Speaker
Description
I will present an end-to-end exploration of the simplest modified gravitational theory in Jordan-Brans-Dicke (JBD) gravity, from an analytical and numerical description of the background expansion and linear perturbations, to the nonlinear regime captured with a hybrid suite of $N$-body simulations, to the parameter constraints from existing cosmological probes. In the analysis, the nonlinear corrections to the matter power spectrum due to baryons, massive neutrinos, and modified gravity are simultaneously modeled and propagated in the cosmological analysis for the first time. I will show how the uncertainty in the gravitational theory alleviates the $S_8$ tension between the joint (3$\times$2pt) dataset of weak gravitational lensing tomography and overlapping redshift-space galaxy clustering from the Kilo Degree Survey $\times$ 2-degree Field Lensing Survey and the cosmic microwave background (CMB) dataset of Planck, and the extent to which it alleviates the tension between the local measurement of the Hubble constant and that inferred by Planck. Despite the alleviation of $S_8$ and $H_0$ tensions, I will show that there is no substantial model selection preference for JBD gravity relative to ΛCDM. I will further discuss how the uncertainty in the underlying gravitational theory complicates future inferences of small-scale physics from the CMB.
