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The Theoretical Physics site didn't have enough activity during the beta. It has been closed, and its content has been merged into Physics. You can download the data dump of all questions here, or visit the Theoretical Physics chat.

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Theoretical Physics

Q&A site for research level questions in any area of mathematical or theoretical physics.

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Help pick the subdomain for the site: discuss.area51.stackexchange.com/questions/2814/… – Joe Fitzsimons Sep 7 '11 at 6:01

25
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4
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Should some discuss.a51.se questions be migrated to per-site metas when betas begin?

aug 10 '15 at 1:27 Community♦ 1
18
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20
answers

What should the Theoretical Physics sub-domain be?

aug 4 '13 at 9:39 dimension10 474
28
votes
6
answers

Two level model (MO/Math.SE) vs one level model (SO)

dec 8 '11 at 15:53 Community♦ 1
6
votes
3
answers

Disposition of “Theoretical Physics”

sep 25 '11 at 19:19 Community♦ 1
-3
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0
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Proposal: A new, three-tier model for physics Q&A sites on StackExchange? [closed]

sep 11 '11 at 21:51 UGPhysics 151

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61 Example Questions (7 closed)

active newest votes
up vote 20 down vote
Are there entangled states that do not violate any Bell inequality?
added by Anthony Leverrier Nov 13 '10 at 19:50
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up vote 20 down vote
What are the justifying foundations of statistical mechanics without appealing to the ergodic hypothesis?
added by Marcin Kotowski, edited by WikiSpeedia hang-around Nov 16 '10 at 10:56
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2  
Great example. There is a lot of confusion about the subject. Especially since ergodicity is absolutely unnecessary to the foundations of stat mech. – Raskolnikov Nov 16 '10 at 11:06
@Raskolnikov: I quite agree with you except that I wouldn't go as far as to say absolutely. There are lots of interesting connections between ergodic theory and statistical mechanics. But I guess absolutely unnecessary is a great deal better than absolutely necessary which is what is still being taught in lots of physics classes. – Marek Nov 16 '10 at 11:50
up vote 19 down vote
Has [specific toy model] been studied in the literature?
added by Joe Fitzsimons Nov 13 '10 at 18:35
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up vote 19 down vote
Are XXZ spinchains with uniform couplings exactly solvable?
added by Joe Fitzsimons Nov 13 '10 at 18:38
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up vote 19 down vote
Within Twistor String Theory (ala Witten), what is currently seen as the significance of the superconformal algebra realized on supertwistor space.
added by Sarah Kavassalis Nov 14 '10 at 19:07
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Great to see you here Sarah, and great question. – Joe Fitzsimons Nov 14 '10 at 19:09
up vote 13 down vote
Is there a Majorana-like representation for singlet states?
added by Piotr Migdal, edited by WikiSpeedia hang-around Nov 16 '10 at 10:58
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I am not sure I understand the question properly, so just to clarify: by singlet states do you mean states with spin zero and by Majorana-like do you mean that particle is its own antiparticle? Then sure, this corresponds to real scalar field whereas complex scalar field gives you "Dirac singlet states" (which can, in principle, carry a charge). But if you meant it in this way then I think it's way too basic. However, opinions can surely vary on what is considered basic. – Marek Nov 18 '10 at 11:29
I think the question refers to the Majorana representation of symmetric states, ie states of n qudits invariant under a permutation of the qudits. See for instance arxiv.org/abs/1001.0343 – Anthony Leverrier Nov 23 '10 at 23:17
up vote 12 down vote
Does the quantum field theory of the standard model have a Landau pole?
added by Dave Bacon Nov 14 '10 at 19:59
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up vote 6 down vote
Are there any experimental results for [theoretical work]?
added by Piotr Migdal Nov 14 '10 at 17:04
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up vote 6 down vote
What is the current state of research on [a theoretical physics research program]?
added by Frédéric Grosshans, edited by WikiSpeedia hang-around Nov 16 '10 at 10:53
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The example I had in mind writing this question: trying to deduce quantum mechanics from a set of information theory related axioms. – Frédéric Grosshans Nov 15 '10 at 10:05
Is the purpose of this site for people to write mini-reviews about their field? I would prefer to see focused questions. – j.c. Nov 18 '10 at 19:42
up vote 6 down vote
Since we now believe that neutrinos have mass, does this mean there is a reference frame where the helicity of the neutrino is right handed?
added by Dave Bacon Nov 14 '10 at 20:21
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I would actually put this on the current physics site, since I'm pretty sure the answer is "yes," and it's not hard to explain why. It strikes me as the kind of thing researchers would consider fairly obvious. – David Z Nov 16 '10 at 4:49
