# Nonsingular universe in massive gravity's rainbow

## TL;DR

This paper explores how combining massive gravity with gravity's rainbow can potentially eliminate the initial singularity in the universe's evolution, offering a nonsingular cosmological model.

## Contribution

It introduces a novel framework integrating massive gravity and gravity's rainbow to address the early universe singularity problem.

## Key findings

- Massive gravity alone does not remove the Big Bang singularity.
- Gravity's rainbow modifies the cosmological equations.
- The combined approach can eliminate the initial singularity.

## Abstract

One of the fundamental open questions in cosmology is whether we can regard the universe evolution without singularity like a Big Bang or a Big Rip. This challenging subject stimulates one to regard a nonsingular universe in the far past with an arbitrarily large vacuum energy. Considering the high energy regime in the cosmic history, it is believed that Einstein gravity should be corrected to an effective energy dependent theory which could be acquired by gravity's rainbow. On the other hand, employing massive gravity provided us with solutions to some of the long standing fundamental problems of cosmology such as cosmological constant problem and self acceleration of the universe. Considering these aspects of gravity's rainbow and massive gravity, in this paper, we initiate studying FRW cosmology in the massive gravity's rainbow formalism. At first, we show that although massive gravity modifies the FRW cosmology, but it does not itself remove the big bang singularity. Then, we generalize the massive gravity to the case of energy dependent spacetime and find that massive gravity's rainbow can remove the early universe singularity. We bring together all the essential conditions for having a nonsingular universe and the effects of both gravity's rainbow and massive gravity generalizations on such criteria are determined.