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Sachs equations and plane waves, I: Rosen universes
Jonathan Holland, George Sparling
https://arxiv.org/abs/2402.07036 https://arxiv.…

Sachs equations and plane waves, I: Rosen universes
This article, the first in a series, analyzes the general theory of plane wave spacetimes. Following Dmitri Aleekseevsky, these are defined as spacetimes admitting a group of dilations leaving invariant a smooth curve. If this curve is specified as part of the structure, the spacetime is termed a Penrose limit, whose theory was developed first by Roger Penrose. The main result is that every plane wave is a Rosen universe, a generalization of the smooth metrics of Albert Einstein and Nathan Rose…

This https://arxiv.org/abs/2310.03076 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_hept…

Boundary signature of singularity in the presence of a shock wave
Matter falling into a Schwarzschild-AdS black hole from the left causes increased focussing of ingoing geodesics from the right, and, as a consequence, they reach the singularity sooner. In a standard Penrose diagram, the singularity "bends down". We show how to detect this feature of the singularity holographically, using a boundary two-point function. We model the matter with a shock wave, and show that this bending down of the singularity can be read off from a novel analytic continuation of…