<p>The original research <a href="http://arxiv.org/pdf/1303.5076v1.pdf" rel="nofollow">paper</a>, p.43, section 6.3.2.</p>

<p>I leave it to someone else to find comprehensible words to describe the connection between CMB, redshift and effective neutrino number.</p>

CC BY-SA 3.0
2016-10-20T19:10:52.560Z
While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference.  Link-only answers can become invalid if the linked page changes. - [From Review](/review/low-quality-posts/8805)
SE - stop firing the good guys
CC BY-SA 3.0
2016-10-26T18:06:32.913Z
@Hohmannfan Converted to wiki at Gerald's request so that others can make the necessary modifications to beef up the answer. Gerald is currently busy.
called2voyage
CC BY-SA 4.0
2021-11-04T00:05:12.610Z
The link does not work anymore.... What was the exact name of the original research paper it is supposed to link to?
Kurt Hikes
CC BY-SA 3.0
2014-01-06T05:14:12.253Z
2014-01-06T15:24:43.827Z
2014-01-06T15:24:43.827Z
Gerald
<p>I've asked this <a href="https://physics.stackexchange.com/questions/81911/how-does-cosmology-constrain-the-number-of-neutrino-species">question</a> already on the Physics SE, but I felt it would be worth posting here as well.</p>

<p>I know that based upon theories of structure formation cosmologists can constrain the <strong>sum</strong> of the masses of neutrinos - if neutrinos were too light or too heavy it would simply change the power spectrum of the universe. </p>

<p>My question is how exactly is the number of neutrino species constrained by cosmological measurements (i.e. - $N_{eff}$ as measured by WMAP or Planck)? The recent results from the Planck Satellite give us $3.3\pm0.3$, which is consistent with three neutrino species. How is this measured?</p>

<cosmology><neutrinos>
How Does Cosmology Constrain the Number of Neutrino Species?
astromax
# How Does Cosmology Constrain the Number of Neutrino Species?

(Asked by: username_0 on 2013-10-23)

I've asked this [question](https://physics.stackexchange.com/questions/81911/how-does-cosmology-constrain-the-number-of-neutrino-species) already on the Physics SE, but I felt it would be worth posting here as well.

I know that based upon theories of structure formation cosmologists can constrain the **sum** of the masses of neutrinos - if neutrinos were too light or too heavy it would simply change the power spectrum of the universe.

My question is how exactly is the number of neutrino species constrained by cosmological measurements (i.e. - $N\_{eff}$ as measured by WMAP or Planck)? The recent results from the Planck Satellite give us $3.3\pm0.3$, which is consistent with three neutrino species. How is this measured?

**Tags:** cosmology, neutrinos

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## 1 answers

### Answer by username_1 on 2014-01-06. Score: 5

The original research [paper](http://arxiv.org/pdf/1303.5076v1.pdf), p.43, section 6.3.2.

I leave it to someone else to find comprehensible words to describe the connection between CMB, redshift and effective neutrino number.

> **Comments:**
> **username_2**: While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference.  Link-only answers can become invalid if the linked page changes. - [From Review](/review/low-quality-posts/8805)  
> **username_3**: @Hohmannfan Converted to wiki at Gerald's request so that others can make the necessary modifications to beef up the answer. Gerald is currently busy.  
> **username_4**: The link does not work anymore.... What was the exact name of the original research paper it is supposed to link to?  

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