Holography with Null Boundaries

One of the key issues in holography is going beyond $\mathrm{AdS}$ and defining quantum gravity in spacetimes with a null boundary. Recent examples of this type involve linear dilaton asymptotics and are related to the $T \overline{T}$ deformation. We present a holographic correspondence derived from string theory, which is an example of a kind of celestial holography. The holographic definition is a spacetime non-commutative open string theory supported on D1-D5 branes together with fundamental strings. The gravity solutions interpolate between $\mathrm{AdS}_3$ metrics and six-dimensional metrics. Radiation can escape to null infinity, which makes both the encoding of quantum information in the boundary and the dynamics of black holes quite different from $\mathrm{AdS}$ spacetimes.