CAMB - consistency relation

Use of Cobaya. camb, CLASS, cosmomc, compilers, etc.
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Minu Joy
Posts: 3
Joined: October 01 2006
Affiliation: IUCAA

CAMB - consistency relation

Post by Minu Joy » December 06 2006

If i would like to modify the code including the consistency relation, is
that ok i change the line 76 of power_tilt.f90 as

AP%rat = -6.2*ant (as per eq. (7.151) in Liddle & Lyth text book)

and change the line 73 of params.ini also accordingly.

Would you please let me know whether i should make any other changes in
the code?

Thanking you in anticipation!

Antony Lewis
Posts: 1941
Joined: September 23 2004
Affiliation: University of Sussex
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Re: CAMB - consistency relation

Post by Antony Lewis » December 06 2006

You can just edit power_tilt.f90, yes. Of course you can also just give CAMB the correct amplitude and tilt in the .ini file.

However I thought the relation here was

r = -8 n_t

(CAMB defines things in terms of the scalar curvature perturbation in early radiation domination)

Andrew Liddle
Posts: 21
Joined: September 28 2004
Affiliation: University of Lisbon

CAMB - consistency relation

Post by Andrew Liddle » December 07 2006

Hi there,

Antony is right that the coefficient should be 8. In the 1990s several different definitions of [tex]r[/tex] were in circulation, and the one our book used had [tex]r=12.4 \epsilon[/tex] where [tex]\epsilon[/tex] is the slow-roll parameter. Nowadays practically everyone, including CAMB, WMAP, etc, defines [tex]r=16\epsilon[/tex], which gives [tex]r=-8n_{{\rm T}}[/tex].

best,

Andrew

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