I'm curious as to something I read on Berkeley's website. Does anyone happen to know why, according to this model,right hand neutrinos are unaffected by all forces except gravity?
(Model taken from http://ctp.berkeley.edu/neutrino/neutrino5.html)
An alternative way to make right-handed neutrinos extremely weakly interacting was proposed in 1998 by Nima Arkani-Hamed at the Stanford Linear Accelerator Center, Savas Dimopoulous of Stanford University, Gia Dvali of the International Centre for Theoretical Physics in Trieste and John March-Russell of CERN. They exploited an idea from superstring theory in which the three dimensions of space with which we are familiar are embedded in 10- or 11-dimensional spacetime. Like us, all the particles of the Standard Model — electrons, quarks, left-handed neutrinos, the Higgs boson and so on — are stuck on a three-dimensional "sheet" called a three-brane.
One special property of right-handed neutrinos is that they do not feel the electromagnetic force, or the strong and weak forces. Arkani-Hamed and collaborators argued that righthanded neutrinos are not trapped on the three-brane in the same way that we are, rather they can move in the extra dimensions. This mechanism explains why we have never observed a right-handed neutrino and why their interactions with other particles in the Standard Model are extremely weak. The upshot of this approach is that neutrino masses can be very small.