Null boundary terms for Lanczos-Lovelock gravity

Understand

We derive boundary terms appropriate for the general Lanczos-Lovelock action on a null boundary, when Dirichlet boundary conditions are imposed.

• We believe that these boundary terms have been derived for the first time in the literature.
• In this derivation, we rely only on the structure of the boundary variation of the action for Lanczos-Lovelock gravity.
• We also provide the null boundary term for Gauss-Bonnet gravity separately.