Big Bang Nucleosynthesis (BBN)

[SafaeCosmology]

Hello everyone, I have a question regarding BBN data, I want to know please the difference between bbn and _bbn_omegab_ Likelihood. Thank you in advance.

[brinckmann]

Hi Safae,

@schoeneberg is the best person to answer this question. I give the answer I got from him previously, but tag him in case he has anything to add.

This is a bit of a philosophy question. For most cases, eta_b is the more direct quantity relevant for BBN, but personally I am of the philosophy to let codes deal with the conversion instead of trying to do it ourselves, and thus simply using the bbn_omega_b likelihood.

Best, Thejs

[schoeneberg]

Dear @SafaeCosmology ,

the "bbn" likelihood is based on the BBN parameter "eta_b = number abundance of baryons/number abundance of photons" instead of being based on the more well known "omega_b" like the "bbn_omegab" likelihood. Usually you will want to use the "bbn_omegab" likelihood, I would say.

I suggest we might unify at some point the likelihoods and make the underlying used parameter a new option, since this has indeed created a bit of confusion for many people.

Let me know if there's anything else, Nils Sch.

[SafaeCosmology]

Thank you very much for your answer