Wider research context

In the 1960s, Lévy-Leblond introduced the ultra-relativistic limit of the Poincare group where the speed of light is sent to zero, dubbed "Carrollian". Since his pioneering work, Carrollian physics has played a key role in numerous research directions, including fluid/gravity and holographic correspondences, asymptotically flat spacetimes at null infinity, and the related Bondi-van der Burgh-Metzner-Sachs symmetries, cosmology, and geometries of null hypersurfaces such as black hole horizons. Since many of these research directions are fairly recent, Carrollian physics has become a timely and rapidly evolving topic.

One defining aspect of Carrollian physics is the collapse of the lightcone, while the defining property of a black hole requires the notion of a lightcone so that an event horizon can be identified. From this geometric perspective, it seems that something like a Carrollian black hole might not exist. Nevertheless, several authors (including the PI and his research group) have found evidence in the past few years that black hole-like entities could exist in Carrollian gravity. These discoveries make it urgent to provide a clear and useful definition of Carrollian black holes, as well as to study their physical properties, such as their entropy.

Research questions

The main goal of the project is to define a meaningful notion of black holes in Carrollian theories of gravity and to study the consistency and applications of this notion. In particular, we aim to discover the Carrollian analog of the Bekenstein-Hawking entropy formula.

Methods

The theories considered initially will be two-dimensional Carrollian dilaton gravity models (introduced simultaneously by the PI with collaborators and by a competing group in 2020), where one has full analytic control over the theory and its classical solutions. After checking the consistency of our proposal, including thermodynamical properties such as the entropy and how it relates to Cardy-type of counting arguments, we intend to generalize and apply our definition of black holes to Carrollian gravity in more than two dimensions.

Level of originality

The proposed definition of Carrollian black holes was made for the first time by the PI at a workshop in Vienna in February 2022, so large parts of the project revolve around conceptually novel features, which have not received scrutiny yet. The entropy formula we are aiming for could play the same role for Carrollian black holes as the Bekenstein-Hawking formula did for ordinary black holes.

Primary researchers involved

PI, 1 postdoc (to be hired), 1 Ph.D. student (to be hired), international collaborators, and former research group members