Talk:Cosmic neutrino background

clarification
I've edited the text slightly to clarify what I think is going on. I'm not an expert in this area, so please revert if I've changed the meaning.--Eujin16 (talk) 06:15, 28 November 2007 (UTC)

Update request
Could someone knowledgeable enough include the information from ? I'm not an expert so I'd rather not do this myself. --Eleassar my talk 13:35, 8 March 2008 (UTC)
 * Done. I'll remove the update tag, and I guess noone will object if I remove the stub tag too. SwordSmurf (talk) 23:48, 28 August 2008 (UTC)

To Do

 * There are some citation needed tags
 * The derivations aren't sufficiently cited, they are just stated
 * It's too technical


 * I think the organization could be improved by adding more overview before the derivations
 * We need a link for this concept of neutrinos (and photons) decoupling I linked to the neutrino decoupling article, but we don't seem to have an article photon decoupling.
 * "Once the temperature reached approximately 2.5 MeV, the neutrinos decoupled from the rest of matter." why this temperature?


 * Can we guest the amount min/max of those neutrinos?

CMB anisotropies and structure formation
The WMAP 9 year results were released some time ago but had an error. That has now been corrected and the revised result is Neff=3.84+/-0.40 Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Parameter Results This is a significant change (essentially suggesting another species, perhaps the dark matter particle) so the article needs to be updated from the obsolete 5-year data with some words about the implications and consistency. There is a blog item about this here. George Dishman (talk) 19:07, 22 February 2013 (UTC)

Missing reference
The following quote has no reference: "Like the cosmic microwave background radiation (CMB), the CνB is a relic of the big bang; while the CMB dates from when the universe was 379,000 years old, the CνB decoupled from matter when the universe was two seconds old. It is estimated that today, the CνB has a temperature of roughly 1.95 K."

I would very much like to understand the assumptions made and the method used to calculate the numbers used in the quote, especially the "two seconds old" and "1.95 K" numbers. The article explains the derivation of the 1.95 number, but not the assumptions. My guess is that the assumptions include an assumption that the temperature varies inversely with the a(t) (the scale factor for the expansion) as is so for photons. However, that assuption assumes a state of equibrium, which is generally acknowledged to be false after the period of nuclear synthesis. If a neutrino has any rest mass, then the temperature would vary inversely with the square of a(t). (See http://arxiv.org/abs/0808.1552 Note on the thermal history of decoupled massive particles, Hongbao Zhang. Also see the discussion on the physics forum: https://www.physicsforums.com/threads/how-does-a-particles-kinetic-energy-vary-with-a-t.811627/ )

I would hope that the author of the article would be able to provide a reference that would include this information about assumptions and methods. BuzzBloom (talk) 14:23, 3 May 2015 (UTC)