## Massive neutrinos in pyCAMB

Use of Healpix, camb, CLASS, cosmomc, compilers, etc.
Chris Pedersen
Posts: 5
Joined: March 01 2018
Affiliation: University College London

### Massive neutrinos in pyCAMB

Just have a couple of questions about massive neutrinos in pyCAMB:

1. What is the difference between nnu and standard_neutrino_neff?

2. Trying to generate a simple LCDM + massive neutrino cosmology with 3 active neutrinos, no sterile, in a normal mass hierarchy in the following way:

Code: Select allp>

pars.set_cosmology&#40;H0=67.24, ombh2=0.0223, omch2=0.11450538973588147, omk=0.0, num_massive_neutrinos=3,
mnu=0.4, nnu=3.046, YHe=0.24, meffsterile=0.0, standard_neutrino_neff=3.046,
TCMB=2.718, tau=None, deltazrei=None, bbn_predictor=None&#41;
However when we print out the parameters, we get:

num_nu_massless = 4.440892098500626e−16

Should we not expect num_nu_massless to be 0.046, since we have 3 massive neutrinos but our Neff is set to 0.046?

Thanks!

Antony Lewis
Posts: 1352
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

### Re: Massive neutrinos in pyCAMB

I don't think so, the 0.046 is because the neutrinos are a bit heated at electron positron annihilation, which should increase the number of standard massive neutrinos not add additional fractional massless ones.