| Summary: | The unimodular theory of gravity is an alternative perspective to the traditional general relativity of Einstein and opens new possibilities for exploring its implications in cosmology. In this paper, we investigated Unimodular Gravity (UG) with the cosmological data from the Pantheon sample of Type Ia Supernovae (SNs) (2018), Baryon Acoustic Oscillations (BAOs), and the observational H(z) data from the Differential Age method (DA). We also used the Cosmic Microwave Background (CMB) distance priors from the Planck 2018 results. We considered a model consisting of a generalized cosmological constant, radiation, and a dark matter component along with normal matter. The considered theory respects only unimodular coordinate transformations. We first fit our model with low-redshift data from SNs and DA and determined the value of the model parameters <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>(</mo><mi>ξ</mi><mo>,</mo><mspace width="0.166667em"></mspace><msub><mi>H</mi><mn>0</mn></msub><mo>)</mo></mrow></semantics></math></inline-formula>. We found the best-fit value of parameter <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>ξ</mi><mo>=</mo><mn>6.03</mn><mo>±</mo><mn>0.40</mn></mrow></semantics></math></inline-formula>, which deviates slightly from 6, for which the theory becomes the standard general theory of relativity. We observed a small deviation in the value of the Hubble constant (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>H</mi><mn>0</mn></msub><mo>=</mo><mn>72.6</mn><mo>±</mo><mn>3.5</mn></mrow></semantics></math></inline-formula> km s<sup>−1</sup> Mpc<sup>−1</sup>) in the UG model compared with the standard <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mo>Λ</mo></semantics></math></inline-formula>CDM model (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>H</mi><mn>0</mn></msub><mo>=</mo><mn>72.2</mn><mo>±</mo><mn>1.2</mn></mrow></semantics></math></inline-formula> km s<sup>−1</sup> Mpc<sup>−1</sup>). Using the BAO + CMB constraint in the UG model, we obtained <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>H</mi><mn>0</mn></msub><mo>=</mo><mn>68.45</mn><mo>±</mo><mn>0.66</mn><mspace width="4pt"></mspace><mrow><mi>km</mi></mrow><mspace width="4pt"></mspace><msup><mrow><mi mathvariant="normal">s</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup><msup><mrow><mi>Mpc</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></semantics></math></inline-formula>, and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi>ξ</mi></semantics></math></inline-formula> is ∼6.029. For the combined datasets (SN + DA + BAO + CMB), the estimated <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>H</mi><mn>0</mn></msub><mo>=</mo><mn>69.01</mn><mo>±</mo><mn>0.60</mn><mspace width="4pt"></mspace><mrow><mi>km</mi></mrow><mspace width="4pt"></mspace><msup><mrow><mi mathvariant="normal">s</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup><mspace width="4pt"></mspace><msup><mrow><mi>Mpc</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></semantics></math></inline-formula> with <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>ξ</mi><mo>∼</mo></mrow></semantics></math></inline-formula>6.037, and in standard gravity, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>H</mi><mn>0</mn></msub><mo>=</mo><mn>68.25</mn><mo>±</mo><mn>0.40</mn><mspace width="4pt"></mspace><mrow><mi>km</mi></mrow><mspace width="4pt"></mspace><msup><mrow><mi mathvariant="normal">s</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup><mspace width="4pt"></mspace><msup><mrow><mi>Mpc</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></semantics></math></inline-formula>.
|
|---|