# Axion thrust by enhanced scattering

1. Jun 25, 2015

### Ricvil

Axions in theory are uncharged, spin 0, very light particles, and have a very small scattering cross section when interacting with photons.
But there is a very interesting article about a strong enhanced scattering of neutral particles. "Resonant radiation pressure on neutral particles in a waveguide"- arxiv.org/pdf/physics/0103017
The article above talks about a ressonant backscattering of neutral particles, where under right conditions of frequency, a "arbitrarily small" polarizable scatter in a waveguide can have a huge effective scattering cross section.
Well, the axion has the electrodynamic property of produce electromagnectic polarization due to axion-photon mixing, so axion could be accelerated by resonant geometrical scattering inside waveguides under critical frequency of unimodal propagation, generating a axion thrust?

2. Jun 25, 2015

### ChrisVer

I think this paper is talking about particles in the Rayleigh regime...
I looked for this, and eg here http://patarnott.com/pdf/Moosmuller2009JAWMA.pdf it gives some explanation on what Rayleigh particles are...I don't think this can be generalized to axions? I mean in the parameter $x= \frac{2 \pi r}{\lambda} \ll 1$, what would $2 \pi r$ stand for? the axion doesn't have a circumference.
Why would you accelerate axions? if you apply an external electromagnetic field, the axion will generally produce a photon (the reverse??? Primakoff process), of course dependent on the polarization of your field (due to the coupling to F Ftilde). So I don't think you could accelerate it, rather than change it.

3. Jun 25, 2015

### Staff: Mentor

The "neutral particles" in the paper are things like dust particles. Not with an overall charge, but still made out of electrons and nuclei, which obviously show a significant interaction with photons.
Axions, if they exist at all, are so rare and couple so weakly to matter or light that there is nothing you could accelerate.

4. Jun 26, 2015

### Ricvil

The Primakoff process ( in this context) models the resulting interaction between photon and axion fields under a strong and "static/stationary" background electromagnetic field, producing a aproximate linear model of axion photon electrodynamic.
Basicaly, the Primakoff process models a very paticular situation of a "photon axion oscillation"
Rayleigh scattering is another example of a very particular situation of the most general electromagnectic scattering process.
The article about ressonante scattering is interesting because it shows a process where the transmission of electromagnectic waves (photons with momentum) inside a waveguide can be totaly reflected (inversion of all photons momentuns) by a "arbitrarily small polarizable scatter".
Changes on momentum of photons must be compensated by the change of mometum of the scatter(force on the scatter).
If the scatter is free to move then it will accelerate.
The question:
Is the axion a effective "small polarizable scatter"?

Last edited: Jun 26, 2015
5. Jun 26, 2015

### ChrisVer

What is the probability of a photon to scatter on the axion? or how could you explain this interaction: $a \gamma \rightarrow a \gamma$??

6. Jun 27, 2015

### Ricvil

The process are between two photons and one axion in quantum terminology.
I prefer look this process by axion electrodynamic field equations point of view, where the scattering process is more friendly.
For example, i have found this interesting article associating axion photon oscillation with a index of refraction point of view.
http://arxiv.org/abs/1003.0410
In this article, photon and axions fields are scattered by a strong inhomogeneous magnectic field.
The axion mass was not taked in consideration.
Perhaps the effect of ressonant backscattering in waveguide can be triggered by a strong inhomogeneous magnectic field applied on a section of the waveguide.

7. Jun 27, 2015

### Ricvil

Another interesting article from condensate matter axion electrodynamic
http://arxiv.org/pdf/1503.00235
The axion field causes a "cross-polarization"
The article presents the expressions for the scattering caused by spheres of "topological isolators"

8. Jun 28, 2015

### Ricvil

Sorry, is "Topological insulators".

9. Jun 28, 2015

### Staff: Mentor

This thread is becoming a collection of buzzwords with unclear relations and wild speculations. Not something we like to see here.
If you have some reference discussing the precise effect you are asking about, please send me a message and I'll open the thread again. Until then it remains closed.