Quasilocal conformal Killing horizons: Classical phase space and the first law

In realistic situations, black hole spacetimes do not admit a global timelike Killing vector field. However, it is possible to describe the horizon in a quasilocal setting by introducing the notion of a quasilocal boundary with certain properties which mimic the properties of a black hole inner boundary. Isolated horizons and Killing horizons are examples of such a kind. In this paper, we construct such a boundary of spacetime which is null and admits a conformal Killing vector field. Furthermore we construct the space of solutions (in general relativity) which admits such quasilocal conformal Killing boundaries. We also establish a form of the first law for these quasilocal horizons.