up vote 6 down vote
Does Loop Quantum Gravity imply (measurable) dependence of the speed of light on energy?
added by Marek Nov 14 '10 at 21:38
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up vote 5 down vote
Which physical materials have a phase transition in the 3D Ising universality class?
added by Blake Stacey Nov 14 '10 at 20:11
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If the question stood "Which models..." I'd have liked it. This way it looks a bit too experimental. But I am not sure. – Marek Nov 14 '10 at 21:34
I see your point; on the other hand, a theorist might be approaching the subject from, e.g., highly mathematical papers on conformal field theory and be looking for something a little more physically grounded. – Blake Stacey Nov 15 '10 at 18:58
@Blake: I guess you are right. As pointed out elsewhere on this site: asking for physical evidence for a given model is definitely on-topic. Only asking for a concrete realization of some experiment (or problems thereof) is probably off-topic. – Marek Nov 16 '10 at 11:55
I don't see how probing how relevant theories are to real materials is off topic..? Or perhaps my idea of physical theory doesn't quite coincide with everyone's. – j.c. Nov 18 '10 at 19:41
up vote 5 down vote
Why does general relativity in 2+1 dimensions only have topological degrees of freedom?
added by Blake Stacey Nov 15 '10 at 18:59
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Maybe not a research-level question, but it seems plausible that a non-GR-specialist would ask something like it. – Blake Stacey Nov 15 '10 at 19:03
up vote 5 down vote
What are promising methods for creating artificial non-abelian gauge fields in trapped neutral atoms?
added by Frédéric Grosshans Nov 18 '10 at 17:29
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2  
Lifted from ABO to see if experimental question would be welcome on this site. As said by @Joe Fitzsimons, it's up to the community to decide, and if "if experimental questions become accepted as good on-topic examples we could change the title to reflect the broadened scope. " – Frédéric Grosshans Nov 18 '10 at 17:32
2  
@Frédéric: I am a pure theoretician but you got me hooked with the question. Let's see what others think. – Marek Nov 18 '10 at 19:35
1  
@Marek : The credit should go to @Matthias Rosenkranz : He proposed this question on AMO – Frédéric Grosshans Nov 19 '10 at 15:05
up vote 4 down vote
Why does Witt algebra have to be extended to Virasoro algebra with nontrivial central charge upon quantization?
added by Marek Nov 14 '10 at 21:13
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up vote 3 down vote
What is the diamond norm useful for (alt: why yet another norm in quantum communication)?
added by Chris Granade Nov 14 '10 at 19:13
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up vote 3 down vote
What is known about the universality classes of [your favorite lattice model]?
added by Marek Nov 14 '10 at 21:21
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up vote 3 down vote
What is the largest experimental system that has been analysed using a realistic first-principles open quantum system model?
added by user23893 Nov 14 '10 at 22:48
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up vote 3 down vote
What is the threshold for robust 2-D classical memory under a noisy application of Toom's rule?
added by Jim Harrington Nov 15 '10 at 6:59
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up vote 2 down vote
What are some most realistic stringy vacua found to date?
added by Marek Nov 14 '10 at 21:17
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up vote 2 down vote
What's the connection (if any) between topologically ordered many-body systems, and topological insulators?
added by seandbarrett Nov 15 '10 at 13:14
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up vote 2 down vote
Does Brazil nut effect depend on coefficients of friction and resitution? (theoretical, numerical and experimental answers appreciated)
added by Piotr Migdal Nov 15 '10 at 16:24
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Question posted deliberately to see if research-level questions not restricted to theory are welcome. Personally, I care much to have it as an example on-topic question in SE I would like to contribute. – Piotr Migdal Nov 15 '10 at 16:40
I see no reason for granular media physics to be excluded from theoretical physics. – Frédéric Grosshans Nov 15 '10 at 23:05
I think no-one is going to question granular media. On contrary, some may not want to have here experiment. – Piotr Migdal Nov 18 '10 at 17:32
up vote 2 down vote
Are knot invariants relevant to four-dimensional gauge theories?
added by John Joseph M. Carrasco Nov 16 '10 at 7:28
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up vote 1 down vote
Citations for using topological degrees of freedom to store quantum information?
added by Chris Granade Nov 14 '10 at 19:15
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up vote 1 down vote
What is the current thinking about Lisi's "Exceptionally Simple Theory of Everything"? [closed]
added by Dave Bacon Nov 14 '10 at 20:25
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closed as off topic by Marcin Kotowski, Anthony Leverrier, Marek, rz_, Daniel Nov 14 '10 at 22:48

This question does not relate to the topic of the proposal.
It was closed as part of an automated migration of off-topic to close votes on September 29, 2011.

