All Questions
73
questions
54
votes
4
answers
14k
views
How do we know Dark Matter isn't simply Neutrinos?
What evidence is there that dark matter isn't one of the known types of neutrinos?
If it were, how would this be measurable?
- 705
30
votes
3
answers
2k
views
What does the cosmic neutrino background look like today, given that neutrinos possess mass?
This question is inspired by (or a follow-up to) the threads Where are all the slow neutrinos? and Is it possible that all “spontaneous nuclear decay” is actually “slow neutrino” induced?
The cosmic ...
22
votes
2
answers
3k
views
Why are neutrinos ruled out as a major (or even sole) component of dark matter?
A number of times I have encountered in text-books and articles that neutrinos might contribute only a small fraction to dark matter. The reason has to do with the fact that if all of the dark matter ...
- 547
20
votes
3
answers
8k
views
Why do neutrino oscillations imply nonzero neutrino masses?
Neutrinos can pass from one family to another (that is, change in flavor) in a process known as neutrino oscillation. The oscillation between the different families occurs randomly, and the likelihood ...
- 1,516
16
votes
1
answer
507
views
Do primordial background neutrinos orbit in dark matter halos?
According to Wikipedia, neutrinos separated from other matter seconds after the Big Bang and formed a separate background radiation field which now fills space at a temperature ~2 K.
Supposing ...
- 1,300
14
votes
3
answers
917
views
How would cold neutrinos get trapped by stars?
Continuing on from the cool physics Q&A'd on the threads Where are all the slow neutrinos?, Is it possible that all "spontaneous nuclear decay" is actually "slow neutrino" ...
- 134k
13
votes
0
answers
382
views
Are there any experimental bounds on the ratio of neutrinos to antineutrinos in the universe?
In the Standard Model, both baryon number and lepton number are conserved quantities (excluding the theoretical possibility of sphaleron processes which are exceeding rare, at least at non-"near in ...
- 3,957
12
votes
2
answers
900
views
If we could build a telescope to view the cosmic neutrino background, what would we see?
If we could build a neutrino telescope capable of viewing relic neutrinos that decoupled after the big bang, with a similar angular and spectral resolution that is possible now for the CMB (e.g. with ...
- 133k
11
votes
2
answers
547
views
If neutrinos are disfavoured as DM candidates why aren't axions?
Numerical simulations of observed large-scale structure formation work best with Cold Dark Matter (CDM; see the answer here). Neutrinos are candidates for Hot Dark Matter (HDM), and hence they cannot ...
- 26.8k
11
votes
2
answers
448
views
Cold neutrinos - how are they distributed?
Cold or slow neutrinos have non-relativistic velocities and hence very low energies. That makes them very difficult to detect. Answers to Where are all the slow neutrinos? make it clear that they are ...
- 7,438
10
votes
1
answer
442
views
Are neutrinos and sterile neutrinos both dark matter candidates?
Are both neutrinos and sterile neutrinos candidates for dark matter?
In particular, why would "standard" neutrinos be a candidate for dark matter, since they interact with matter?
Why would ...
8
votes
2
answers
256
views
Reference frame for the Cosmic Neutrino Background
It is well known that there exists a reference frame where the total momentum of the Cosmic Microwave Background is zero (a basic fact of special relativity applied to a collection of massless ...
- 5,684
8
votes
2
answers
128
views
What is the composition of the universe's population of neutrinos?
I believe earth-based detectors measure mainly solar neutrinos, which have energies on the MeV scale of nuclear physics, are directed from the sun, and have flavors determined by the sun's nuclear ...
user4552
7
votes
1
answer
826
views
Neutrino energy density vs photon energy density
So I'm currently following a course in Cosmology and we're covering the densities of different species in the universe right now. Starting from the photon density $\rho_{\gamma}$ we need to derive the ...
- 548
7
votes
2
answers
146
views
Puzzled by a new result on neutrino speeds
In a paper appearing today on arXiv, Wie et al. have used the close coincidence of the time of arrival of gamma rays from GRBs and the detection of single 3-30 TeV neutrinos at the IceCube observatory,...
- 133k