Do Dark Matter Axion Bose-Einstein Condensates Thermalize?

by Tommy on 21/01/2017

So looking around superficially I ran across this. I never really dug deeply into the BEC aspects of axions since I’m fairly familiar with the subject, but now I can see it’s a little more complicated than I thought. I never was a big fan of axion stars, though. Personally, I think that the deeper quantum field theory connections with the baryons prohibits that. That’s all to be developed.

Do Dark Matter Axions Form a Condensate with Long-Range Correlation?, Alan H. Guth, Mark P. Hertzberg and C. Prescod-Weinstein, Phys. Rev. D 92, 103513 (16 November 2015), DOI:10.1103/PhysRevD.92.103513, MIT-CTP 4625

Recently there has been significant interest in the claim that dark matter axions gravitationally thermalize and form a Bose-Einstein condensate with cosmologically long-range correlation. This has potential consequences for galactic scale observations. Here we critically examine this claim. We point out that there is an essential difference between the thermalization and formation of a condensate due to repulsive interactions, which can indeed drive long-range order, and that due to attractive interactions, which can lead to localized Bose clumps (stars or solitons) that only exhibit short range correlation. While the difference between repulsion and attraction is not present in the standard collisional Boltzmann equation, we argue that it is essential to the field theory dynamics, and we explain why the latter analysis is appropriate for a condensate. Since the axion is primarily governed by attractive interactions — gravitation and scalar-scalar contact interactions — we conclude that while a Bose-Einstein condensate is formed, the claim of long-range correlation is unjustified.

Of course with gravitational axions, all bets would be off concerning the excitation spectrum.

Regardless, this is an excellent introduction to the subject.

Ironically, this is when my adventure started.

I want this adventure to be over now.

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