As far as I understood (i.e. not much), Lisi's "Exceptionallay simple" theory has been first found interesting by some theoreticians. Then it has been found "too simple". Why flag it off-topic ? – Frédéric Grosshans Nov 17 '10 at 9:32
3  
@Fréderic: I think it is by now a common knowledge in the theoretical community that this is just a crackpot theory. Physics.SE should be fine to answer this sort of questions (e.g. recently they answered something similar about the Heim theory). – Marek Nov 17 '10 at 16:28
@Marek : thanks for the clarification – Frédéric Grosshans Nov 18 '10 at 10:55
up vote 1 down vote
I heard gravitation can be reformulated as a gauge theory. How precisely does the correspondence work and what are some papers on the subject?
added by Marek Nov 15 '10 at 13:27
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I think this is too basic; a very quick Google or arXiv search would yield the answer. – Sarah Kavassalis Nov 16 '10 at 3:28
2  
@sk Oh I don't know about "the answer" ;-) -- although I agree that the question's possibly a little broad to headline as a "great" example . I could see the discussion spanning: gravity as double-copy of gauge theories via color-kinematic duality, or gravity from KLT relations, or AdS/CFT, or FRW/CFT, or even Andy's recent Kerr black hole stuff. I'd see the precise workings of any of those being worthy of current and active research-level discourse. Even the most-well studied correspondence AdS5/CFT is certainly not a closed subject. – John Joseph M. Carrasco Nov 16 '10 at 7:03
1  
@Sarah: the same thing can be said about lot of other questions here. I am not sure whether you want to prohibit asking about anything that can be find on arXiv (which is basically everything there is). @sk: Yes, I realized the question might be too broad. Still, it's something that (say) a GR student with a little knowledge of gauge theories might be interested in (and your "answer" is fine). Maybe not a great example but to me it seems certainly nice and relevant question. – Marek Nov 16 '10 at 7:52
@John: I realized that your comment wasn't targeted at me. FYI though, I think you need at least three (consecutive?) letters for @ to work. – Marek Nov 16 '10 at 8:01
@John I completely agree with you. I probably should have said that I thought it was too basic/general of a question, as phrased (also, I'm not a fan of the "what are some papers on this" type questions, unless it's on a very precise topic, when those are pretty easy to find without stackexchange). The precise workings of any area of gauge-gravity duality are certainly worthy of discussion. – Sarah Kavassalis Nov 16 '10 at 15:04
up vote 1 down vote
What is a good introduction to Topological Quantum Field Theory? Specifically it being used in Quantum Computation.
added by Peadar Coyle Nov 18 '10 at 9:12
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up vote 1 down vote
Can anyone explain the details about the Clay Prize Problem on Yang-Mills and the Mass Gap problem?
added by Daniel Nov 23 '10 at 22:38
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up vote 0 down vote
Why is the sky blue during the day, red during sunrise and sunset and black during the night? [closed]
added by Tsuyoshi Ito Nov 13 '10 at 21:46
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closed as off topic by Matt Reece, Joe Fitzsimons, Marcin Kotowski, Wikis, Cedric H. Nov 14 '10 at 18:20

This question does not relate to the topic of the proposal.
It was closed as part of an automated migration of off-topic to close votes on September 29, 2011.

3  
Copied from physics.stackexchange.com/questions/17/… to clarify the difference between the two proposals. (That is, this question is intended to be an off-topic example.) – Tsuyoshi Ito Nov 13 '10 at 21:47
1  
Excellent. Thanks Tsuyoshi! – Joe Fitzsimons Nov 13 '10 at 22:22
IMHO it should stay in physics SE (while interesting, it is not research-level, as the answer is widely known). – Piotr Migdal Nov 14 '10 at 18:50
@Piotr: I think most people agree with you, which is why there are 9 votes for it as being a good example of what is off topic. – Joe Fitzsimons Nov 14 '10 at 19:07
up vote 0 down vote
What is the current knowledge about counting mutually unbiased bases?
added by Marcin Kotowski, edited by WikiSpeedia hang-around Nov 16 '10 at 10:54
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1  
With one remark: I would prefer to have questions about a certain thing, not asking for a review of a subject. – Piotr Migdal Nov 14 '10 at 19:27
2  
You can easily rephrase the question as "How many MUBs can there exist in a given Hilbert space ?", then it's a question about a certain thing :) – Marcin Kotowski Nov 14 '10 at 19:30
What is the problem with a review ? – Frédéric Grosshans Nov 17 '10 at 14:21
up vote 0 down vote
Could teleportation ever really happen? [closed]
added by Wikis Nov 14 '10 at 21:27
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closed as off topic by Piotr Migdal, Jim Harrington, Georg Lind, Steve Flammia, Igor Ivanov Nov 15 '10 at 22:08

This question does not relate to the topic of the proposal.
It was closed as part of an automated migration of off-topic to close votes on September 29, 2011.

