Types of quantum field thories
FQFT and cohomology
SYM is an SCFT.
Among all gauge theory Lagrangians that of , SYM is special in several ways, in particular of course in that it is conformally invariant and in that it has maximal supersymmetry; and ultimately by the fact that it is the KK-reduction of the very special 6d (2,0)-superconformal QFT and related by AdS7-CFT6 duality to the very special theory of 11-dimensional supergravity/M-theory.
Accordingly, it is to be expected that the quantum observables of , SYM satisfy special relations that make them more tractable than the observables of a generic gauge theory, in particular by having closed-form expressions. Indeed, such relations have been and are being uncovered in the last years, in particular in what is called the planar limit of the theory, where scattering amplitudes are dominated by Feynman diagrams that can be given the structure of planar graphs.
This includes notably the following phenomena:
The operator spectrum of the dilatation operator (the part of the stress-energy tensor which induces conformal transformations) can be expressed in closed form, indeed when regarded as a Hamiltonian it defines an integrable system equivalent to spin chain? models. This has been used in particular to explicitly check aspects of the conjectured AdS-CFT duality of , SYM with type II string theory on anti de Sitter spacetimes. See the review (Beisert et al).
Certain scattering amplitudes called maximally helicity violating amplitudes (“MHV amplitudes”) simplify drastically as compared to the generic situation and in fact are controled by a certain twistor string theory whose target space is a twistor space. See (Monteiro) for a review.
Such “exact solutions” of the theory are of interest in that even though N=4, D=4 SYM is very different from phenomenologically viable models such that QCD in the standard model of particle physics in that it is highly (super-)symmetric and conformal, it is still similar enough (being a nonabelian gauge theory minimally coupled to fermions) that one can or can hope to deduce from these exact results approximate information about these less symmetric theories.
In other words, because understanding observables in QCD/Yang-Mills theory in general is difficult, going to special points in the space of all such theories – such as the point of N=4, D=4 SYM – may be hoped to yield a tractable approximation. For more on this way of studying QCD and other realistic theories by studying instead their highly symmetric but phenomenologically unrealistic siblings, see also at string theory results applied elsewhere.
|brane||in supergravity||charged under gauge field||has worldvolume theory|
|black brane||supergravity||higher gauge field||SCFT|
|D-brane||type II||RR-field||super Yang-Mills theory|
|D0-brane||BFSS matrix model|
|D4-brane||D=5 super Yang-Mills theory with Khovanov homology observables|
|D1-brane||2d CFT with BH entropy|
|D3-brane||N=4 D=4 super Yang-Mills theory|
|NS-brane||type I, II, heterotic||circle n-connection|
|NS5-brane||B6-field||little string theory|
|M-brane||11D SuGra/M-theory||circle n-connection|
|M2-brane||C3-field||ABJM theory, BLG model|
|M5-brane||C6-field||6d (2,0)-superconformal QFT|
|topological M2-brane||topological M-theory||C3-field on G2-manifold|
|topological M5-brane||C6-field on G2-manifold|
An introduction to SYM is in
More recent results are in
Superconformal invariance of , SYM can be shown with the result of
(after regarding it as SYM with three adjoint chiral superfield?s).
A comprehensive discussion of the integrability related to anomalous dimension in the planar sector is in
A review of MHV amplitudes is in
Discussion of special properties of scattering amplitudes in the planar sector is in
For mathematical background see
For the moment see at
and also at