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Power Spectra with CAMB

Posted: March 08 2018
by Joseph Wraga
I was going through the tutorial for CAMB ( ) and I notice the TT spectrum is shifted downward compared with the Planck 2015 results( ) . For example, the first peak in the demo is around 5300 [tex] \mu K^2[/tex], while for Planck the peak is around 5700 [tex] \mu K^2[/tex]. I notice the same thing when trying to compare the BB spectrum with the best fit values (third entry in the data set column in ... lary-data/ ). In both cases it seems multiplying the CAMB results by a constant factor would make them match the Planck observation, but I do not see why that is the case.

Re: Power Spectra with CAMB

Posted: March 09 2018
by Antony Lewis
The demo is just using some random parameters. Specifically it probably doesn't set a realistic value of A_s. Always check with print(pars) that everything is correct after setting values.

Power Spectra with CAMB

Posted: March 10 2018
by Joseph Wraga
Yes, that was the problem. Adjusting [tex] A_s[/tex] according to Planck (default value was slightly too small) makes the CAMB result match the best-fit model.
Thank you!