Dillon Brout tells us about the recent Pantheon+ supernovae catalogue and cosmology results. The cosmology results are excellent, including a factor of two improvement in the “figure of merit” compared to the previous Pantheon result (essentially a halving of error bars).

However, the results aren’t going to help anyone looking for a clue for a source of new physics. The supernovae themselves appear to follow the ΛCDM model very closely. If one anchors them to Planck, or to the SH0ES Cepheids, either way, one finds tight constraints on beyond ΛCDM parameters like an equation of state “w” or evolution of an equation of state “w_a”.

There is of course the baffling Hubble tension among all of this, and that is very clearly visible here. Both the Planck+Pantheon and the SH0ES+Pantheon results match up with ΛCDM, but at different values of H0. Any solution to the H0 tension that involves beyond ΛCDM evolution in the late-universe appears to be heavily constrained.

The most interesting part of this talk (for me) was actually the introduction in the answer to “what needed to be done before this analysis could happen” (in fact, this makes up the largest portion of the talk!). Dillon goes into quite a bit of detail about an earlier paper he wrote with Dan Scolnic, examining the affects of dust on supernovae observations. It appears that three of the most important mysteries in SN analysis were all explainable by the same dust affect and Dillon explains why here.

Dillon: https://djbrout.github.io/
Pantheon+ cosmology paper: https://arxiv.org/abs/2202.04077
Effects of dust on supernovae paper: https://arxiv.org/abs/2004.10206