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seen Dec 18 at 22:16

I am a postdoc in mathematics, but have my degree in theoretical physics. My work is about mathematical structures motivated from quantum field theory and string theory. For more see here.


Aug
22
comment experimental bounds on microcausality violation
@Ben, that's of course a good point. Somehow I was hoping for something fancier, but I guess you must be right.
Aug
22
asked experimental bounds on microcausality violation
Aug
20
answered The Chern-Simons/WZW correspondence
Aug
13
revised Obtaining supergravity from gauging global supersymmetry
fixed grammar and fine-tuned somebody else's edit that highlights that the last citation is a self-citation
Aug
10
comment Obtaining supergravity from gauging global supersymmetry
But apart from their role as higher gauge groups under which higher branes are charged, higher Lie groups also appear as "higher orbispace" target spaces on which higher branes may propagate. This is the second role mentioned in the above reply. For instance the supergravity Lie 3-algebra is also the target "higher super-orbispace" which is such that a sigma-model map into is a combination of a map to spacetime and a 2-form on the worldvolume. This way it serves as a higher geometric target space that renders the 5-brane a genuine, albeit "higher" sigma model.
Aug
10
comment Obtaining supergravity from gauging global supersymmetry
... next up the ladder is the circle 3-group $\mathbf{B}^2 U(1)$. A gauge field for this is a $C$-field ncatlab.org/nlab/show/supergravity+C-field and this couples analogously to the membrane = 2-brane. In fact, in both these cases really the circle $n$-group is just one component of a more complicated nonabelian higher group. For instance the circle 2-group is part of what is called the "String 2-group" ncatlab.org/nlab/show/string+2-group and its variant the "String^c 2-group" ncatlab.org/nlab/show/string%5Ec+2-group. A gauge field for this is twisted heterotic B-field.
Aug
10
comment Obtaining supergravity from gauging global supersymmetry
Yes, Lie $n$-algebras and their Lie $n$-groups correspond to Lie algebras and Lie groups as $(n-1)$-branes correspond to 0-branes = point particles. The easiest example is the circle 2-group ncatlab.org/nlab/show/circle+n-group $\mathbf{B}U(1)$. A gauge field for this 2-group is a B-field ncatlab.org/nlab/show/Kalb-Ramond+field and this couples to a string = 1-brane in direct anlogy of how a $U(1)$-gauge field couples to a point particle = 0-brane (by what is called the "WZW term" ncatlab.org/nlab/show/Wess-Zumino-Witten+model). Next up the ladder is...
Aug
10
answered Obtaining supergravity from gauging global supersymmetry
Aug
10
comment Gauge invariant Chern-Simons Lagrangian
This nice argument of course requires that the 3-manifold we are interested in is "co-bounding" (the boundary of a 4-manifold) in the first place. Depending on which extra structure one has (e.g. spin structure etc.) this is not always the case. But the good message is that essentially this argument goes through fully generally if one refines it "locally" as expressed in the language of stacks. An exposition of this is at the beginning of this article: ncatlab.org/schreiber/show/…
Aug
9
comment The Role of Rigor
You haven't seen clarity yet.
Aug
9
revised What is kappa symmetry?
edited body
Aug
9
answered What is kappa symmetry?
Aug
5
comment Is string theory a quantum theory of gravity?
The distinction between "postdiction" and "prediction" is not interesting. For instance, suppose tomorrow somebody solves the mass gap problem for Yang-Mills theory. Then we won't say "QFT postdicts the mass gap of Yang-Mills", just because we knew it already from experiment and numerics. Instead we will say "QFT explains the mass gap of Yang-Mills in that it derives it from simpler axioms". And this is true also about how string theory yields gravity.
Aug
5
comment Is string theory a quantum theory of gravity?
(Not to mention that via AdS/CFT supposedly properties of quantum black holes are encoded in the dynamics of a sYM CFT on an asymptotic boundary of spacetime.)
Aug
5
comment Is string theory a quantum theory of gravity?
It is not true that perturbative string theory says nothing about black hole singularities, because of "the existence of a classical spacetime". Instead, it knows about all properties of such black holes that are "protected" by supersymmetry (and these are more than for plain supersymmetric back holes). This works by following a weakly coupled configuration of branes (gravity back reaction approximately turned off) as the coupling constant is turned on. All the detailed microscopic computations of BH entropy work this way ncatlab.org/nlab/show/black+holes+in+string+theory .
Aug
5
comment Is string theory a quantum theory of gravity?
The starting point of perturbative string theory is not an "unmotivated and unexplainable assumption about the nature of particles". Instead, it's a natural variation of the perturbative description in QFT. It may be physically wrong, but it is by no means unmotivated and unexplainable. Here it helps to remember the "worldline formalism" for QFT ncatlab.org/nlab/show/worldline+formalism . If you can see this and not naturally wonder if there could be a higher dimensional worldvolume generalization of this formalism, you have to return your theoretical physics license ;-)
Jul
30
awarded  Nice Answer
Jul
16
comment On the Coulomb branch of N=2 supersymmetric gauge theory
@user6818: decent explanation of these phenomena is in lecture 14 of part IV around p. 1334 of the second part of the collection "Quantum Field and Strings" ncatlab.org/nlab/show/Quantum+Fields+and+Strings . (Notice that despite the subtitle "A course for mathematicians" this is not in fact a course for mathematicsians, but for physicists who are looking for genuine understanding.)
Jul
15
comment About the stability of the ground state of the bosonic string
I wouldn't say so. Also the closed string tachyon condensation has been studied with avail, and better understood, if admittedly less so than the open string tachyon. A list of references is here ncatlab.org/nlab/show/tachyon#ReferencesInStringTheory .
Jul
14
revised About the stability of the ground state of the bosonic string
added 4 characters in body