## How to put a hard prior on w_de with CPL equation of state parametrization?

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

### How to put a hard prior on w_de with CPL equation of state p

Dear Anthony et al,

say I am using the CPL parametrization for the dark energy equation of state (or for that matter, any other 2-parameter parametrization of the equation of state), which is implemented in line 98 of camb/equations_ppf.f90:

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w_de=w_lam+wa_ppf*&#40;1._dl-a&#41;
If I understand this correctly, I can then put hard priors on w_lam and wa_ppf through param[w]= and param[wa]= in my ini file. Is this correct so far?

However, say I want to put a hard prior on w_de instead (which is given by the combination of w and wa if I understood this correctly), say e.g. I want w_de>-1 because I am studying a quintessence model, how do I impose this?

Thanks a lot! Cheers,
Sunny

Antony Lewis
Posts: 1369
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

### Re: How to put a hard prior on w_de with CPL equation of sta

You'd have to write your own prior, e.g. in TP_NonBaseParameterPriors in CosmologyParameterizations.f90.

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

### How to put a hard prior on w_de with CPL equation of state p

Dear Anthony,

thanks for your help! I looked into TP_NonBaseParameterPriors. Would it be sufficient to have something like:

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if &#40;CMB%w_de < -1.0&#41; return
assuming I want to set w_de>-1? Would this ensure that w_de would be -1 for any value of redshift z>0?

Cheers,
Sunny