Presentation #334.05 in the session Dark Matter and Dark Energy.
Type Ia supernovae (SN Ia) are more nearly standard candles when measured in the near-infrared (NIR) than in the optical. With this motivation, from 2012-2017 we embarked on the RAISIN (an anagram of SN IA in the NIR) program with the Hubble Space Telescope to obtain rest-frame NIR light curves for a cosmologically distant sample of 37 SN Ia (0.2 < z < 0.7) discovered by Pan-STARRS and the Dark Energy Survey. By comparing higher-z HST data with 43 SN Ia at z < 0.1 observed in the NIR by the Carnegie Supernova Project, we construct a Hubble diagram exclusively from NIR observations to pursue a unique avenue to constrain the dark energy equation of state parameter, w. We analyze the dependence of the full set of Hubble residuals on the SN Ia host galaxy mass and find Hubble residual steps of size ~0.08-0.12 mag with 2- to 3-σ significance depending on the method and step location used. Combining our NIR sample with Cosmic Microwave Background (CMB) constraints, we find 1 + w = -0.04 ± 0.12 (statistical+systematic errors). The largest systematic errors are the redshift-dependent SN selection biases and the properties of the NIR mass step. We also use these data to measure Ho = 75.4 ± 2.4 km s-1 Mpc-1 from stars with geometric distance calibration in the hosts of 8 SN Ia observed in the NIR versus Ho= 65.9 ± 3.4 km s-1 Mpc-1 using an inverse distance ladder approach tied to Planck. Using optical data we find 1 + w= -0.01 ± 0.09 and with optical and NIR data combined, we find 1 + w = 0.03 ± 0.08; these shifts of up to ~0.07 in w could point to inconsistency in the optical versus NIR SN models. There will be many opportunities to improve this NIR measurement and better understand systematic uncertainties through larger low-z samples, new light-curve models, calibration improvements, and eventually by building large high-z samples from the Roman Space Telescope.