1}$ the topology of $AdS_n$?
The tensor product symbol $\otimes$ is sometimes used in physics when the product $\times$ should be. I don't know why. For instance, one sometimes encounters papers saying that the gauge group of the Standard Model is SU(3)$\otimes$SU(2)$\otimes$U(1). I don't know what that means. I think people use the notation because it makes them feel more "mathy" somehow.
Apr
20
comment Effective theories and dimension six operators
Operators with derivative couplings are considered frequently. And giving mass to neutrinos with dimension 4 operators requires the introduction of a field that isn't present in the Standard Model (a right-handed neutrino). In the Standard Model as an effective theory with fixed field content, the dimension-5 Majorana masses are the only possible neutrino mass. Which doesn't mean it's how neutrino mass works in the real world; we don't know yet.
Apr
20
answered Effective theories and dimension six operators
Apr
14
awarded  Nice Answer
Mar
27
comment Anomalously broken conformal symmetry
Conformal symmetry is not a symmetry at all in a theory with a conformal anomaly. I think I pretty much agree with all of your comments.
Mar
19
comment The BICEP2 data are evidence of gravitational waves and of inflation. Are they also the first observation that requires quantum gravity?
It's not the first evidence of gravitational waves or of inflation. It is the first evidence of gravitational waves from inflation, which implies a host of other things: a GUT-scale potential during inflation, a field range of more than M_Planck, extremely strong constraints on axions or other light scalar fields--I think it'll take quite a while to sort out all the implications.
Mar
10
comment Is it possible that the universe in its entirety is discrete rather than continuous?
No. You run into problems with violating Lorentz invariance, because special relativity is built around continuous spacetime. I mentioned some of the experimental limits at physics.stackexchange.com/q/26906.
Feb
18
answered Why can't dark matter be black holes?
Feb
17
comment Do photons and cosmic rays radiate energy through gravitational waves? If not, why not?
Maybe Cliff Burgess's review: relativity.livingreviews.org/Articles/lrr-2004-5
Feb
17
comment Do photons and cosmic rays radiate energy through gravitational waves? If not, why not?
No, it doesn't. General relativity coupled to the Standard Model is a perfectly good effective quantum field theory. The corrections we expect a complete theory of quantum gravity to compute would be tiny for questions like the radiation of gravitons from photons.
Feb
17
comment Do photons and cosmic rays radiate energy through gravitational waves? If not, why not?
It's not true that we lack of a theory of how photons radiate gravitons. It's described by general relativity.
Jan
24
answered AdS/CFT not dependent on validity of string theory
Jan
21
comment Does Super Mario physics work in reality?
The close votes are because it's a duplicate. But it's a much more amusing version of the old question. ("Lack of public investment in infrastructure" made me laugh.)
Jan
16
revised No non-trivial UV asymptotically free and IR free
added 716 characters in body
Jan
16
answered No non-trivial UV asymptotically free and IR free