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Tuesday, 24 March 2015

Technicolor theory and the Higgs

Earlier this year, claims have been bouncing around the internet about the results of the biggest discovery in particle physics. That the Higgs boson, the boson meant to help us understand where the origin of mass in particles comes from, is not actually the Higgs boson and that Peter Higgs should have his Nobel Prize whisked away from him quicker than you can say ‘Large Hadron Collider’.

Photograph of the Compact Muon Solenoid (CMS) at CERN in Switzerland
The Compact Muon Solenoid (CMS) is one of the detectors in the Large Hadron Collider where the Higgs boson has been detected (the other is ATLAS). Data from this is processed by supercomputers which produce the beautiful collision diagrams for scientists to pore over and deduce what particles have been detected. Image credit: CMS/CERN

But surely the Nobel committee can’t have given away such a prestigious award so carelessly, without having checked the integrity of the results particle physicists have spent years working on? I spoke with Dr Alexander Belyaev from the University of Southampton, who explained how these articles have somewhat missed the point, and how it relates to his research into Technicolor theory. So what is a Higgs boson anyway?

The Higgs boson discovery of 2012 was undoubtedly the largest discovery in many areas of physics, providing answers to some long-standing questions. It was first proposed to exist by Peter Higgs in the 1960’s and came about from his theory of broken symmetry[1]. I won’t go into too much detail about that here but part of this theory explains in the simplest way (not that you’d believe it from looking at the equations) how particles get their mass. The process he describes is known as the Higgs mechanism, and the key to it is a particle called the Higgs boson.

You can think of the way the Higgs boson “works”, like this: imagine a room full of people who all know each other, and who want to talk to their friends. If you don’t know anybody, you may be able to pass through the room quickly, without interacting with anybody. But if you’re popular with this particular group of people, you’ll find your passage through the room slowed by constant interactions with the people you pass by. Each of the people in the room are acting as a Higgs boson - particles they don’t interact with, such as photons, can travel at the speed of light; but particles (including other Higgs bosons) that do interact are slowed down. This is what distinguishes particles that have mass (and a gravitational pull) from those that don’t.

Actually there is something like a Higgs mechanism reflected in many branches of particle physics; the standard model has a version, supersymmetry has its own version, even a relatively new theory called technicolor theory also requires a Higgs boson. These numerous theories all offer a way of describing the world on a sub-atomic scale, and there are ways in which each theory has it’s successes and it’s failures. Physicists do not yet know which model is correct, and debate over the nature of particles, including the Higgs boson, has arisen.

So the big question surrounding the Higgs is not whether we have discovered it or not, because of course we have. No, the question lies in which one? Dr Belyaev works on a branch of particle physics called technicolor theory, and hopes that his research will help answer this question.

Technicolor theory looks at particles which are much heavier than the particles in the standard model theory. It was developed as a way to provide alternative theories when the standard model predictions no longer worked.

In the rules of the standard model, the Higgs is an unstable particle and decays quickly into other smaller particles. When the Higgs was finally detected in the Large Hadron Collider it was found that the particles it decayed into were much heavier than we would expect them to be. Corrections were made, called quantum corrections, to account for this mismatch in size[2], but in Technicolor theory the numbers match up[3]. No fine tuning is needed in Technicolor theory, which is great because it means it’s much simpler than the standard model and therefore could be a good candidate for replacing it.

Much more data is needed before we can define which Higgs has been discovered. Currently the results have fairly large errors in them, though they are consistent enough for us to take some assumptions as correct (i.e. that we have found a Higgs).

We need a more powerful accelerator, says Dr Belyaev, maybe, a linear one which can be six times more accurate. I think this technology could be here in, say, 10 years from now.

With a more powerful collider, we would expect to see many more Higgs particles detected, and scientists could definitely say whether the Higgs is Technicolor, or if our maths is just all wrong. Currently the ATLAS and CMS detectors in the Large Hadron Collider are looking for evidence of the decay products which would be indicative of the Technicolor Higgs, but the detections are too few and far between for any real progress to be made.

Red, green and blue lights showing secondary colours.
Though quarks are not actually thought to be colourful, the red, green and blue analogy helps scientists to visualise what’s going on, hence the name ‘technicolor’. Image via Wikimedia Commons CC-BY-SA-3.0 

Before I left Dr Belyaev to his work, I asked him where the catchy name of this theory came from. Sadly, it’s not because the Higgs is a funk-soul disco-techie, but it’s more likely the name came from how people originally defined quarks in the late seventies. Each quark was given a colour – red, green and blue. The name Technicolor provided a way of differentiating the quarks from the original standard model quarks.

The point is, we need a new theory and I think Technicolor is the way forward. But yes, of course we have found the Higgs! We just don’t know which one.

Finding a unified way to describe the underlying mechanisms that govern the way particles interact with each other is a large part of understanding exactly how the physical world around us works. It is clear there is not enough information currently to convince ourselves that one particular theory is correct. Physicists like Dr Belyaev and his team work toward a future where we can accurately describe and understand these fundamental unknowns such as how particles get their mass.

This article was written by TWDK's physics editor Grace Mason-Garrett, with thanks to Dr Belyaev.

References
why don't all references have links?

[1] Higgs, Peter W. "Broken symmetries, massless particles and gauge fields." Physics Letters 12.2 (1964): 132-133. DOI: 10.1016/0031-9163(64)91136-9
[2] Casas, J. A., Espinosa, J. R., & Quirós, M. (1995). "Improved Higgs mass stability bound in the standard model and implications for supersymmetry." Physics Letters B, 342(1), 171-179.
[3] Arkani-Hamed, N., Cohen, A. G., Katz, E., & Nelson, A. E. (2002). "The littlest higgs." Journal of High Energy Physics, 2002(07), 034.