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Arxiv New Filter | Bookmarks & clubs | Arxiv ref/author:

Power Spectra with CAMB
 
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Joseph Wraga



Joined: 22 Feb 2018
Posts: 6
Affiliation: Drexel University

PostPosted: March 08 2018  Reply with quote

I was going through the tutorial for CAMB (http://camb.readthedocs.io/en/latest/CAMBdemo.html ) and I notice the TT spectrum is shifted downward compared with the Planck 2015 results( https://arxiv.org/pdf/1502.02114.pdf ) . For example, the first peak in the demo is around 5300 μK2, while for Planck the peak is around 5700 μK2. 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 http://irsa.ipac.caltech.edu/data/Planck/release_2/ancillary-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.
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Antony Lewis



Joined: 23 Sep 2004
Posts: 1332
Affiliation: University of Sussex

PostPosted: March 09 2018  Reply with quote

The demo is just using some random parameters. Specifically it probably doesn't set a realistic value of As. Always check with print(pars) that everything is correct after setting values.
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Joseph Wraga



Joined: 22 Feb 2018
Posts: 6
Affiliation: Drexel University

PostPosted: March 10 2018  Reply with quote

Yes, that was the problem. Adjusting As according to Planck (default value was slightly too small) makes the CAMB result match the best-fit model.
Thank you!
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