# Generalized Noether Theorem for Gauss-Bonnet Cosmology

## TL;DR

This paper applies generalized Noether's theorem to Gauss-Bonnet gravity models, deriving specific forms of the function $f(R,\, ext{G})$ that admit conserved quantities and are relevant for accelerated cosmological expansion.

## Contribution

It introduces polynomial and product forms of $f(R, ext{G})$ in Gauss-Bonnet gravity with conserved quantities, expanding the understanding of symmetries in modified gravity theories.

## Key findings

- Derived specific polynomial and product forms of $f(R, ext{G})$.
- Identified only time translational symmetry in these models.
- Confirmed energy conditions are consistent with conservation laws.

## Abstract

Generalized Noether's theory is a useful method for researching the modified gravity theories about the conserved quantities and symmetries. A generally Gauss-Bonnet gravity $f(R,\mathcal{G})$ theory was proposed as an alternative gravity model. Through the generalized Noether symmetry, polynomial and product forms of the $f(R,\mathcal{G})$ theory with corresponding conserved quantities and symmetries are researched. Then suitable general forms of the polynomial form $f(R,\mathcal{G}) \!=\! k_1 R^n + (6)^{\frac{n}{2}}(-1)^{n+1} k_1 \mathcal{G}^{\frac{n}{2}}$ and the product form $f(R,\mathcal{G}) \!=\! k ( R / \sqrt{\mathcal{G}} )^n \mathcal{G}$ are found out, to contain the solution of accelerated expansion cosmology. Both forms of $f(R,\mathcal{G})$ concerned in this paper only possess time translational symmetry. And energy condition of these solutions are also checked. To some extent, the consistency of conservation of symmetry and energy condition is demonstrated. For the specific form of different $n$, it needs further detailed study. Noting that, the corresponding conserved quantities are both zero, and the only conservation relation is conservation of energy.