The Pantheon+ Analysis: Dependence of Cosmological Constraints on
  Photometric-Zeropoint Uncertainties of Supernova Surveys
  Type Ia supernovae (SNe Ia) measurements of the Hubble constant, H$_0$, the
cosmological mass density, $\Omega_M$, and the dark energy equation-of-state
parameter, $w$, rely on numerous SNe surveys using distinct photometric systems
across three decades of observation. Here, we determine the sensitivities of
the upcoming SH0ES+Pantheon+ constraints on H$_0$, $\Omega_M$, and $w$ to
unknown systematics in the relative photometric zeropoint calibration between
the 17 surveys that comprise the Pantheon+ supernovae data set. Varying the
zeropoints of these surveys simultaneously with the cosmological parameters, we
determine that the SH0ES+Pantheon+ measurement of H$_0$ is robust against
inter-survey photometric miscalibration, but that the measurements of
$\Omega_M$ and $w$ are not. Specifically, we find that miscalibrated
inter-survey systematics could represent a source of uncertainty in the
measured value of H$_0$ that is no larger than $0.2$ km s$^{-1}$ Mpc$^{-1}$.
This modest increase in H$_0$ uncertainty could not account for the $7$ km
s$^{-1}$ Mpc$^{-1}$ "Hubble Tension" between the SH0ES measurement of H$_0$ and
the Planck $\Lambda$CDM-based inference of H$_0$. However, we find that the
SH0ES+Pantheon+ best-fit values of $\Omega_M$ and $w$ respectively slip, to
first order, by $0.04$ and $-0.17$ per $25$ mmag of inter-survey calibration
uncertainty, underscoring the vital role that cross-calibration plays in
accurately measuring these parameters. Because the Pantheon+ compendium
contains many surveys that share low-$z$ Hubble Flow and Cepheid-paired SNe,
the SH0ES+Pantheon+ joint constraint of H$_0$ is robust against inter-survey
photometric calibration errors, and such errors do not represent an impediment
to jointly using SH0ES+Pantheon+ to measure H$_0$ to 1% accuracy.
