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Nov
6
comment Why do three dimensional gauge theories flow to conformal theories in the infrared?
You're right about the dimensionality and Lorentz invariance, I edited this in. It doesn't have to be weak coupling, as long as you assume that scale invariance implies conformal invariance. It doesn't have to be massless, and it's almost always not.
Nov
6
comment Why do three dimensional gauge theories flow to conformal theories in the infrared?
(To clarify, it is the assumptions that are weak and not the authors.)
Nov
6
answered Why do three dimensional gauge theories flow to conformal theories in the infrared?
Nov
5
comment Ghosts on Torus worldsheet
It would be hard to explain it better than chapter 5 of Polchinski. I would recommend that to you.
Nov
5
answered Ghosts on Torus worldsheet
Aug
23
comment Generalisations of AdS/CFT with string theory on both sides
Why do you say that T-duality is holographic?
Aug
11
revised Why is it hard to give a lattice definition of string theory?
added 38 characters in body
Aug
11
asked Why is it hard to give a lattice definition of string theory?
Aug
11
answered How to obtain the constant $a^g$ in Eq.(2.7.19) in Polchinski's string theory book
Aug
9
awarded  Yearling
Aug
6
awarded  Enthusiast
Aug
4
asked Peierls Argument for Absence of Long Range Order
Aug
2
comment How are low energy effective actions derived in string theory?
That's right, the two are equivalent. I think you should be able to understand the effective action by reading Polchinski, but that paper by Callan etc. might help also.
Aug
1
comment Mass of empty AdS$_5$
You sure would, and it's in fact done in that paper.
Jul
31
comment Mass of empty AdS$_5$
Your expression is correct, see Balasubramanian and Kraus arxiv.org/abs/hep-th/9902121. @MattReece your argument would hold in Poincare coordinates, but AdS in global coordinates is dual to a CFT on $S^3\times R$. This has a vacuum energy from the Casimir effect, as explained in the above reference. This is familiar from 2d CFT, where the Hamiltonian on the cylinder is the dilatation operator plus a shift proportional to the central charge.
Jul
31
revised How are low energy effective actions derived in string theory?
deleted 101 characters in body
Jul
31
revised How are low energy effective actions derived in string theory?
added 101 characters in body
Jul
31
revised How are low energy effective actions derived in string theory?
added 246 characters in body
Jul
31
answered How are low energy effective actions derived in string theory?
Jul
31
comment How are low energy effective actions derived in string theory?
You just have to compute a lot of string amplitudes, which Polchinski doesn't want to waste time doing. Some of these are left as exercises. Once you've done this you can look for an effective field theory that reproduces the amplitudes, and you'll find supergravity. Alternatively, once you've convinced yourself that string theory preserves spacetime supersymmetry, you know from the fact that there aren't very many consistent supergravity theories that you're going to get the right answer.