Speaker
Description
We study Brans-Dicke gravity with a cosmological constant and cold dark matter (BD-$\Lambda$CDM hereafter). This theory is the first historical attempt to extend Einstein's General Relativity by promoting the Newtonian coupling constant $G_N$ to a dynamical one $G(t)$. We present the background and the perturbation equations, which allows us to test the theoretical predictions with a complete and updated data string, formed by: CMB+BAO+LSS+$H(z)$+SNIa. Additionally, we contemplate the possibility of including alternative data in order to cover a wide variety of different scenarios. The BD-$\Lambda$CDM turns out to be observationally favored as compared to the concordance model (GR-$\Lambda$CDM). We pay special attention to the ability of the BD-$\Lambda$CDM model to smooth out not only the $H_0$-tension but also the $\sigma_8$ one. An exhaustive study can be found in arXiv:2006.04273. Due to the possible connection with the running vacuum models (RVM's) (see arXiv:2102.12758 and references therein), where a time-evolving vacuum energy density in the context of QFT is considered, we deem it is worthwhile to also present the background and the perturbation equations, as well as, the performance, of this kind of models, when they are put in the light of the observational data.
