A gravitational realization of Courant--Hilbert deformations

Abstract

Courant--Hilbert (CH) deformations unify broad classes of solvable stress-tensor flows including $T\bar{T}$ and root-$T\bar{T}$. However, a gravitational action that systematically yields such general deformations has remained unknown. In this Letter, we construct a two-dimensional massive gravity theory whose on-shell action reproduces the complete CH deformation. The gravity sector is defined via an arbitrary function of the eigenvalue ratio $y$ of the relative zweibein. To bypass the technical difficulty of directly eliminating the auxiliary zweibein, we reformulate the matter sector using a $2\times 2$ spectral decomposition involving $y$ and a rank-one projector $K$. Sequentially solving the equations of motion---first for $K$ and subsequently for $y$---naturally maps the system onto the Russo-Townsend form of the CH flow. Our work extends Tolley's massive gravity formulation of $T\bar{T}$ flows to the CH landscape, providing a clear geometric mechanism for solvable stress-tensor flows.

arXiv comment6 pages; v2: references and comments added