Black Hole Memory

Understand

The memory effect at null infinity, $\mathcal{I}^+$, can be defined in terms of the permanent relative displacement of test particles (at leading order in $1/r$) resulting from the passage of a burst of gravitational radiation.

• In $D=4$ spacetime dimensions, the memory effect can be characterized by the supertranslation relating the "good cuts" of $\mathcal{I}^+$ in the stationary eras at early and late retarded times.
• It also can be characterized in terms of charges and fluxes associated with supertranslations.
• Black hole event horizons are in many ways analogous to $\mathcal{I}^+$.