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tokens: (Linder 2008 ). 3.4. Growing <italic>ν</italic> Mass Growing neutrino mass models, wherein the mass of the neutrino ( m ν ) increases with time and stops the dynamical evolution of the dark-energy scalar field are invoked to solve the cosmological coincidence problem, i.e., the problem that the present-day matter density and density of Λ are similar order of magnitude despite their different dependence on the scale factor (Fardon et al. 2004 ; Wetterich 2007 ). The combined dark sector (scalar field plus neutrinos) energy density (where a = 1/(1 + z )) is given by where Ω ds = 1 − Ω M is the present-day dark-energy density. The scale factor at which the neutrinos become nonrelativistic, is given by preserving continuity between the early and late-time terms (i.e., setting Equations ( 14 ) and ( 15 ) at a = a t ). The two free parameters are the early dark-energy density Ω e and the neutrino density Ω ν . The normalized Hubble parameter for this model is given by 3.5. Dark-energy Transitions at Low Redshift Mortonson et al. ( 2009 ) proposes models with large fluctuations in the dark-energy equation of state at low redshifts, typically z ≲ 0.02, that induce step-like transitions in the H ( z ). Such changes are hidden from constraints coming from Hubble flow SNe Ia (as even the lowest redshift SNe can typically be at z > z t ), but calibrators offer an additional restriction. Step-like responses in H ( z ) also evade several model-independent constraints, as they often assume smoothness of H ( z ). Phenomenologically, we can write the first Friedmann equation in these models aswhereIn this definition, z t , and δ are the position, width, and amplitude of the transition, respectively. In particular, δ = 0 corresponds to the standard ΛCDM . Hence, this model has three free parameters at a given fixed z t : , and δ . The observed Hubble constant is . In this work, we either assume z t = 0.02 or z t = 0.1; the former case motivated by Mortonson et al. ( 2009 ) and the latter case motivated so we can use all the low- z SNe at z ≈ 0.1. The adopted priors for and are equivalent to the priors shown on Table 1 for H 0 and Ω M . The difference in notation highlights the fact that and cannot be interpreted as the observed Hubble constant and the dark-matter density at redshift zero in these models (see Mortonson et al. 2009 ). 3.6. Cosmographic Expansion Along with the different dark-energy models described above, we also look into a more model-independent method, by expanding the expression for H ( z ) as a Taylor series in a cosmographic approach (for e.g., Arendse et al. 2019a , 2019b ; Feeney et al. 2019 ; Macaulay et al. 2019 ). Expanding H ( z ), we getwhere , 2 and . 4. Results In this section we present the results of fitting the different dark-energy models described in Section 4.1 to the combined calibrator and Hubble flow SNe Ia. We also discuss the impact of the systematics covariance matrix on the inferred value of H 0 in Section 4.2 .