## Putting a hard prior on w0+wa

Use of Healpix, camb, CLASS, cosmomc, compilers, etc.
Sunny Vagnozzi
Posts: 43
Joined: August 15 2016
Affiliation: Oskar Klein Centre, Stockholm University

### Putting a hard prior on w0+wa

Dear Anthony et al.,

I am running chains with the CPL parametrization w(z)=w0+wa*(1-a).

However, I am thinking of this parametrization in the context of quintessence (scalar field) dark energy models which mean w(z)>-1 for all z, which translates to w0+wa>-1. I want to impose this condition as a hard prior.

In CosmologyParametrizations.f90, within the function TP_NonBaseParameterPriors, I wrote the following:

Code: Select all

if &#40;CMB%wa + CMB%w < -1.0&#41; return
which is supposed to return logZero=10^30 (i.e. a very high chi^2) if w0+wa<-1

However, I noticed that my chains are still accepting points with w0+wa<-1 (not much smaller than -1, like -1.02 or so, but nonetheless the hard prior should cut these points out). Do you have any idea if and where my mistake is? The above is the only change I made in the source folder.

Thanks a lot! Cheers,
Sunny

Cosmo Xu
Posts: 4
Joined: March 19 2013
Affiliation: NJU/NAOC

### Putting a hard prior on w0+wa

Hi,

Have you checked the chi2 value for those points with w0+wa<-1?

Sunny Vagnozzi
Posts: 43
Joined: August 15 2016
Affiliation: Oskar Klein Centre, Stockholm University

### Putting a hard prior on w0+wa

Actually it seems to work now, so the problem should be solved!