The Ashtekar-Hansen universal structure at spatial infinity is weakly pseudo-Carrollian

TL;DR

The work addresses how the universal structure at spatial infinity in asymptotically flat spacetimes can be viewed as a pseudo-Carrollian geometry, connecting this viewpoint to the kinematical-algebra program. It shows that Spi inherits a degenerate metric g_4 = π^* g_3 from the base dS_3, with symmetry group G ≃ SO(3,1) ⋉ T and a normal translation subgroup, and it situates Carrollian and conformal Carroll structures within this framework. By relating Ashtekar–Hansen’s asymptotic symmetries to Carrollian concepts, the paper clarifies how conservation laws and supercharges fit within the broader kinematic-algebra landscape, including AdSC-type contractions and their Carrollian limits. This provides a geometric bridge between spatial infinity structures, Carrollian physics, and the kinematical-spacetime program, with implications for understanding asymptotic symmetries and conserved quantities across null infinity.

Abstract

It is shown that Ashtekar and Hansens's Universal Structure at Spatial Infinity (SPI), which has recently be used to establish the conservation of supercharges from past null infity to future null infinity, is an example of a (pseudo-) Carollian structure. The relation to Kinematic Algebras is clarified.