New Particles and Epicycles

PhysicsWeb has a story about a new theory of axions that claims to resolve some discrepancies between past experiments. Two previous experiments looking for axions– hypothetical weakly interacting particles that might be an explanation for dark matter– have found conflicting results: the CAST experiment looking for axions produced in the Sun found nothing, while the PVLAS experiment looking for axions by studying the rotation of polarized light in a magnetic field may have seen something. (I talked a bit about the latter here.)

Of course, the new theory is not without its complications:

Now, Rabi Mohapatra from the University of Maryland and Salah Nasri from the University of Florida say that the two results can be reconciled if one considers the source of the axions. Whereas in the PVLAS experiment axions would have been produced locally in the laser beam at room temperature or colder, the CAST experiment was monitoring axions produced in the Sun’s core at about 10 million degrees Celsius.

Mohapatra’s theory is that a phase transition could occur at Sun’s high temperatures that destroys the coupling altogether, rather like a magnet losing its magnetism when heated. This would account for the null findings of CAST. However, this theory would also require a new particle – a force-carrying boson with a mass of about 100 MeV – to account for the coupling observed in PVLAS. Although such a particle has not been seen, Mohapatra says that it could be sought in future experiments involving the decay of upsilon particles.

I’m just not crazy about the idea of resolving a discrepancy between two experiments looking for a hypothetical particle that nobody has conclusively seen by introducing yet another hypothetical particle that nobody has seen. As I said before, I don’t think that Occam’s Razor is a decisive principle in science, but I’d really like to think that there might be a simpler explanation than that. There are lots of problems that can be fixed if you just posit new particles and forces, but at some point, you’re just accumulating epicycles, and need to start over.