Can Gravity be Described by the Square of the Strong Force?

[cuallito]

I remember reading some stuff online (it *seemed* legit) about how some physicists were getting finite answers to graviton scattering amplitudes by computing associated QCD diagrams and "squaring" the result. Does this sound familiar to anyone?

 

[Simon Bridge]

That sounds like a garbled description of:
http://www.scientificamerican.com/article/search-for-new-physics/

 

[atyy]

http://arxiv.org/abs/1004.0693
Gravity as the Square of Gauge Theory
Zvi Bern, Tristan Dennen, Yu-tin Huang, Michael Kiermaier

 

[blakej]

sounds similar to a theory I saw on some science show where the theorist was saying that gravity may be a different manifestation of the strong force with its force carrier being two gluons

 

[ohwilleke]

Of course, there are also theories of gravito-weak unification, such as Stephon Alexander, Antonino Marciano, and Lee Smolin "Gravitational origin of the weak interaction's chirality" (January 7, 2014). http://arxiv.org/abs/1212.5246

We present a new unification of the electro-weak and gravitational interactions based on the joining the weak SU(2) gauge fields with the left handed part of the space-time connection, into a single gauge field valued in the complexification of the local Lorentz group. Hence, the weak interactions emerge as the right handed chiral half of the space-time connection, which explains the chirality of the weak interaction. This is possible, because, as shown by Plebanski, Ashtekar, and others, the other chiral half of the space-time connection is enough to code the dynamics of the gravitational degrees of freedom.

This unification is achieved within an extension of the Plebanski action previously proposed by one of us. The theory has two phases. A parity symmetric phase yields, as shown by Speziale, a bi-metric theory with eight degrees of freedom: the massless graviton, a massive spin two field and a scalar ghost. Because of the latter this phase is unstable. Parity is broken in a stable phase where the eight degrees of freedom arrange themselves as the massless graviton coupled to an SU(2) triplet of chirally coupled Yang-Mills fields. It is also shown that under this breaking a Dirac fermion expresses itself as a chiral neutrino paired with a scalar field with the quantum numbers of the Higgs.

Basically, this gives you a Standard Model electro-weak sector, a massless graviton, a Higgs boson and field shared by both the SM and gravitational sector, and a singlet sterile neutrino dark matter candidate that could have spin-1/2 or spin-3/2 as a gravitino without the other SUSY particles. It also ties the Higgs field role in generating mass more tightly to gravity's fundamental connection to mass.

On the other hand, QCD and gravity do have important similarities, such as the fact that they are non-abelian, because their force carriers have important self-interactions, and because they are non-renormalizable using QFT techniques in many phenomenologically important circumstances. Alexandre Deur, who comes from a QCD background has applied conclusions of QCD by analogy to argue to GR formulated at a graviton level gives rise to a Yukawa potential similar to that seen in QCD in addition to the ordinary gravitational potential in highly massive systems in which the matter-energy fields are not spherically symmetric. See, e.g., http://arxiv.org/abs/1407.7496 He proposed that these self-interaction effects which are overlooked when one tries to simplify the equations of GR in a spherically symmetric way as one often does, give rise to the phenomena attributed to dark matter. In that case, we don't need non-SM particles other than the graviton to explain all observed phenomena (except inflation and perhaps dark energy).

 

[Simon Bridge]

Hmm... is this another manifestation of how it is always possible to unify any three of the four forces, but the result leaves the fourth outside? Or something... I used to have notes on that... somewhere...