Talk:N = 8 supergravity

N=8 Supergravity is the most symmetric quantum field theory which involves gravity and a finite number of fields. It can be found from a dimensional reduction of 11D supergravity by making the size of 7 of the dimensions go to zero. It has 8 supersymetries which is the most any gravitational theory can have since there are 8 half-steps between spin 2 and spin -2. (A graviton has the highest spin in this theory which is a spin 2 particle). More supersymmetries would mean the particles would have superpartners with spins higher than 2. The only theories with spins higher than 2 which are consistent involve an infinite number of particles (such as String Theory). Stephen Hawking in his Brief History of Time speculated that this theory could be the Theory of Everything. However in later years this was abandoned in favour of String Theory. There has been renewed interest in the 21st century with the possibility that this theory may be finite.

Calculations
It has been found recently that the expansion of N=8 Supergravity in terms of Feynman diagrams has shown that N=8 Supergravity is in some ways a product of two N=4 super Yang-Mills theries. This is written schematically as:

N=8 Supergravity = (N=4 Super Yang-Mills) × (N=4 Super Yang-Mills)

Particle Content
The theory contains 1 graviton (spin 2), 8 gravitinos (spin 3/2), 28 vector bosons (spin 1), 56 fermions (spin 1/2), 36 scalar fields (spin 0) where we don't distinguish particles with negative spin. These numbers are simple combinatorial numbers that come from Pascal's Triangle.

One reason why the theory was abandoned was that the 28 vector bosons which form an O(8) gauge group is too small to contain the standard model U(1)xSU(2)xSU(3) gauge group which can only fit within O(10).

For model building has been assumed that almost all the supersymmetries would be broken in nature leaving just 1 supersymmetry (N=1) although now days because of the lack of evidence for N=1 supersymmetry higher supersymmetries are now being considered such as N=2.

clarification needed
"This is not so surprising as N=8 supergravity contains 6 independent representations of N=4 Super Yang–Mills."

this is not explained well. 192.235.78.16 (talk) 08:18, 30 March 2014 (UTC)