Quartic Horndeski, planar black holes, holographic aspects and universal bounds

TL;DR

This paper introduces new black hole solutions in a quartic Horndeski gravity model, examines their thermodynamics and holographic transport properties, and finds notable violations of universal bounds in heat conductivity and viscosity ratios.

Contribution

It presents novel planar black hole solutions with axionic hair in a shift-invariant quartic Horndeski model and analyzes their impact on holographic bounds.

Findings

Violation of heat conductivity-to-temperature bound depending on scale and coupling

Significant violation of the viscosity-to-entropy ratio bound

Black hole solutions exhibit unique thermodynamic and transport properties

Abstract

In this work, we consider a specific shift-invariant quartic Horndeski model, deriving new planar black hole solutions with axionic hair. We explore these solutions in terms of their horizon structure and their thermodynamic properties. We use the gauge/gravity dictionary to derive the DC transport coefficients of the holographic dual with the aim of investigating how the new deformation affects the universality of some renown bound proposals. Although most of them are found to hold true, we nevertheless find a highly interesting parametric violation of the heat conductivity-to-temperature lower bound which acquires a dependence on both the scale and the coupling. Finally, using a perturbative approach, a more brutal violation of the viscocity-to-entropy ratio is demonstrated.