When axions strike

Published in New Scientist, 11 Nov 2015

Our best models can’t explain why the mass-giving Higgs boson is so small. Resurrecting a 40-year-old idea could put this riddle and two others to rest

TO MOST of us the mass of an eyelash seems like just about nothing. But to a Higgs boson – the particle believed to endow all others with their mass – it might as well weigh a tonne. The mass of the Higgs has a bearing on all the other particles that make up reality, and if it were as large as an eyelash the world would look very different. The electrons buzzing inside your computer’s circuits would be as weighty as the dust coating the top of it. If the dust bulked up on the same scale, each speck would have roughly the mass of a well-fed elephant.

A strange world indeed. Yet believe the standard model, our best theory of particle physics, and this is just the sort of situation we should expect to find ourselves in. According to this idea, the Higgs should be roughly the mass of an eyelash. This is so big that it would produce fundamental particles almost so massive and dense that they would create a microscopic black hole every time they collided.

Yet none of the fundamental particles – electrons, quarks, neutrinos and so on – are anywhere near the mass they ought to be. They’re all much smaller: 100 quadrillion times smaller.

Why the clustering at the bottom? This “hierarchy problem” has haunted physicists for decades, and there’s never been an easy answer. The front runner, a theory known as supersymmetry, has fallen from grace now that the Large Hadron Collider (LHC), located near Geneva, Switzerland, has searched the most obvious avenues for evidence and failed to find it.

We’re desperate for a way to explain this puzzle. But perhaps the answer has been under our noses all along. According to a trio of physicists with a grand idea, a single particle known as the axion, a plaything of theorists since the 1970s, makes the problem disappear in a flash – and fixes a couple of other mysteries on the side. […]

The rest of this article is available here.