Updated fundamental constant constraints from Planck 2018 data and possible relations to the Hubble tension. (arXiv:1912.03986v2 [astro-ph.CO] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Hart_L/0/1/0/all/0/1">Luke Hart</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chluba_J/0/1/0/all/0/1">Jens Chluba</a>

We present updated constraints on the variation of the fine structure
constant, $alpha_{rm EM}$, and effective electron rest mass, $m_{rm e}$,
during the cosmological recombination era. These two fundamental constants
directly affect the ionization history at redshift $zsimeq 1100$ and thus
modify the temperature and polarisation anisotropies of the cosmic microwave
background (CMB) measured precisely with {it Planck }. The constraints on
$alpha_{rm EM}$ tighten slightly due to improved {it Planck} 2018
polarisation data but otherwise remain similar to previous CMB analysis.
However, a comparison with the 2015 constraints reveals a mildly discordant
behaviour for $m_{rm e}$, which from CMB data alone is found below its local
value. Adding baryon acoustic oscillation data brings $m_{rm e}$ back to the
fiducial value, $m_{rm e}=(1.0078pm0.0067) m_{rm e,0}$, and also drives the
Hubble parameter to $H_0=69.1pm 1.2$ [in units of ${rm km , s^{-1} ,
Mpc^{-1} }$]. Further adding supernova data yields $m_{rm e}=(1.0190pm0.0055)
m_{rm e,0}$ with $H_0=71.24pm0.96$. We perform several comparative analyses
using the latest cosmological recombination calculations to further understand
the various effects. Our results indicate that a single-parameter extension
allowing for a slightly increased value of $m_{rm e}$ ($simeq 3.5sigma$
above $m_{rm e,0}$) could play a role in the Hubble tension.

We present updated constraints on the variation of the fine structure
constant, $alpha_{rm EM}$, and effective electron rest mass, $m_{rm e}$,
during the cosmological recombination era. These two fundamental constants
directly affect the ionization history at redshift $zsimeq 1100$ and thus
modify the temperature and polarisation anisotropies of the cosmic microwave
background (CMB) measured precisely with {it Planck }. The constraints on
$alpha_{rm EM}$ tighten slightly due to improved {it Planck} 2018
polarisation data but otherwise remain similar to previous CMB analysis.
However, a comparison with the 2015 constraints reveals a mildly discordant
behaviour for $m_{rm e}$, which from CMB data alone is found below its local
value. Adding baryon acoustic oscillation data brings $m_{rm e}$ back to the
fiducial value, $m_{rm e}=(1.0078pm0.0067) m_{rm e,0}$, and also drives the
Hubble parameter to $H_0=69.1pm 1.2$ [in units of ${rm km , s^{-1} ,
Mpc^{-1} }$]. Further adding supernova data yields $m_{rm e}=(1.0190pm0.0055)
m_{rm e,0}$ with $H_0=71.24pm0.96$. We perform several comparative analyses
using the latest cosmological recombination calculations to further understand
the various effects. Our results indicate that a single-parameter extension
allowing for a slightly increased value of $m_{rm e}$ ($simeq 3.5sigma$
above $m_{rm e,0}$) could play a role in the Hubble tension.

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