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4h
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.
22h
awarded  quantum-field-theory
23h
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
Jan
15
comment How to measure (missing) transverse energy
And the reason you use calorimeter deposits instead of just tracks is that you don't want to omit things like photons and $\pi^0$'s.
Jan
15
comment How to measure (missing) transverse energy
"How do you do that? Just by using 2-d vectors (only x and y coordinates)?" Yes.
Jan
15
comment How to find SUSY with near-degenerate masses?
These are events with a low cross-section and you can't rely on the high-momentum tail to boost the leptons above trigger thresholds. Although the actually difficult case, higgsinos, can give you >~10 GeV leptons some fraction of the time, but the rates are low and the backgrounds are large.
Jan
15
answered How to find SUSY with near-degenerate masses?
Dec
30
awarded  Custodian