# General Cosmography Model with Spatial Curvature

## TL;DR

This study uses cosmography with various approximants to constrain spatial curvature, finding weak evidence for a closed universe and suggesting that considering curvature can slightly alleviate the Hubble tension.

## Contribution

It introduces the use of Padé and Taylor series approximants in cosmography to better constrain spatial curvature and assess its impact on the Hubble tension.

## Key findings

- Weak evidence for a closed universe from current data.
- Hubble constant $H_0$ is anti-correlated with spatial curvature and sound horizon.
- Introducing curvature can slightly relax the Hubble tension.

## Abstract

The cosmographic approach is adopted to determine the spatial curvature (i.e., $\Omega_K$) combining the latest released cosmic chronometers data (CC), the Pantheon sample of type Ia supernovae observations, and the baryon acoustic oscillation measurements. We use the expanded transverse comoving distance $D_M(z)$ as a basic function for deriving $H(z)$ and the other cosmic distances. In this scenario, $\Omega_K$ can be constrained only by CC data. To overcome the convergence issues at high-redshift domains, two methods are applied: the Pad\'{e} approximants and the Taylor series in terms of the new redshift $y=z/(1+z)$. Adopting the Bayesian evidence, we find that there is positive evidence for the Pad\'{e} approximant up to order ($2,2$) and weak evidence for the Taylor series up to 3-rd order against $\Lambda\text{CDM}+\Omega_K$ model. The constraint results show that a closed universe is preferred by the present observations under all the approximants used in this study. And the tension level of the Hubble constant $H_0$ is less than $2\sigma$ significance between different approximants and the local distance ladder determination. For each assumed approximant, $H_0$ is anti-correlated with $\Omega_K$ and the sound horizon at the end of the radiation drag epoch, which indicates that the $H_0$ tension problem can be slightly relaxed by introducing $\Omega_K$ or any new physics which can reduce the sound horizon in the early universe.