An Accelerating Universe without Lambda: Delta~Gravity Using Monte Carlo

Abstract

A gravitational field model based on two symmetric tensors, $g_{\mu \nu}$ and $\tilde{g}_{\mu \nu}$, is studied, using a Markov Chain Monte Carlo (MCMC) analysis with the most updated catalog of SN-Ia. In this model, new matter fields are added to the original matter fields, motivated by an additional symmetry ($\tilde{\delta}$~symmetry). We call them $\tilde{\delta}$ matter fields. This theory predicts an accelerating Universe without the need to introduce a cosmological constant $\Lambda$ by hand in the equations. We obtained a very good fit to the SN-Ia Data, and with this, we found the two free parameters of the theory called $C$ and $L_2$. With these values, we have fixed all the degrees of freedom in the model. The last $H_0$ local value measurement is in tension with the CMB Data from Planck. Based on an absolute magnitude $M_V = -19.23$ for the SN, Delta Gravity finds $H_0$ to be $74.47\pm 1.63$ km/(s Mpc). This value is in concordance with the last measurement of the $H_0$ local value, $73.83\pm 1.48$ km/(s Mpc).