CosmoCoffee

Hello,

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

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).