Monday, December 31, 2012

Gravito-Weak Unification?

A new preprint submitted earlier this month by a group of authors including one of the leading loop quantum gravity scholars suggests a deep link between gravity and the fact that the weak force acts only on left parity particles.  Gravitational origin of the weak interaction's chirality Stephon Alexander, Antonino Marciano, Lee Smolin (Submitted on 20 Dec 2012)
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.
21 pages 
The conceptual connection is particularly attractive because fundamental particle mass is deeply linked to weak force interactions.  All massive fundamental particles interact weakly, all fundamental particles that lack rest mass do not interact weakly, and the Higgs boson often described as the source of fundamental particle mass is at the heart of electro-weak unification.  It would make sense if interial mass via the Higgs field and gravitational mass, which general relativity states is equivalent to intertial mass, have a deep common source.

The unification apparently gives rise to a sterile neutrino which is an analog to the Higgs boson in the gravitational sector, and a U(1) field that acts on the dark matter sector.

Now, to be clear, this is just a theoretical Beyond the Standard Model (BSM) notion that someone is putting out there, like hundreds of other papers by theoretical physicists (if not thousands) each year, no one is claiming that it is the truth, just that the truth about Nature could conceivably look something like this.  What makes it notable is that I've never seen a BSM theory taking this approach before - it is exploring relatively virgin theoretical territory at a time when the more well trodden paths of BSM theories are increasingly looking like dead ends in light of new experimental data.



Maju said...

I don't understand much but for what you say it seems intriguingly plausible and suggestive of logical coherence. Even if incorrect, being a novel approach, it may well open the eyes of other researchers to novel approaches.

Nice finding, thanks.

andrew said...

A similar paper was written in 2008: