# Violation of Universal Lower Bound for the Shear Viscosity to Entropy Density Ratio in Dark Energy Dominated Accretion

## TL;DR

This paper investigates how dark energy influences the shear viscosity to entropy density ratio in accretion flows, challenging the universal lower bound suggested by string theory, and finds that dark energy can cause this ratio to approach the lower limit.

## Contribution

It explores the effects of dark energy on the shear viscosity to entropy density ratio in accretion flows, a novel context for testing the universal bound.

## Key findings

- Ratio approaches the lower bound in certain accretion flows with strong magnetic fields.
- Dark energy's negative pressure reduces shear viscosity significantly.
- High entropy density of dark energy influences the viscosity-to-entropy ratio.

## Abstract

The universal lower bound of the ratio of shear viscosity to entropy density is suggested by the string theory and gauge duality for any matter. We examined the ratio of shear viscosity to entropy density for viscous accretion flow towards a central gravitating object in the presence of dark energy. The ratio appears close to the universal lower bound for certain optically thin, hot accretion flows as they are embedded by strong magnetic field. Dark energy is a kind of exotic matter which has negative pressure. So dark energy creates repulsive force between the accreting particles, which indicates that shear viscosity of the flow becomes very low. Dark energy as accreting fluid has very high entropy density. The ratio should reach near to the lowest value for dark energy accretion. We wish to study what happens to the shear viscosity to entropy density ratio for viscous dark energy accretion flow.