http://arxiv.org/abs/1903.11743
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.
E. Colgáin
Fri, 29 Mar 19
56/78
Comments: 9 pages, my first foray into astro-ph, feedback welcome
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