Recasting $H_0$ tension as $Omega_m$ tension at low $z$. (arXiv:1903.11743v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Colgain_E/0/1/0/all/0/1">Eoin Ó Colgáin</a>
Inspired by the recent observation that local measurements of the Hubble
constant $H_0$ and the Planck CMB value based on $Lambda$CDM show a
discrepancy at $4.4 , sigma$ cite{Riess:2019cxk}, we study $Lambda$CDM at
low redshift. Concretely, we expand $Lambda$CDM perturbatively at small $z$
and perform a two-parameter fit of the distance modulus to Pantheon data for a
running cut-off $z_{textrm{max}} leq 0.3$. Moving beyond the Hubble constant
$H_0$, we shift focus to matter density $Omega_m$, noting foremost that its
best-fit value is sensitive to the cut-off. For $z_{textrm{max}} > 0.1$, the
uncertainties in $Omega_m$ decrease and the difference with the Planck value
$Omega_m = 0.315 pm 0.007$ becomes noticeable. In particular, in the range
$0.1 leq z_{textrm{max}} < 0.16$, the best-fit value is negative and the
discrepancy with the Planck value approaches $4 , sigma$. Restricting to
$z_{textrm{max}}$ where the best-fit value is positive and physical, the
discrepancy is reduced to $3.1 , sigma$. For high-energy theorists, the
analysis appears to support the de Sitter Swampland conjecture.
Inspired by the recent observation that local measurements of the Hubble
constant $H_0$ and the Planck CMB value based on $Lambda$CDM show a
discrepancy at $4.4 , sigma$ cite{Riess:2019cxk}, we study $Lambda$CDM at
low redshift. Concretely, we expand $Lambda$CDM perturbatively at small $z$
and perform a two-parameter fit of the distance modulus to Pantheon data for a
running cut-off $z_{textrm{max}} leq 0.3$. Moving beyond the Hubble constant
$H_0$, we shift focus to matter density $Omega_m$, noting foremost that its
best-fit value is sensitive to the cut-off. For $z_{textrm{max}} > 0.1$, the
uncertainties in $Omega_m$ decrease and the difference with the Planck value
$Omega_m = 0.315 pm 0.007$ becomes noticeable. In particular, in the range
$0.1 leq z_{textrm{max}} < 0.16$, the best-fit value is negative and the
discrepancy with the Planck value approaches $4 , sigma$. Restricting to
$z_{textrm{max}}$ where the best-fit value is positive and physical, the
discrepancy is reduced to $3.1 , sigma$. For high-energy theorists, the
analysis appears to support the de Sitter Swampland conjecture.
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