# Holographic Studies of The Generic Massless Cubic Gravities

## TL;DR

This paper explores massless cubic gravity theories in 4 and 5 dimensions, constructing approximate black hole solutions, establishing holographic parameters, and analyzing their implications for R'enyi entropy and hydrodynamics.

## Contribution

It introduces a broad class of massless cubic gravities beyond known models, derives approximate black hole solutions, and connects these to holographic quantities and physical properties.

## Key findings

- Black hole solutions exist perturbatively in these theories.
- Holographic parameters like $a$, $C_T$, $t_2$, and $t_4$ are computed.
- Deviations from the KSS bound are controlled by specific charge differences.

## Abstract

We consider the generic massless cubic gravities coupled to a negative bare cosmological constant mainly in $D=5$ and $D=4$ dimensions, which are Einstein gravity extended with cubic curvature invariants where the linearized excited spectrum around the AdS background contains no massive modes. The generic massless cubic gravities are more general than Myers quasi-topological gravity in $D=5$ and Einsteinian cubic gravity in $D=4$. It turns out that the massless cubic gravities admit the black holes at least in a perturbative sense with the coupling constants of the cubic terms becoming infinitesimal. The first order approximate black hole solutions with arbitrary boundary topology $k$ are presented, and in addition, the second order approximate planar black holes are exhibited as well. We then establish the holographic dictionary for such theories by presenting $a$-charge, $C_T$-charge and energy flux parameters $t_2$ and $t_4$. By perturbatively discussing the holographic R\'enyi entropy, we find $a$, $C_T$ and $t_4$ can somehow determine the R\'enyi entropy with the limit $q\rightarrow 1$, $q\rightarrow 0$ and $q\rightarrow \infty$ up to the first order, where $q$ is the order of the R\'enyi entropy. For holographic hydrodynamics, we discuss the shear-viscosity-entropy-ratio and find that the patterns deviating from the KSS bound $1/(4\pi)$ can somehow be controlled by $((c-a)/c,t_4)$ up to the first order in $D=5$, and $((\mathcal{C}_T-\tilde{a})/\mathcal{C}_T,t_4)$ up to the second order in $D=4$, where $\mathcal{C}_T$ and $\tilde{a}$ differ from $C_T$-charge and $a$-charge by inessential overall constants.