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

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.
Comment: LaTeX, 35 pages, 3 figures, as published in J. High Energ. Phys. 2020, 90 (2020)