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Is the x_e equation in CAMB correct or not?
 
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YinZhe Ma



Joined: 09 Oct 2008
Posts: 11
Affiliation: University of KwaZulu-Natal

PostPosted: July 31 2017  Reply with quote

I am looking at the Antony Lewis' paper

https://arxiv.org/pdf/0804.3865.pdf

for Eq.(B3) on page 11, there is this equation of number of free electron per hydrogen atom.

But for this equation, if z large values, then y=(1+z)3/2 will also become large values, while y(zre) and Δy are fixed. Since "tanh(x→∞)→1", then for large redshift, xe→1.

If z→0, then tanh function will becomes a negative value but greater than −1, then xe→0.

So this is completely opposite to the trend of Fig.6 on the same page. Can anyone explain what is going on here?

Perhaps I made some stupid mistake, please point it out. Thank you.
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Antony Lewis



Joined: 23 Sep 2004
Posts: 1303
Affiliation: University of Sussex

PostPosted: July 31 2017  Reply with quote

I think it's just a typo (code has y(zre)-y in the tanh):

https://github.com/cmbant/CAMB/blob/master/reionization.f90#L80
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YinZhe Ma



Joined: 09 Oct 2008
Posts: 11
Affiliation: University of KwaZulu-Natal

PostPosted: July 31 2017  Reply with quote

Oh, then this typo affects the Planck reionization paper, the published version of Planck intermediate results XLVII. Planck constraints on reionization history,

page 5, equation 2

also takes this typo.
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