WIMPs or MACHOs: Which Dark Matter Candidate Holds More Promise?

[Quds Akbar]

I have been thinking about this quite often, and I know that usually WIMPs are taken more seriously than MACHOs, and I know it is because MACHOS don't exist in such huge amounts, but why are they considered better candidates for Dark Matter?

 

[Chalnoth]

I have been thinking about this quite often, and I know that usually WIMPs are taken more seriously than MACHOs, and I know it is because MACHOS don't exist in such huge amounts, but why are they considered better candidates for Dark Matter?

The evidence of dark matter is seen clearly in the CMB, which was emitted before any compact objects could have formed.

 

[rootone]

Aha, I had been wondering about this quite a while, why have MACHOs been discounted as a DM candidate by most people working on it.
The idea that DM could be explained by there being a large amount of small material objects which simply are not visible to us because they are too small and dark always did seem like a simplest explanation to me.
Is the evidence of DM existing in the CMB data a hard certainty, or is it the 'strongly likely' category?

 

[Chronos]

There are certain asumptions used that could affect our interpretations regarding dark matter. For example, it is assumed radiation density in the early universe was fixed. If you relax that assumption other interpretations are possible. See http://background.uchicago.edu/~whu/intermediate/driving2.html for discussion. There was a time it was speculated primordial black holes could account for dark matter, but, after extensive study and analysis of the permissible mass range for PBH's has nearly exhausted any possibility of them as a dark matter candidate.

 

[Jorrie]

See http://background.uchicago.edu/~whu/intermediate/driving2.html for discussion.

Thanks for sharing! The last page of that piece is one of the very best summaries that I've seen on the subject of the CMB.

 

[phyzguy]

Also, Big Bang Nucleosynthesis very tightly constrains the baryon content of the universe, and the required baryon content is quite consistent with what is derived from the CMB. So the dark matter can not be made of ordinary atoms. This pretty much eliminates MACHOS as a possibility.