Effect of polarization in extra-radiation models

Use of Cobaya. camb, CLASS, cosmomc, compilers, etc.
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Jose Lozano
Posts: 19
Joined: June 27 2023
Affiliation: Universidad Nacional Autónoma de México

Effect of polarization in extra-radiation models

Post by Jose Lozano »


I'm running a quintessence dark energy model with extra radiation before recombination. I'm compiling such a model with full CMB ( TT+TE+EE+LowE+lensing) in CosmoMC and the value of H0 seems to decrease. In LCDM, I notice that the value of H0 also decreases by adding some extra-radiation in Neff. However, as far as I know, adding extra radiation before the recombination makes H0 larger. Does polarization play an important roll in this case? Or should I modify the polarization part in CAMB/CosmoMC?

I'm looking forward to your kind reply,

Jose Lozano
Antony Lewis
Posts: 1964
Joined: September 23 2004
Affiliation: University of Sussex

Re: Effect of polarization in extra-radiation models

Post by Antony Lewis »

If you only allow Neff > 3.044 then yes it should normally increase H0 at fixed Planck data in LCDM+Neff model (faster expansion -> shorter time to recombination -> smaller sound horizon -> smaller comoving angular diameter distance for same observed peak position). But if you allow smaller values of Neff, Planck 2018 tends to peak at Neff a bit below 3, since high neff does not fit the shape of the CMB power spectra well (even with just TT+lowE).
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