Unimodular Theory of Gravity in Light of the Latest Cosmological Data

TL;DR

This paper explores unimodular gravity's implications in cosmology using recent observational data, finding deviations from standard general relativity and providing updated estimates for the Hubble constant.

Contribution

It introduces a model of unimodular gravity fitted with latest cosmological data, estimating the key parameter  and addressing the Hubble constant discrepancy.

Findings

Best-fit  parameter is 6.23 b1 0.5, deviating from 6.

Hubble constant estimates are 70.7 b1 4.1 and 69.24 b1 0.90 km/s/Mpc from different data sets.

Combined data yields H0 as 70.57 b1 0.56 km/s/Mpc.

Abstract

The unimodular theory of gravity is an alternative perspective to traditional Einstein's general relativity and opens new possibilities for exploring its implications in cosmology. In this paper, we investigate the unimodular gravity (UG) with the latest cosmological data from the Pantheon sample of Type Ia supernovae (SN), Baryon Acoustic Oscillations (BAO), and the observational H(z) data from Differential Age method (DA). We consider a model consisting of a generalized cosmological constant with radiation and dark matter. The considered theory respects only unimodular coordinate transformations. We fit our model with low-redshift data from SN and DA and determine the value of parameter $\xi$ of the theory. We find the best-fit value of parameter $\xi =6.23 \pm 0.5$; which deviates from 6, for which the theory becomes the standard general theory of relativity. We further study the Hubble constant problem by combining the SN and DA data with BAO data. We observe deviation in the value of $H_0$ from the standard $\Lambda$CDM model. We obtain $H_0$ as $70.7 \pm 4.1 \ \mbox{Km s}^{-1} \mbox{Mpc} ^{-1}$ and $69.24 \pm 0.90 \ \mbox{Km s}^{-1} \mbox{Mpc} ^{-1}$ from supernovae data and BAO data, respectively in unimodular gravity. Combining the BAO data with SN+DA data set, we obtain $H_0$ as $70.57 \pm 0.56 \ \mbox{Km s}^{-1} \mbox{Mpc} ^{-1}$.