Explain Dark Matter: Verlinde's Theory Tested

[Carlos L. Janer]

Not necessarily. The prototypical HDM is neutrinos. Neutrinos don't radiate.

Hot means "relativistic". If they move that fast, they exceed escape velocity for galaxies and clusters.

I do not know if my question is stupid but, what is the general consensus about relic neutrinos? Are they also relativistic particles or could their velocities have dropped well below the speed of light?

 

[phinds]

I do not know if my question is stupid but, what is the general consensus about relic neutrinos? Are they also relativistic particles or could their velocities have dropped well below the speed of light?

Given the almost total lack of interaction between neutrinos and anything else, what would you expect to slow them down?

 

[Carlos L. Janer]

Given the almost total lack of interaction between neutrinos and anything else, what would you expect to slow them down?

The expansion of the universe?

 

[phinds]

The expansion of the universe?

Not sure about that but you may be right. Light always arrives traveling at c (but is red shifted due to expansion) but of course light is special.

 

[Carlos L. Janer]

Not sure about that but you may be right. Light always arrives traveling at c (but is red shifted due to expansion) but of course light is special

I cannot be right because I do not know anything. I just pointed out that there might be a way for relic neutrinos to slow down just because they are not massless. But I completely ignore what cosmologists think about this subject.

 

[phinds]

I cannot be right because I do not know anything. I just pointed out that there might be a way for relic neutrinos to slow down just because they are not massless. But I completely ignore what cosmologists think about this subject.

Well, I don't know anything either but I never let that stop me from thinking I'm right

 

[Carlos L. Janer]

Well, I don't know anything either but I never let that stop me from thinking I'm right

That's a good one!

 

[PAllen]

Relic neutrinos are at a low temperature, with standard analyses showing this temperature to be lower than CMB. However there is uncertainty due to lack knowledge of neutrino mass. The consensus is certainly that they cannot explain much of the observations that fall under the umbrella of "dark matter".

 

[Carlos L. Janer]

Relic neutrinos are at a low temperature, with standard analyses showing this temperature to be lower than CMB. However there is uncertainty due to lack knowledge of neutrino mass. The consensus is certainly that they cannot explain much of the observations that fall under the umbrella of "dark matter".

OK, but that statement still leaves the subject that Phinds and I were discussing unanswered. Relic photons may not be relevant in terms of cosmological expansion at present times but what we were talking about was if expansion could slow them down to non-relativistic velocities. We simply do not know and we would like to. Or, at least, we would like to know if such an scenario is conceivable or it is just plain crazy.

 

[PAllen]

OK, but that statement still leaves the subject that Phinds and I were discussing unanswered. Relic photons may not be relevant in terms of cosmological expansion at present times but what we were talking about was if expansion could slow them down to non-relativistic velocities. We simply do not know and we would like to. Or, at least, we would like to know if such an scenario is conceivable or it is just plain crazy.

It's not my expertise, especially given that old analyses assuming massless neutrinos are not accurate anymore. It is correct that relic neutrinos have enormously lower energy than would have been measured at emission, for the same reasons as CMB, which you can poetically call expansion of space (I prefer a different mental model, but it is the same equations). I just do not know, when combined with uncertainties about neutrino mass, whether this leaves the possibility of some significant number having non-relativistic velocities. Hopefully, someone else here, who is up to date on the issues can answer.

 

[Carlos L. Janer]

It's not my expertise, especially given that old analyses assuming massless neutrinos are not accurate anymore. It is correct that relic neutrinos have enormously lower energy than would have been measured at emission, for the same reasons as CMB, which you can poetically call expansion of space (I prefer a different mental model, but it is the same equations). I just do not know, when combined with uncertainties about neutrino mass, whether this leaves the possibility of some significant number having non-relativistic velocities. Hopefully, someone else here, who is up to date on the issues can answer.

Thank you very much!

 

[stoomart]

I do not know if my question is stupid but, what is the general consensus about relic neutrinos? Are they also relativistic particles or could their velocities have dropped well below the speed of light?

Seems off-topic from this thread, but neutrinos do not travel at the speed of light because they have mass. Also check out 'neutrino decoupling' and 'cosmic neutrino background'.

 

[PAllen]

Seems off-topic from this thread, but neutrinos do not travel at the speed of light because they have mass. Also check out 'neutrino decoupling' and 'cosmic neutrino background'.

The question was about neutrinos moving slow compared to light relative to comoving bodies. To even ask this question means there is no implication of any neutrino moving at c.

Further, most hits on your proposed search do not address this question, others are paywalled. However, I did finally turn up the following, which suggests at least some of flavors of relic neutrinos are non-relativistic.
https://arxiv.org/abs/1212.6154

 

[Carlos L. Janer]

The question was about neutrinos moving slow compared to light relative to comoving bodies. To even ask this question means there is no implication of any neutrino moving at c.

Further, most hits on your proposed search do not address this question, others are paywalled. However, I did finally turn up the following, which suggests at least some of flavors of relic neutrinos are non-relativistic.
https://arxiv.org/abs/1212.6154

Thanks again for your help.

 

[Mordred]

Interesting article PAllen enjoyed reading it

 

[Adrian59]

Thanks Bandersnatch. I had not heard of the bullet cluster or the power spectrum of BAO's before. I will do some research about these.

However, I feel a note of caution is needed, as despite what the dark matter fraternity say; the idea that the Bullet cluster is evidence for dark matter is not unchallenged. A couple of early papers from 2010 and 2011 suggested that the in-fall velocity was too high to support dark matter. A more recent paper by Craig Lage and Glennys R. Farrar published 25 February 2015 in Journal of Cosmology and Astroparticle Physics, concluded “due to the paucity of examples of clusters with such a high mass in simulations, these features of the main cluster cannot presently be used to test ΛCDM.”

 

[RUTA]

However, I feel a note of caution is needed, as despite what the dark matter fraternity say; the idea that the Bullet cluster is evidence for dark matter is not unchalleged.”

Moffat's modified gravity (MOG) addresses the Bullet Cluster without DM for example https://arxiv.org/abs/astro-ph/0702146