The most shocking outgrowth of the physics of branes has been the Maldacena conjecture. This conjecture states that M-theory subject to particular boundary conditions is in fact equivalent to some supersymmetric Yang-Mills theory on a manifold of smaller dimension. One example is the so-called AdS/CFT correspondence, in which string theory with boundary conditions matching the ten-dimensional manifold given by the product of 4+1 Anti-DeSitter space and a five-sphere (AdSsub5 x S^5) is conjectured to be equivalent to 3+1-dimensional super Yang-Mills theory.
The concepts involved in LQFT simply discribe what makes up these small structures themselves and in essence discribe how the String, that is the particle as an extended object, is formed.
Part of the question being asked is what is the most fundamental part of nature? Is it the String, the Branes, or the Loops?
In addition to strings, M-theory contains a zoo of higher dimensional objects; e.g. 2-dimensional membranes (aka 2-branes), 3-dimensional `3-branes', etc. An object with p spatial dimensions is known as a p-brane. These branes are now thought to be as fundamental as the string itself. The various branes are related to fundamental strings by powerful symmetries known as dualities.
The branes can form up into Strings and Strings can also form up into branes, but both objects are composed of something more primary themselves. Take String and one can weave a fabric which well term a brane or sheet. Yet, that same sheet can be decomposed into its basic string which in turn can be decomposed into its basic fabric parts itself.
If the quantum loops are actually the basic fabric then they could be seen as the most basic parts to be found in nature. However, at the present this has yet to be fully worked out or proven. Also any solid quantum theory will have to also account for where these basic bits of fabric actually came from. So a deeper fundamental question one can start with is Loops of what?
A starting point might be concentrating on the coupling constant issues. For example, the beta function has been calculated to four loops, in QED and in general matter flavor QCD/SQCD or SU(N_c). But even in QED, where Abelian Ward identities cancel divergences of wave function and vertex leaving only vacuum polarization logs, that doesn't tell you what "the running coupling" does at high orders. But the fact that this coupling exists can cause us to ask the question of coupling of what or to what?
We need to decide whether we're talking about a physical coupling, related to an amplitude, with the entire loop correction amplitudes resummed gauge invariantly; or an unphysical parameter in perturbative expansion in some particular renormalization scheme, perhaps in an asymptotic approximation that keeps only leading logs at high momentum. Also, we can have spacelike or timelike momentum transfer, depending on the physical process, and the subleading momentum terms depend on that.
But one could start this process of questioning by focusing on spacelike and timelike momentum transfer. In general with momentum we have energy coupling from one point to another. Coupling tends to imply direction to this energy flow which in turn implies a tensor field at play. But we can also have a simulation of a tensor field’s end product of direction via differences in a scalar field like the measurement of temperature. Under entropy we have flow of energy from a high temperature region into a lower temperature region. The result is a net coupling of energy from one region to another defined by tensor and scalar fields interacting.
This then sort of implies a picture where the basic building blocks of the cosmos are bits of energy. But then we have to further define exactly what energy is.
We measure energy via time, movement, etc in units expressing work. But then using time we are somewhat rather forced right back to a system with one of the original parts of the background invoked again when the whole idea was to get away from the background and form a background independent model.
Might seem a long way to bring up a point and indeed it is a long fashion to do so. But what is being shown here is that its hard to answer a question about the origin of something who’s very nature depends upon the background of time and space itself and who’s origin point would seem to be beyond some predetermined T=0 point.
