Modified gravity in the presence of matter creation: scenario for the late Universe

TL;DR

This paper proposes a modified gravity model with matter creation to explain late Universe evolution, aiming to resolve the Hubble tension by fitting observational data within a consistent theoretical framework.

Contribution

It introduces a novel $f(R)$ gravity model incorporating matter creation, providing a new approach to reconcile Planck data with late Universe observations.

Findings

The model can reconcile Planck Hubble measurements with late Universe data.

The scalar field potential determines the current vacuum energy density.

Constraints on matter creation parameters eliminate tachyonic instabilities.

Abstract

We consider a dynamic scenario for characterizing the late Universe evolution, aiming to mitigate the Hubble tension. Specifically, we consider a metric $f(R)$ gravity in the Jordan frame which is implemented to the dynamics of a flat isotropic Universe. This cosmological model incorporates a matter creation process, due to the time variation of the cosmological gravitational field. We model particle creation by representing the isotropic Universe (specifically, a given fiducial volume) as an open thermodynamic system. The resulting dynamical model involves four unknowns: the Hubble parameter, the non-minimally coupled scalar field, its potential, and the energy density of the matter component. We impose suitable conditions to derive a closed system for these functions of the redshift. In this model, the vacuum energy density of the present Universe is determined by the scalar field potential, in line with the modified gravity scenario. Hence, we construct a viable model, determining the form of the $f(R)$ theory a posteriori and appropriately constraining the phenomenological parameters of the matter creation process to eliminate tachyon modes. Finally, by analyzing the allowed parameter space, we demonstrate that the Planck evolution of the Hubble parameter can be reconciled with the late Universe dynamics, thus alleviating the Hubble tension.