the unscience of the unparticle

ELASTIC “unparticles” could explain a mysterious signal glimpsed at a particle collider a year ago. That would link a tenuous but intriguing idea to one of the biggest mysteries in physics: why matter prevails over antimatter in the universe.

“I think this will increase the unparticle’s credibility as a theory,” says Run-Hui Li of Yonsei University in Seoul, South Korea, the leader of one of two teams proposing the link.

Matter and antimatter are thought to have been created in equal amounts after the big bang, yet something has caused matter to be far more dominant than antimatter, at least in our patch of the universe.

A possible explanation is that some physical processes favour matter. For example, according to the standard model of particle physics, particles known as B mesons constantly switch, or mix, between their matter and antimatter forms. Because it is slightly easier for an anti-B meson to become a normal B meson than vice versa, an imbalance accrues. This “uneven mixing” gets transferred to the particles produced when B mesons decay, but alone is not big enough to explain the observed matter-antimatter asymmetry.

Previously, several teams have glimpsed examples of asymmetry even larger than the standard model predicts. In May 2010, researchers at the Fermi National Accelerator Laboratory in Batavia, Illinois, reported a 1 per cent preference for the number of B mesons produced in their particle smasher, the Tevatron (arxiv.org/abs/1005.2757). This is 40 times larger than the imbalance predicted by the standard model.

Two separate groups now suggest an explanation for this larger asymmetry lies in the unparticle, a hypothetical entity conjured up in 2007 by theorist Howard Georgi of Harvard University. Georgi suggested that a property known as scale invariance – seen in fractal-like patterns that remain unchanged even when you zoom in and out to different scales, like the branching of redwood trees and the jagged edges of coastlines – could apply to individual particles too. The charge and spin of unparticles would be fixed but, counter-intuitively, their mass would somehow vary depending on the scale at which an observer viewed the particle.

Such unparticles could play a role in a popular proposed extension to the standard model, known as supersymmetry.

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