Determining the Hubble Constant without the Sound Horizon Scale: Measurements from CMB Lensing. (arXiv:2007.04007v2 [astro-ph.CO] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Baxter_E/0/1/0/all/0/1">Eric J. Baxter</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sherwin_B/0/1/0/all/0/1">Blake D. Sherwin</a>
Measurements of the Hubble constant, $H_0$, from the cosmic distance ladder
are currently in tension with the value inferred from Planck observations of
the CMB and other high redshift datasets if a flat $Lambda$CDM cosmological
model is assumed. One of the few promising theoretical resolutions of this
tension is to invoke new physics that changes the sound horizon scale in the
early universe; this can bring CMB and BAO constraints on $H_0$ into better
agreement with local measurements. In this paper, we discuss how a measurement
of the Hubble constant can be made from the CMB without using information from
the sound horizon scale, $r_s$. In particular, we show how measurements of the
CMB lensing power spectrum can be used to place interesting constraints on
$H_0$ when combined with measurements of either supernovae or galaxy weak
lensing, which constrain the matter density parameter. The constraints arise
from the sensitivity of the CMB lensing power spectrum to the horizon scale at
matter-radiation equality (in projection); this scale could have a different
dependence on new physics than the sound horizon. From an analysis of current
CMB lensing data from Planck and Pantheon supernovae with conservative external
priors, we derive an $r_s$-independent constraint of $H_0 = 73.5pm 5.3$
km/s/Mpc. Forecasts for future CMB surveys indicate that improving constraints
beyond an error of $sigma(H_0) = 3$ km/s/Mpc will be difficult with CMB
lensing, although applying similar methods to the galaxy power spectrum may
allow for further improvements.
Measurements of the Hubble constant, $H_0$, from the cosmic distance ladder
are currently in tension with the value inferred from Planck observations of
the CMB and other high redshift datasets if a flat $Lambda$CDM cosmological
model is assumed. One of the few promising theoretical resolutions of this
tension is to invoke new physics that changes the sound horizon scale in the
early universe; this can bring CMB and BAO constraints on $H_0$ into better
agreement with local measurements. In this paper, we discuss how a measurement
of the Hubble constant can be made from the CMB without using information from
the sound horizon scale, $r_s$. In particular, we show how measurements of the
CMB lensing power spectrum can be used to place interesting constraints on
$H_0$ when combined with measurements of either supernovae or galaxy weak
lensing, which constrain the matter density parameter. The constraints arise
from the sensitivity of the CMB lensing power spectrum to the horizon scale at
matter-radiation equality (in projection); this scale could have a different
dependence on new physics than the sound horizon. From an analysis of current
CMB lensing data from Planck and Pantheon supernovae with conservative external
priors, we derive an $r_s$-independent constraint of $H_0 = 73.5pm 5.3$
km/s/Mpc. Forecasts for future CMB surveys indicate that improving constraints
beyond an error of $sigma(H_0) = 3$ km/s/Mpc will be difficult with CMB
lensing, although applying similar methods to the galaxy power spectrum may
allow for further improvements.
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