Null Boundary Terms for Gravitational Action

Krishna Mohan Parattu (ICN-UNAM)

RESUMEN: Three years back, we had proposed a null boundary term for the Einstein-Hilbert action, complementing the Gibbons-Hawking-York boundary term which is used on non-null boundaries. This proposal has found applications in diverse fields such as string theory, holography, causal set theory, analysis of gravitational degrees of freedom, etc. I will review the history of boundary terms in gravity, our proposal, subsequent work extending and refining our proposal and mention some applications. Finally, I will briefly describe our recent work deriving a null boundary term for Lovelock (Lanczos-Lovelock) gravity.