Synopsis

Particle Families Come in Three

Physics 5, s68
The existence of three families of fundamental particles may result from our universe behaving like a topological insulator, according to a theoretical proposal.

The fundamental fermions belong to three families, but physicists don’t know why there aren’t more. A new theory presented in Physical Review Letters imagines that our universe has an extra spatial dimension that is “off-limits” to particles in a similar way that the interior of materials called topological insulators is off-limits to conducting fermions. This geometrically based formulation could naturally produce three families, and may make testable predictions about neutrinos and the Higgs boson.

Each family in the standard model of particle physics includes four members. The lightest family, for example, consists of the electron, the electron neutrino, the up quark, and the down quark. The other two families are progressively more massive. Nothing in the standard model rules out more families at higher and higher mass, but experimental evidence suggests that three is all there is.

As a way to explain this family tree, David Kaplan and Sichun Sun at the Institute for Nuclear Theory in Seattle, Washington, borrow an idea from condensed-matter physics and assume that spacetime resembles a topological insulator. These unique materials are insulators on the inside, but with free fermions conducting along the outer surface. By assuming a certain topology within an analogous, higher dimensional “insulator,” the authors can produce exactly three families of particles confined to the four-dimensional surface. Specific particle properties in the standard model, such as masses and couplings, could be the result of how these wave functions extend a small distance into the hidden extra dimension. – Michael Schirber


Subject Areas

Particles and FieldsTopological Insulators

Related Articles

Sterile Neutrino Down but Not Completely Out
Particles and Fields

Sterile Neutrino Down but Not Completely Out

Neutrino experiments place the most stringent limits to date on a hypothetical fourth neutrino, but the possibility that such a particle exists remains open. Read More »

Powdering Up for Neutrinos
Particles and Fields

Powdering Up for Neutrinos

The search for neutrinos from past supernovae is getting an upgrade as Japan’s Super-Kamiokande experiment begins adding gadolinium powder to its giant water-based detector. Read More »

Electron Accelerator Recycles Energy for a Brighter Beam
Particles and Fields

Electron Accelerator Recycles Energy for a Brighter Beam

A test electron accelerator reuses the energy of the particles in order to achieve a brighter beam without drawing more power from the grid. Read More »

More Articles