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Hi, I am a string theorist and a publicist.


Dec
15
answered Which collision energy at LHC is better for hunting 125 GeV Higgs, 7 TeV, 8 TeV or 14 TeV?
Dec
15
comment Value of the Hubble parameter over time
In GR, one has to be careful what we mean by "non-accelerated expansion". In the "explosion in flat space" model, we would mean that $v=Hd$ is constant. In this model, we may just calculate the time, $d/v$ (because $s=vt$), when the distances were zero, and we get $1/H$. That's a possible interpretation in GR, too. However, that's different from a "constant $H$". In our Universe, $H$ is ultimately going to be nearly constant. But this corresponds to exponential, not linear, growth of distances, $d\sim \exp(Ht)$ because $\dot d = v = Hd$ where $H$ is fixed.
Dec
15
comment Value of the Hubble parameter over time
Well, @Udo, indeed, the fact that the expansion is accelerating means that the distance between two galaxies isn't growing linearly but faster than linearly - the slope increases. The slope is the velocity and the increase of the velocity with time is acceleration. I would have made a bet that your confusion had nothing to do with some subtleties of GR and it would be equally real if one just modeled the expansion as galaxies exploding and going away from each other in external flat spacetime.
Dec
15
comment Higgs boson and string theory
"I don't agree that these slightly split models with 10 TeV scalars are more "stringy" than "QFT-like," since all of the calculations are done in effective supergravity theories" - Well, unless extra dimensions are large or very warped, all physics below $10^{18}$ GeV or so will always be dominated by calculations based on QFT and SUGRA. This doesn't mean that all of these calculations are equally stringy or non-stringy, does it? String/M-theory simply has different "naturalness" standards than QFTs. One may even say that things like grand unification are "more stringy" than bare MSSM.
Dec
15
comment Hidden observers in Double Slit experiments - Do they matter?
"But quantum amplitudes are not probabilities, and they are shrunk in this way after a measurement." Dear @Ron, quantum amplitudes and probabilities are related in a straightforward way: probabilities are squared amplitudes (in absolute value), or sums of such squared terms. Because this is a purely mathematical operation, it's clear that one must assign the same qualitative interpretation to both. So quantum amplitudes are (quantum-completed) probabilities. They surely can't be "more tangible" than probabilities - you couldn't get an "untangible" thing by squaring a tangible one.
Dec
15
comment Higgs boson and string theory
Plus one, Matt. I think that the MSSM is still being given too much credibility relatively to other SUSY theories/limits but your answer was ordered, anyway.
Dec
15
comment The implication of anti-commutation relations in quantum mechanics
For fermionic operators to anticommute is equally natural and "classical" as for bosonic ones to commute. If you construct an actual number as a product of an even number of fermionic operators, this number will indeed commute with other numbers if the factors commute or anticommute. In fact, with some contrived (and not canonical) redefinitions of signs, anticommuting operators may be converted to commuting ones. It's just much more natural to use anticommuting numbers for fermions.
Dec
15
comment Has CERN recently found evidence for a Z-prime boson?
Haha, you're trying to read a lot, indeed. Let me just guess that "Fabio knows" almost certainly doesn't mean "Fabiola knows". The former is male, the latter is female. It could be Fabio Maltoni see e.g. arxiv.org/abs/hep-ph/0505014 or someone else.
Dec
14
comment Why search for theoretical particle?
One could argue that this question deserves to be closed according to 4 out of 5 criteria in the list. But before we may meaningfully answer, I would like to know what kind of an answer we should be trying to offer. So let me ask Daniel Leung: Just out of curiosity, what is the purpose of your life, something that consumes place on Earth and resources that could be much more meaningfully used for scientific research, for people who actually create some values? Does your life allow me to learn the shape of the hidden Calabi-Yau dimensions? Build a stronger accelerator? Or something else?
Dec
14
answered Higgs boson and string theory
Dec
13
revised What's the Standard Model width of a 125 GeV Higgs?
added 210 characters in body
Dec
13
revised What's the Standard Model width of a 125 GeV Higgs?
added 210 characters in body
Dec
13
answered Are there any models for two light Higgs?
Dec
13
answered What's the Standard Model width of a 125 GeV Higgs?
Dec
13
comment Convergence of quantum effective action to finite loop order
Dear @Squark, I don't think it's possible to treat these two limits differently in any real situation. The real expansion parameter measuring "how much quantum" the theory is - how important the loops are - is always the same. For the electromagnetic interaction, it's the fine-structure constant $e^2/(4\pi \epsilon_0)\hbar c$. This is small, $1/137$, and that's why the loops - or additional external legs - bring suppression. Your unusual asymmetric limit seems to depend on an arbitrary renormalization of the fields by a power of $\hbar$ which is unphysical.
Dec
12
comment Status of the little hierarchy problem
The newest paper with "little hierarchy problem" in the title is one from May 2011 by Feldman, Kane, Kuflik, Lu: arxiv.org/abs/arXiv:1105.3765 - those gravitinos and moduli around 30 TeV do solve it, aside from other problems. Another 2011 paper: arxiv.org/abs/arXiv:1104.3171
Dec
12
comment Theoretical proof forbidding Loschmidt reversal?
Quantum mechanics really forbids the kind of detailed microscopic control that would be needed for the Loschmidt reversal. While in classical physics one could say that for most initial states, the entropy will increase, while for a carefully selected special initial state, it may decrease, quantum mechanics says something else. It always predicts the probabilities only and the probabilities of a big decrease in entropy is small for every initial state, much like if one averages over initial states in classical physics.
Dec
12
comment Hidden observers in Double Slit experiments - Do they matter?
Dear @Peter, you seem to refer to Bohr's quantitative "complementarity" which allows a "partly wave-like" and "partly particle-like" behavior of a quantum of the field. That's OK and you're right but that's not really what the original question was about. The original question talked about the situation when some apparata are completely able to measure the which-slit information (so the action change is very large, in your language), but this measurement isn't accessible to "us". So your answer is arguably off-topic.
Dec
12
comment Are there irreducible tensors of half integral degree in quantum mechanics?
Dear @Friedrich, $J_\pm$ is the same thing as $J_x\pm i J_y$, up to the sign of $i$ and the overall normalization, so the difference between $\{J_x,J_y,J_z\}$ and $\{J_+,J_-, J_z\}$ is just a convention about the basis - which linear combinations of the three quantities are being written as the standardized ones. The 3D space of linear combinations of these 3 tensor operators is exactly the same in both cases. That's why we say that the $j=1$ irreducible representation of the group is unique. The same hold for any allowed $j$, too.
Dec
12
answered Interplay between the cosmological constant and “microscopic” properties of string vacua