# Fine Tuning Problem of the Cosmological Constant in a Generalized Randall-Sundrum Model

## TL;DR

This paper proposes a generalized Randall-Sundrum model with two branes that naturally produces a tiny effective cosmological constant and explains the universe's transition from deceleration to acceleration as an extra-dimensional effect.

## Contribution

It introduces a new brane world scenario with positive tensions that solves the cosmological constant fine-tuning problem and aligns with cosmic data.

## Key findings

- Achieves an effective cosmological constant of order 10^{-124}.
- Predicts a universe evolution from deceleration to acceleration.
- Matches cosmic chronometers dataset for Hubble parameter evolution.

## Abstract

To solve the cosmological constant fine tuning problem, we investigate a $(n+1)$-dimensional generalized Randall-Sundrum brane world scenario with two $(n-1)$-branes instead of two 3-branes. Adopting an anisotropic metric ansatz, we obtain the positive effective cosmological constant $\Omega_{eff}$ of order $10^{-124}$ and only require a solution $\simeq50-80$. Meanwhile, both the visible and hidden branes are stable because their tensions are positive. Therefore, the fine tuning problem can be solved quite well. Furthermore, the Hubble parameter $H_{1}(z)$ as a function of redshift $z$ is in good agreement with cosmic chronometers dataset. The evolution of the universe naturally shifts from deceleration to acceleration. This demonstrates that the evolution of the universe is intrinsically an extra-dimensional phenomenon. It can be seen as a dynamic model of dark energy which is driven by the evolution of the extra dimensions on the brane.