Dark forces from extended supersymmetryPresentation Transcript
Dark forces from extended supersymmetry Mitchell Porter presented at University of Queensland 10 November 2011
In supersymmetry, fermions are paired with bosons.
For example, the spin-2 graviton is paired with the spin-3/2 gravitino, which is a candidate for the dark matter.
In extended supersymmetry, particles have multiple superpartners.
Since there is about three times as much dark energy as there is dark matter, one might look for an N=4 or N=8 supergravity in which ¼ of the gravitinos are dark matter and ¾ of the gravitinos are dark energy.
I have no such model. But there is an old proposal for particle physics in which the gravitinos are naturally divided into a set of two and a set of six. This is Gell-Mann’s 1983 proposal for N=8 supergravity.
To realize Gell-Mann’s proposal, first we work in a space with negative cosmological constant (AdS4). N=8 supergravity has SU(8) x SO(8) symmetry there.
Then we break the symmetry to SU(3) x U(1).
48 of the 56 spin-1/2 fermions end up in representations that can be assembled into the quarks and leptons.
The proposal has some problems. For example, the weak force is not directly accounted for. Also, the masses are wrong!
But we are in a space of the wrong curvature anyway. We need asymptotically de Sitter space, not anti-de-Sitter space, to match the real world.
We need some extra positive energy density, to uplift to de Sitter space. What about the gravitinos?
As it turns out, under SU(3) the N=8 gravitinos fall into two groups. Two are “singlets”, the other six are “triplets” or “antitriplets”.
Also, the eight unused spin-1/2 fermions have the same SU(3) transformation properties as the gravitinos. They are “goldstone fermions” that are absorbed by the gravitinos and give them mass.
You now know as much as I do. I still have no model, but the path ahead is clear…
Look for a solution to N=8 supergravity with the following characteristics:
It is a de Sitter uplift of the SU(3) x U(1) critical point.
Dark energy comes from a condensate of SU(3)-triplet gravitinos.
Dark matter comes from the remaining SU(3)-singlet gravitinos.
Now I will describe where these ideas actually came from.
In 2005, Bilson-Thompson proposed to identify the quarks and leptons with braids. He had no equation, just an idea.
In 2010, Marni Sheppeard noticed that there were some unused braids, the reflections of the neutrino braids. She called them “mirror neutrinos”.
Sheppeard and her collaborators are trying to devise a whole new framework for physics using the extended braid set. A condensate of mirror neutrinos will be responsible for gravity and for mass.
Cosmologically, they use the ideas of Louise Riofrio, who predicts 9/4 π for the dark energy fraction and 3/4 π for the dark matter fraction. Sheppeard wants to get the 1/4 π factor from recent “holographic” calculations of viscosity of plasmas in strongly coupled field theories.
So it’s all rather unorthodox.
Nonetheless, it was during a search for a model realizing the Riofrio-Sheppeard theory of the dark sector, that I unearthed Gell-Mann’s proposal.
Sheppeard’s mirror neutrinos correspond to the SU(3)-(anti)triplet goldstone fermions in Gell-Mann’s proposal, the ones that give mass to the “dark energy gravitinos”.
There are many other aspects to the possible mapping between Sheppeard et al and Gell-Mann 1983, but they are somewhat technical and uncertain.
So to sum up, we have, not just a new approach to the physics of the dark sector, but the possibility that N=8 supergravity has a radically different description in terms of quantum braids.
I used to say that dark cosmology offered no real guidance to particle physics, because there was too little data. I won’t say that again!