Pantheon update on a model-independent analysis of cosmological supernova data

Abstract

We present an update of our previous work, necessitated by availability of a significantly improved dataset. The work is a model-independent analysis of the cosmological supernova (type Ia) data, where function families are fit to the data in form of luminosity distance as function of redshift, that is, d(L)(z); and subsequently time-derivatives of the scale function a(t) are analytically derived, but as functions of z, without making assumptions about the theory of gravity or the contents of the Universe. This gives, e.g. the redshift value at which the Universe goes over from deceleration to acceleration, as z = 0.54 +/- 0.04 for a flat Universe. In the update, we switch to a more modern fit criterion and also take into account the uncertainty in the calibration of the SNIa luminosities. If a theory of gravity is assumed, our results allow determination of the density of the Universe as function of z, from which conclusions about the contents of the Universe can be drawn. We update the previous work's result where this was done for Einstein gravity, finding a lower-limit on the dark energy (DE) fraction, omega(DE) > 0.46; and here we do this also for Starobinsky gravity, where we can find a Starobinsky parameter that can eliminate the need for DE.