Phys. Rev. D, 110, 064009 (2024)

Gravitational vacua in the Newman-Penrose formalism

PuJian Mao

Center for Joint Quantum Studies and Department of Physics, School of Science, Tianjin University, 135 Yaguan Road, Tianjin 300350, China.

* pjmao@tju.edu.cn

Abstract

In this paper, we derive the generic solution of the Newman-Penrose equations in the Newman-Unti gauge with vanishing curvature tensor. The obtained solutions are the vacua of the gravitational theory which are connected to the derivations in metric formalism from exponentiating the infinitesimal BMS generators in the BMS gauge in Compère and Long [J. High Energy Phys. 07 (2016) 137 and Classical Quantum Gravity 33, 195001 (2016)] by a radial transformation. The coordinate transformations in the Newman-Unti gauge connecting each vacuum are also obtained. We confirm that the supertranslation charge of the gravitational vacua with respect to global considerations vanishes exactly not only in the Einstein theory but also when including the Holst, Pontryagin, and Gauss-Bonnet terms which verifies that the gravitational vacua are not affected by those trivial or boundary terms.