26 July 2006

Ghostly photons, axions or noncommutativity?

In March the PVLAS collaboration in Italy found a small polarization rotation when a laser beam went through a region with a large magnetic field. See here. The result can be interpreted as photons turning into axions, a still unobserved particle associated with the conservation of CP symmetry in strong interactions. Axions have no electric charge, a very small mass, and interact very weakly through the strong and weak forces. A very difficult guy to be detected!

Now DESY is planning an experiment using the FLASH, a machine which produces an extremely bright laser beam. The laser will go through a region with intense magnetic field and will be stopped by a wall. In the magnetic field some photons will turn into axions, like in the PVLAS experiment, pass through the wall, and another magnetic field on the other side of the wall will turn these axions back to photons. So photons will apparently come through the wall like ghosts (not the Faddeev-Popov ones!). Very clever! The proposal is here. They are planning to start the experiment by the end of 2006.

If the effect is real and if no axions are found an alternative explanation could be noncommutativity. A noncommutative photon acquires a phase in an electromagnetic background. This causes a rotation in the polarization as observed in PVLAS collaboration. In the DESY experiment no photons would be observed through the wall. That would be great!


Davi said...

Dear Victor,

Thanks for the news on the DESY experiment and for the link to the Chaichian et al's paper. I knew there was a paper on axions and NC and I was about to search for it for my thesis.

NC electrodynamics still has many problems, but perhaps experiments like this can shade some light on how to approach it.

Best regards,

Matti Pitkanen said...

PVLAS experiments is not consistent with axion interpretation. Personally I see axion as an ad hoc attempt to resolve the CP problem of QCD. The rate of rotation for polarization direction is by a factor about 2.8*10^4 too large for axion interpretation to work.

I have just constructed a TGD based model explaining the effect. TGD does not predict axion nor large CP breaking but it predicts a hierarchy of scaled variants of QCD. Axion is replaced by a scaled down variant of pion with mass of about 1 meV for which interaction Lagrangian with photons has the same form as for axions.

The model relates the mass about 1 meV of this exotic pion to the strength of the magnetic field used and explains also the rate for the rotation of polarization direction. The model also predicts that the effect is very sensitive to the ratio of the frequency of photon and the cyclotron frequency of electron in the magnetic field used. The TGD based model for quantum biology suggests that this ratio should be very near to 2^(k11), k=1,2,... and indeed equals to 2^(11) in the reported experiment within experimental resolution. But this is not the most general prediction.

The experiment can be seen as providing one further anomaly explainable in TGD based model of dark matter based on hierarchy of phases with Planck constant of Poincare algebra which is integer multiple of ordinary Planck constant. Quantum groups and non-commutativity are involved with this hierarchy of phases of matter but emerge in different manner via Jones inclusions of hyperfinite factors of type II_1.

For a brief summary see my blog or my homepage .

Matti Pitkanen