Implications of a transition in the dark energy equation of state for the <i>H</i>₀ and σ₈ tensions

Abstract

We explore the implications of a rapid appearance of dark energy between the\nredshifts ($z$) of one and two on the expansion rate and growth of\nperturbations. Using both Gaussian process regression and a parameteric model,\nwe show that this is the preferred solution to the current set of low-redshift\n($z&lt;3$) distance measurements if $H_0=73~\\rm km\\,s^{-1}\\,Mpc^{-1}$ to within\n1\\% and the high-redshift expansion history is unchanged from the $\\Lambda$CDM\ninference by the Planck satellite. Dark energy was effectively non-existent\naround $z=2$, but its density is close to the $\\Lambda$CDM model value today,\nwith an equation of state greater than $-1$ at $z&lt;0.5$. If sources of\nclustering other than matter are negligible, we show that this expansion\nhistory leads to slower growth of perturbations at $z&lt;1$, compared to\n$\\Lambda$CDM, that is measurable by upcoming surveys and can alleviate the\n$\\sigma_8$ tension between the Planck CMB temperature and low-redshift probes\nof the large-scale structure.\n