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CosmoMC: light element abundance datasets
 
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Graeme Addison



Joined: 17 Jul 2014
Posts: 11
Affiliation: Johns Hopkins University
PostPosted: February 15 2017  Reply with quote
Hi,

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

Code:
abundance_dataset[Izotov]= %DATASETDIR%Yp_Izotov2014.dataset

#Do not include Cooke, current AlterBBN grid is not accurate enough (rate issues etc)
#abundance_dataset[Cooke]= %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
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Antony Lewis



Joined: 23 Sep 2004
Posts: 1243
Affiliation: University of Sussex
PostPosted: February 15 2017  Reply with quote
The comment may be old, the default grid is not based on AlterBBN. The Helium results are also more stable.
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Graeme Addison



Joined: 17 Jul 2014
Posts: 11
Affiliation: Johns Hopkins University
PostPosted: February 15 2017  Reply with quote
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,γ)3He is hardcoded. Do you know if there have been any PArthENoPE updates using different / more recent numbers for the d(p,γ)3He 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

Thanks again for your help.
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Antony Lewis



Joined: 23 Sep 2004
Posts: 1243
Affiliation: University of Sussex
PostPosted: February 15 2017  Reply with quote
I don't know of any updates - you could ask them. (would be great if they could produce a numerical interpolation table, rather than a fitting formula which is presumably less accurate).
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