# Can photon couple to scalar field?

1. Jun 3, 2008

### arroy_0205

I have seen in one paper that photon is coupled to dilaton field which is scalar and motivated by string theory. I do not understand this. Photon is carrier of electromagnetic field and so I thought it can only couple to electrically charged fields. Can anyone explain?

2. Jun 4, 2008

### Timo

Photons can couple to scalar fields. There just happens to be none in the Standard Model (in the spontaneously broken state). Don't want to search for my Rosiek paper now but I am pretty sure the photon couples to the Selectrons of SUSY, for example. In standard particle physics photons only couple to charged fields but in exotic physics they might couple to gravity which the dilaton (according to the WP article; I never encountered those guys myself) seems to be related to.

3. Jun 6, 2008

### jdstokes

Scalar fields carry charge as long as they are complex.

4. Jun 6, 2008

### arroy_0205

Yes that is true but the one I talked about was real scalar field. That is the source of confusion. This I did not write explicitly in my question.

5. Jun 6, 2008

### mormonator_rm

Well, I am not up-to-snuff on string theory per se, but I would say that any scalar object with internal charges, whether they cancel or not, will couple to a photon through a trilinear coupling involving another appropriate vector particle. For neutral scalar mesons, for example, the coupling to two photons is an available channel...

6. Jun 9, 2008

### blechman

photons can couple to fields that are electrically neutral through higher-dimension operators (and therefore are suppressed). All you need to do is maintain gauge and Lorentz invariance, so for example (with a real scalar field $\phi$):

$$\phi F_{\mu\nu}F^{\mu\nu}$$

is allowed. However, it's physical effects are typically quite small. But this is how you can describe photons scattering off (neutral) atoms in the atmosphere, for example.

7. Jun 10, 2008

8. Jul 9, 2008

### ghery

Hi:

In QFT, photons are the carriers of the electromagnetic force, right?, Does that mean that if photons pass between charges , they don't feel any force at all?

I am a little bit confused about how the interactions occur in QFT, I'd be glad if you could please explain me

Thanks