Hi,
I'm trying to modify CAMB and
I'm a little bit confused about the variables used in camb respect, for
example, to cmbfast.
In particular:
CMBFAST uses \eta, \dot{\eta}, \dot{h} and \alpha=\dot{h}+6\dot{\eta}
and write the Einstein equations for these quantities (eq. 21a21b21d in notation of MaBertschinger)
CAMB uses: etak=k\eta, Z=\dot{h}/2k and \sigma=(0.5*\dot{h}+3\dot{\eta})/k
and write the Einstein equations for these quantities,
but these are 3 variables and
I think I should consider another one and write the relative
Einstein equation: in other words, I can't find an equation for
the shear (corresponding to eq.21d in MaBertshinger).
Could you help me?
Thanks in advance
Paolo
camb vs cmbfast output

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 Joined: February 26 2008
 Affiliation: University of California, Irvine

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Re: camb vs cmbfast output
The metric shear is just a derived variable in CAMB, it is not propagated (the evolution eqn is given in e.g. 6.71 of my thesis and is equivalent to M&B  I think what they call shear is what I call anisotropic stress).