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# Example questions

As this projects tries to some kind of restart the  (generalized) theoretical physics proposal outside the Stack Exchange network, conversely to Astronomy which has just made it to private beta again (congratulations!), we have no well-defined place to ask example questions.

May idea of a work around is to do it here in the comments below this short post. When asking one example question per comment, they can be voted on (up and down), and as comments to comments are possible, each question can be discussed a bit too if needed.

So let’s go 😉 !

1. Q: In the Green-Schwarz formalism, As there is a minus sign in the definition for the 3-form $\Omega_2=\text{d} {{\Omega }_{3}}=A\left( \text{d}{{{\bar{\Theta }}}^{1}}{{\gamma }_{\mu }}\text{d}{{\Theta }^{1}}-\text{d}{{{\bar{\Theta }}}^{2}}{{\gamma }_{\mu }}\text{d}{{\Theta }^{2}} \right){{\Pi }^{\mu }}$, does this mean that it applies to only the Type IIA String Theory, or something like that?

A: No, it doesn’t. It applies to the Type IIB String Theory too, the minus sign appears only because when it is multiplied with the definition of $\Pi^\mu$ (which takes a similiar form, with a + sign, the second-order terms that are not squares must disappear. You can see this by:
///…\\\

\
I’ll post some more tomorrow.

• Ok, done. Now you can remove the first question from the above comment^ (I can’t edit my own comments, only the post author (you) can).

• Mark Mitchison says:

Posted to see how experimental we are willing to go 🙂 As far as I know this is a research-level question, but obviously it’s about experimental physics…

2. Q: Why does the tachyon (in the RNS formalism) need to be GSO Projected out?

A: If one has a tachyon, then that means a system may lower it’s energy, even from the ground state, by releasing tachyons. This would mean that the ground state is unstable.

3. Q: Can one use an intuitive method (like the summng over topologies) to calculate the scattering amplitudes in M(Atrix) theory and Matrix string theory?

4. Q: How does Loop Quantum Gravity violate Lorentz Invariance?

A: A discrete spacetime => a Lor?entz-violating theory, since it means we have a particular aether, to take measurements wrt to etc., a preferred ref. frame/. Also, as LM has once explained, these discrete granules of spacetime cannot Lorentz contract, which also implies Lorentz-violation.

5. Q: How is the Holographic principle formulated mathematically? ,

6. Q: Why does one of the dimensions of F-Theory need to be a temporal one?

7. Q: What is the argument that Carlo Rovelli proposed to “prove” that LQG does not break Lorentz symmetry ? .

C: Something related to holography, which I don’t think LQG satisfies, so it’s probably wrong.

8. Q: Why are the Type II String Theories T-dual to each other ? .

A: If we have the GSO Projection for Type IIA or Type IIB as m $\mathcal{P}^+$, we see that under T-duality, since it negates the bosonic $X^\mu$, it should also negate the fermionic $\psi^\mu$ by worldsheet supersymmetry. Therefore, since this means that $\mathcal P^+$ # is changed to $\mathcal{P}^-$, the GSO Projection changes from chiral to non – chiral, and vice – versa .

9. Wait, I think you deleted my original question itself; I meant remove the part about the GSO projection only! .

10. Mark Mitchison says:

How do measurements in mutually unbiased bases relate to each other (pictorially) in the diagrammatic calculus of categorical quantum mechanics?

11. Mark Mitchison says:

Reference request: Current status of research on open quantum systems interacting with strongly correlated environments?

12. Mark Mitchison says:

What are the general conditions necessary for a Matrix Product State (MPS) solution to exist for the steady state of a one-dimensional non-equilibrium Lindblad models?

13. Mark Mitchison says:

Does an experimental procedure exist to measure two-time correlation functions of a two-level atom or spin qubit directly in the time domain (i.e. not by just measuring the power spectrum in linear response)?

• Mark Mitchison says:

Posted to see how experimental we are willing to go 🙂 As far as I know this is a research-level question, but obviously it’s about experimental physics…

14. Dilaton says:

How and why do tachyons reappear when building realistic models from superstring theory, which should be generally be free of tachyons? Does this always happen or only when trying to build certain specific models?

15. Dilaton says:

What is the mechanism of D-brane / anti-D-brane annihilation used for in early universe string cosmology? What effects does this help to explain?

16. Dilaton says:

What do the quantum Lorentz generators, needed to have a Lorentz invariant theory, look like in LQG if they can be constructed?

17. What was Acharya, Kumar, and Kane’s argument for the MSSM appearing in the FT limit of M-Theory G(2) compactifications?.

18. […] We already have started to gather example questions. […]

19. Dilaton says:

I think that such technical theoretical physics questions

http://physics.stackexchange.com/q/80272

should on the new site be more welcome than on Physics SE, where it was first ignored and now a rascal came along and even downvoted it …

This question will be automatically deleted due to very stupid settings of a script that deletes all questions, which have a (even only slightly) negative score, no answer, and are older than 30 days. So it would be nice if some people who think it is not deletion worthy too could save it by some upvotes and / or an answer (I am not able to do anything about it at present) …

20. Dilaton says:

Does quantum gravity and/or string/M-theory (which is really the same thing, at the end) allow us to interpret any physical phenomena as phenomena that take place in a well-defined geometric background? What’s the shape and topology of this background?