Probably off-topic. – Wikis Nov 14 '10 at 21:29
Added here: physics.stackexchange.com/questions/1203/… – Wikis Nov 22 '10 at 13:57
up vote 0 down vote
Is there a fundamental reason why the number of quark generations and lepton generations must be equal?
added by Tracy Hall Nov 15 '10 at 7:59
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I would argue that this could actually go on the current Physics beta site, since the answer involves intro-level quantum field theory. – David Z Nov 16 '10 at 2:25
@David: I am not really sure I would call the answer intro-level (e.g. the level of my intro QFT course was certainly much much lower). Also, I don't think the majority of the community at the physics.SE would appreciate the details of the anomaly cancellation. The community of this site, on the other hand, might (at least the ones who don't yet know the answer). So I think it's a fine question for (say) grad student to ask, even though it's not strictly research level (although it might be reformulated to include SUSY and other stuff). – Marek Nov 17 '10 at 15:17
1  
@Marek: okay, maybe not exactly intro-level. Intermediate, perhaps. Still, I think that any research-level physicist on this site would either already know about the anomaly cancellation, or wouldn't particularly care because it's irrelevant to their research area. Plus, questions like this, concerning the established foundations of physics at an advanced undergrad/early graduate level, are exactly what we're trying to encourage on the current physics SE site. – David Z Nov 17 '10 at 19:05
@David: I see, I wasn't aware of this. In that case I am afraid that some of my own proposed questions here would be better suited to physics.SE. Although it has to be said that they got quite a few votes already (possibly because people made the same assumption as I did that graduate-level questions are still fine for TP.SE). – Marek Nov 18 '10 at 0:28
@Marek: Your other proposed questions actually do seem more geared toward current research than this one (although there would be no harm in asking them on physics.SE if you want). The standard model is fairly well-established physics. Anyway, I think this question is right about where I'd like to see the boundary set between the two sites, so it could fit in on either one. But physics.SE needs high-level questions to help keep the pop-sci stuff from taking over, whereas that's not at all a concern for TP.SE. So if I had to pick only one place for this question, it'd be physics.SE. – David Z Nov 19 '10 at 22:40
show 1 more improvement suggestion
up vote 0 down vote
Two CdL bubbles embedded in higher dim collide. Prior to collision only subset of dimensions were shared. Possible grav waves in subsequent evolution?
added by John Joseph M. Carrasco Nov 16 '10 at 7:23
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up vote 0 down vote
Has it been experimentally verified that the best ratio of trap depth to temperature for evaporative cooling to Bose-Einstein condensation is 10?
added by Abe Nov 16 '10 at 14:20
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up vote 0 down vote
In arxiv:XXXX.XXXX on the topic of Y what do the authors mean by saying that [complicated expression]?
added by ihuston Nov 17 '10 at 11:29
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up vote 0 down vote
What's a good review article covering the likely obstacles between current fusion experiments (e.g., ITER and NIF) and commercial fusion power?
added by Bill Kaminsky Nov 19 '10 at 20:41
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up vote 0 down vote
Can closed timelike/null curves exist in classical/quantum gravity? Does it require exotic matter, or violations of averaged null energy conditions?
added by Jason Nov 20 '10 at 17:25
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up vote 0 down vote
Why is it said that the muon - hydrogen observations contradict with the Standard Model or just QED? What about QCD non-perturbative corrections?
added by Mateusz Iskrzynski Nov 20 '10 at 22:07
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quite a hot and discussed topic, at an academic level – Mateusz Iskrzynski Nov 20 '10 at 22:08
up vote 0 down vote
Are quantum gates [BLAH] and [BLAH] universal for quantum computing?
added by Tez Nov 21 '10 at 19:06
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up vote 0 down vote
Applying a continuum theory (e.g QFT) to a naturally discrete setting results in corrections/refinement. give one example of this per answer!
added by Kaveh_kh Nov 22 '10 at 16:20
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