Kasner eons with matter: holographic excursions to the black hole singularity

Recent work has shown that introducing higher-curvature terms to the Einstein-Hilbert action causes the approach to a space-like singularity to unfold as a sequence of Kasner eons. Each eon is dominated by emergent physics at an energy scale controlled by higher-curvature terms of a given order, transitioning to higher-order eons as the singularity is approached. In this talk, I will first demonstrate how the presence of matter dramatically modifies the physics of these eons compared to the vacuum case. I will illustrate this by considering a family of quasi-topological gravities of arbitrary order minimally coupled to a scalar field. Then, I will explain the imprints of these eons on holographic observables. Specifically, I will demonstrate that the behavior of the thermal a-function, two-point functions of heavy operators, and holographic complexity can capture distinct signatures of the eons, making them valuable tools for diagnosing stringy effects near black hole singularities.