2

I don't understand the answer to this question: axion couplings

There are experiments trying to measure how light is shining through a wall, using the coupling of the strong cp fixing axion to the SM photon.

But is this coupling of the axion directly to the photon (as I saw in many related Feynman diagrams) or via a fermion loop as suggested by the answer in the above stated link?

So in other words is there a $a F^{\mu\nu} F_{\mu\nu}$ term in the suggested Lagrangian where $F$ is the EM field strength and $a$ the axion field?

Gabriel Ybarra Marcaida
  • 2,415
  • 1
  • 5
  • 32
Mr Puh
  • 655

1 Answers1

2

The coupling to the photon is through a quark loop. Axions are part of QCD (and, so, interacting with quarks). By the way the triangle diagram connects one axion and two photons.

The linked answer is comprehensive so I'm not really adding anything, but it's also undoubtedly technical.

Helen
  • 904