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Hi, I am a string theorist and a publicist.


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comment Spontaneous symmetry breaking and time-reversal symmetry
I would say Yes - but what is the cause and what is the consequence or a description is debatable... But generally Yes, states in different superselection sectors have "very different" macroscopic consequences for the environment, so the information about the superselection sectors is being copied as classical information as these states decohere - so decoherence is why the separation to the sectors becomes visible.
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29
comment Polchinski Equation (10.4.7)
Similarly, the OPE you are asking for is not "equal" to zero, but it is $\sim 0$ because the OPEs had no singular terms to start with, so one couldn't have gotten any singular terms by differentiation, either. But again, $b(\sigma_1) \partial_\sigma^7 b(\sigma_1) b(\sigma_2)c(\sigma_2)$ has no reason to be zero, has it?
Jul
29
comment Polchinski Equation (10.4.7)
You are probably confused by the difference between the $=$ sign in the OPEs, and the sim sign $\sim$. The latter indicates that the right hand side only lists the singular terms, i.e. is correct up to additive terms $+O(1)$.
Jul
29
comment Polchinski Equation (10.4.7)
Dear MaPo, the product of the two operators is surely not equal to zero. Just map it to the cylinder, if the plane distracts you. $b(\sigma_1) b(\sigma_2)$ is just a product of two anticommuting operators, right? Why should it be zero? It is $O(z)$ indeed because there's no singularity for $z\to 0$ and the value for $z=0$ is zero due to anticommutation. But for $z\neq 0$, it cannot be zero.
Jul
28
comment Graviton saturation, alternative explanation of galaxy rotation curves?
Magnus, you would need to write some equations. This kind of "spirit" of yours is nice, and probably basically shared by some original minds, but what is missing are the equations - what actually makes the gravity bounded and how? Moreover, what you need is kind of the opposite. You need to make gravity stronger than expected by Newton when the acceleration is too low (MOND) etc. At this vague level, this fixed theory of yours is pretty much "the same thing" as MOND, and if you mean something else, you need to describe it more accurately than you did.
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revised Polchinski Equation (10.4.7)
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answered Polchinski Equation (10.4.7)
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comment Connection between the M5 brane and (2, 0) superconformal field theory
Also, there is no contradiction between the non-existence of a Lagrangian of a full theory, and the existence of a Lagrangian for a dimensionally reduced (compactified, taken to the limit) theory. And yes, the behavior of M5-branes must have some more contrived, bootstrap-like, cubic and higher-order etc. structures that are seeds of those in all of M-theory. There are some hints in the literature, but no complete answer. Each paper about (2,0), and there are lots of them, addresses these questions to one extent or another but there's no known complete answer.
Jul
28
comment Connection between the M5 brane and (2, 0) superconformal field theory
This is a very interesting question with lots of dimensions and subtleties and implicit errors in the question etc. First of all, (2,0) is just the low energy, deep infrared limit of the dynamics of coincident M5-branes, not "everything" about M5-branes in a generic situation. Second, the non-existence of a Lagrangian description is a conjecture, or a claim about the invalidity of the usual simplest Lagrangians we could guess. The problem is with the self-duality of the 3-form.
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