First Cosmology Results Using Type Ia Supernovae from the Dark Energy
  Survey: Effects of Chromatic Corrections to Supernova Photometry on
  Measurements of Cosmological Parameters
  Calibration uncertainties have been the leading systematic uncertainty in
recent analyses using type Ia Supernovae (SNe Ia) to measure cosmological
parameters. To improve the calibration, we present the application of Spectral
Energy Distribution (SED)-dependent "chromatic corrections" to the supernova
light-curve photometry from the Dark Energy Survey (DES). These corrections
depend on the combined atmospheric and instrumental transmission function for
each exposure, and they affect photometry at the 0.01 mag (1%) level,
comparable to systematic uncertainties in calibration and photometry. Fitting
our combined DES and low-z SN Ia sample with Baryon Acoustic Oscillation (BAO)
and Cosmic Microwave Background (CMB) priors for the cosmological parameters
$\Omega_{\rm m}$ (the fraction of the critical density of the universe
comprised of matter) and w (the dark energy equation of state parameter), we
compare those parameters before and after applying the corrections. We find the
change in w and $\Omega_{\rm m}$ due to not including chromatic corrections are
-0.002 and 0.000, respectively, for the DES-SN3YR sample with BAO and CMB
priors, consistent with a larger DES-SN3YR-like simulation, which has a
w-change of 0.0005 with an uncertainty of 0.008 and an $\Omega_{\rm m}$ change
of 0.000 with an uncertainty of 0.002 . However, when considering samples on
individual CCDs we find large redshift-dependent biases (approximately 0.02 in
distance modulus) for supernova distances.
