How confident are we of the neutrino CMB energy density?

In summary, an entropy argument has led to the conclusion that the CMB neutrino temperature is (4/11)1/3 of the CMB photon temperature, assuming massless neutrinos. While neutrinos have a small but non-zero mass, it is not clear how this affects the previous conclusion. The contribution of neutrinos to the present energy density is small, but was significant in the past, particularly at the time of the Last Scattering Surface. It is uncertain how reliable this conclusion is, and if there are any other analyses that could potentially yield different results. The 7Li problem, which deals with primordial nucleosynthesis, is still being studied and it is unclear if there is a way to reconcile it. Overall,
  • #1
BillSaltLake
Gold Member
184
0
From an entropy argument it is concluded that the CMB neutrino temperature is (4/11)1/3 of the CMB photon temperature. This assumes massless neutrinos. Although neutrino contribution to the present energy density is therefore very small, it was significant must earlier, such as at the time of the Last Scattering Surface. How reliable is this conclusion? Is there a different analysis that would yield a different result, so that for example 7Li nucleosynthesis might be reconciled (although I'm not sure that there is an adjustment of the neutrino density that could fix the Li problem)?
 
Last edited:
Space news on Phys.org
  • #2
From what I have read, neutrinos have a small but non-zero mass.
I'm not sure how that effects everything though.
 
  • #3
I hadn't heard of the 7Li problem until now. Here is a paper that may help others who, unlike me, aren't familiar with it: http://arxiv.org/abs/0808.2818
 
  • #4
BillSaltLake said:
From an entropy argument it is concluded that the CMB neutrino temperature is (4/11)1/3 of the CMB photon temperature. This assumes massless neutrinos. Although neutrino contribution to the present energy density is therefore very small, it was significant must earlier, such as at the time of the Last Scattering Surface. How reliable is this conclusion? Is there a different analysis that would yield a different result, so that for example 7Li nucleosynthesis might be reconciled (although I'm not sure that there is an adjustment of the neutrino density that could fix the Li problem)?
Well, neutrinos have long been taken into account in CMB observations, so I really doubt it.

But in any event, the 7Li problem is way, way down at the tail of primordial nucleosynthesis where it is very hard to measure. At present we just can't say for sure whether the problem appears as a result of our lack of understanding of stellar physics, or whether it's our lack of understanding of some of the precise details of big bang nucleosynthesis.
 
  • #5
Here's a paper that just came out today arxiv.org/abs/1107.1117 that talks about the 7Li problem.
 

Related to How confident are we of the neutrino CMB energy density?

1. What is the current estimate of the neutrino CMB energy density?

The current estimate of the neutrino CMB energy density is approximately 0.001 eV/cm^3. This value is derived from observations of the cosmic microwave background (CMB) radiation and the Standard Model of particle physics.

2. How is the neutrino CMB energy density measured?

The neutrino CMB energy density is measured indirectly through observations of the CMB. The CMB is a remnant of the early universe, and it contains information about the energy density of all particles present at that time, including neutrinos. Scientists use sophisticated mathematical models and data from experiments like the Planck satellite to estimate the neutrino CMB energy density.

3. How confident are we in the current estimate of the neutrino CMB energy density?

Scientists are fairly confident in the current estimate of the neutrino CMB energy density. The value is consistent with predictions from the Standard Model and data from various experiments. However, there is still some uncertainty due to the complexities of measuring and modeling the CMB.

4. Could the neutrino CMB energy density be different in other parts of the universe?

Yes, it is possible that the neutrino CMB energy density could vary in different regions of the universe. This could be due to various factors, such as the presence of dark matter or interactions with other particles. However, the current estimate is based on the average energy density of the entire observable universe.

5. How does the neutrino CMB energy density affect the evolution of the universe?

The neutrino CMB energy density is an important factor in the evolution of the universe. It influences the expansion rate of the universe and the formation of large-scale structures, such as galaxies and galaxy clusters. Understanding the neutrino CMB energy density helps scientists better understand the history and future of the universe.

Similar threads

B Can we observe anything beyond the CMB 'wall'?
    • Cosmology
Replies
5
Views
2K
I Some questions about Cosmic Microwave Background radiation
    • Cosmology
Replies
13
Views
2K
Are thermalized neutrinos stable at temperatures their rest energy?
    • Cosmology
Replies
4
Views
4K
I Modified Newtonian Dynamics + dark matter sterile neutrinos or PBH?
    • Beyond the Standard Models
Replies
7
Views
2K
I How do the collider experiments measure the mass of the W boson?
    • High Energy, Nuclear, Particle Physics
Replies
4
Views
2K
Can the Li7 problem be resolved by increasing the dark matter ratio?
    • Cosmology
Replies
4
Views
2K
Estimating Neutrino Flux Density
    • Advanced Physics Homework Help
Replies
5
Views
2K
Is the universe eternal and cyclic? Evidence from the CMB
    • Cosmology
Replies
8
Views
6K
I How powerful would a collider have to be to observe a sphaleron?
    • High Energy, Nuclear, Particle Physics
Replies
2
Views
2K
I Exploring ΛCDM Model: Cosmology Intertwined in 4 Pre-Prints
    • Cosmology
Replies
1
Views
1K

Hot Threads

Recent Insights

Back
Top