What is the Freeze-Out Temperature of WIMP Particles?

[happyparticle]

TL;DR

Is the epoch of freeze-out temperature for wimps particles is the same as for neutrinos.
Why the wimps freeze-out happened earlier.

I'm studying the freeze-out moment of different particles and I have few questions that I can't find answer about the Wimp particles.

First of all, the freeze-out temperature of the wimp particles is around 0.4-40gev much higher than 1 mev for the neutrinos.
Thus, that means that the freeze-out moment for the wimp particles happened earlier, but why exactly? It it related with the mass of the wimp particles?

Also, does it means that the freeze-out moment happened during the radiation dominated epoch?

secondly, are the wimp particles moving at the speed of light, because I see that in the relation "rate of scattering-Hubble parameter" they use v=c=1.

For example, https://itp.uni-frankfurt.de/~philipsen/homepage_files/graz.pdf the author seems to use c=1. I might be wrong though.
Also, using the relation in the link above (p.10) $n G_f^2 m_q^2 = \frac{T^2}{m_p}$, I don't see how the author get a relation for the temperature-mass using his expression, same for the neutrinos.

 

[Vanadium 50]

Freeze out happens when T ≈ m.

 

[Orodruin]

Freeze out happens when T ≈ m.

Someone should tell the CNB neutrinos ...

 

[Orodruin]

First of all, the freeze-out temperature of the wimp particles is around 0.4-40gev much higher than 1 mev for the neutrinos.

First of all, you should write your units appropriately. There is a difference between GeV and gev and there is a difference between MeV and mev, which may be misunderstood as meV (which is 9 orders of magnitude smaller than MeV).

Thus, that means that the freeze-out moment for the wimp particles happened earlier, but why exactly? It it related with the mass of the wimp particles?

Yes. I may have smirked a bit about the mass comment above, but there is a difference in the freeze out of relativistic species and non-relativistic species. If temperature drops to the point of a species becoming non-relativistic, then its equilibrium abundance becomes Boltzmann suppressed. This leads to the abundance quickly dropping off, leading to fewer interactions than what you would expect from a relativistic species and therefore facilitating the freeze out.

Meanwhile, a relativistic species (such as neutrinos at freeze out) does not have its abundance Boltzmann suppressed and will not freeze out due to the abundance dropping. This should be covered in any basic textbook such as Kolb & Turner.

 

[happyparticle]

All right. Thank you. It took me some time to really understand. Your answer helped me. Thanks again.