2d theory for asymptotic dynamics of 4d (self-dual) Einstein gravity

In this paper, we present a simple chiral 2d theory living on a momentum space celestial sphere whose behaviour exactly produces various IR dynamics of recent resurged interests for 4d (selfdual) Einstein gravity in asymptotically flat spacetimes. We demonstrate how to use simple 2d CFT computations to reproduce 4d BMS algebra and $w_{1+\infty}$ algebra, deduce the form of both chiral and anti-chiral stress tensors and recover the necessity for dressing hard particles asymptotically with soft modes. We further discuss how possible extensions of this 2d theory incorporates further dynamical information of 4d Einstein gravity.