## [CAMB] $N_{eff}$ and taking derivatives

Use of Healpix, camb, CLASS, cosmomc, compilers, etc.
Posts: 19
Joined: November 10 2016
Affiliation: FSU

### [CAMB] $N_{eff}$ and taking derivatives

Hello Dr. Lewis,

I'm interested in taking derivatives of matter power spectra with respect to $N_{eff}$ in order to get Fisher estimates.
Unfortunately, I'm confused because there seem to be two parameters with very similar names, nnu and standard_neutrino_neff.

The documentation has this to say about them:
• nnu – N_eff, effective relativistic degrees of freedom
• standard_neutrino_neff – default value for N_eff in standard cosmology (non-integer to allow for partial heating of neutrinos at electron-positron annihilation and QED effects)
I apologize, but I'm just uncertain on what is the difference between these two parameters.

Furthermore, if I wanted to slightly change $N_{eff}$, I'm unclear as to whether they should both change or only one of them.

I appreciate any assistance.

Antony Lewis
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Joined: September 23 2004
Affiliation: University of Sussex
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### Re: [CAMB] $N_{eff}$ and taking derivatives

Use nnu. standard_neutrino_neff is fixed to the standard model calculated values for the three standard neutrinos.

Posts: 19
Joined: November 10 2016
Affiliation: FSU

### Re: [CAMB] $N_{eff}$ and taking derivatives

Thank you, Doctor Lewis.