Sibling Rivalry: Thermonuclear Diversity and the Hubble Tension

Abstract

Homogeneity is the hallmark of standard candle-based cosmology investigations. Thermonuclear supernovae (Type-Ia, SNeIa) violate this essential requirement if they develop along multiple evolutionary pathways. In this work, the impact of thermonuclear diversity on cosmological parameter constraints is quantified using Pantheon+, one of the largest ensembles of SNeIa compiled to probe cosmology to date. Evidence of diversity is encoded in supernova light curves. Pantheon+ is shown to be diverse, with features indicative of multiple thermonuclear sub-classes. Diversity-driven systematic effects have been quantified on a supernova-by-supernova basis; event selections based on light curve-derived metrics were subsequently used to characterize diversity-dependent trends and mitigate their impact. A "diversity free" estimate of the Hubble-Lema\^{i}tre parameter, $H_0$=$67.5\pm3.5$ km s$^{-1}$ Mpc$^{-1}$ (68\% C.L.), was obtained by reanalyzing Pantheon+. The Hubble Tension, an apparent disparity between early- and late-Universe determinations of $H_0$, is eased from $\sim$$5\sigma$ to $<$$1\sigma$ after accounting for the diverse thermonuclear scenarios that govern SNeIa. A strategy for precise determination of $H_0$, dominated by statistical rather than systematic uncertainties, is also presented.