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arXiv · 2511.06755

Redshift-Frame Systematics and Their Impact on the Hubble Constant from Pantheon+ Supernovae

Said Laaroua
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Abstract

We present a full-sky, covariance-weighted analysis of redshift-frame transformations in the Pantheon+ Type Ia supernova sample to assess their impact on local measurements of the Hubble constant. Using 1,543 supernovae with heliocentric and CMB-frame redshifts, we study the residual field delta z = zCMB - zHEL, which traces the Solar System's kinematic correction. We recover the expected monopole = (-3.8 +/- 0.1) x 10^-4 and a dipole amplitude A = (1.5 +/- 0.1) x 10^-3 aligned within 1 degree of the CMB dipole, confirming internal consistency. Propagating these residuals through the full Pantheon+ covariance matrix yields a negligible shift in H0, at the <= 2% level of the current tension, placing a quantitative upper bound on redshift-frame systematics.

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Said Laaroua. 2025-11-10. Redshift-Frame Systematics and Their Impact on the Hubble Constant from Pantheon+ Supernovae. https://doi.org/10.33232/001c.159558

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