## CosmoMC: light element abundance datasets

Use of Healpix, camb, CLASS, cosmomc, compilers, etc.
Posts: 18
Joined: July 17 2014
Affiliation: Johns Hopkins University

### CosmoMC: light element abundance datasets

Hi,

I'm interested in including measurements of deuterium / helium3 abundances in a fit. In batch2/abundances.ini it says

Code: Select all

abundance_dataset&#91;Izotov&#93;= %DATASETDIR%Yp_Izotov2014.dataset

#Do not include Cooke, current AlterBBN grid is not accurate enough &#40;rate issues etc&#41;
#abundance_dataset&#91;Cooke&#93;= %DATASETDIR%D_Cooke2013.dataset
What exactly is the issue for the Cooke2013 deuterium constraint? Is the comment saying that the conversion from input obh2 / nnu etc params to a predicted D/H is not accurate enough given the Cooke2013 error?

For helium is there any similar issue? Or can I replace Izotov with other Yp constraints without worrying about this?

Thanks a lot

Antony Lewis
Posts: 1379
Joined: September 23 2004
Affiliation: University of Sussex
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### Re: CosmoMC: light element abundance datasets

The comment may be old, the default grid is not based on AlterBBN. The Helium results are also more stable.

Posts: 18
Joined: July 17 2014
Affiliation: Johns Hopkins University

### CosmoMC: light element abundance datasets

OK I see. I had missed the data/bbn.py file initially. Looking at that file, it seems that the assumed neutron lifetime can be adjusted (just by editing tau_n in line 25) but that the reaction rate that dominates the deuterium uncertainty d(p,\gamma)^{3}He is hardcoded. Do you know if there have been any PArthENoPE updates using different / more recent numbers for the d(p,\gamma)^{3}He rate? E.g. from this paper http://adsabs.harvard.edu/abs/2016PhRvL.116j2501M , which was used in one of the recent Cooke et al. deuterium analyses https://arxiv.org/abs/1607.03900