Gravity Asymptotics with Topological Parameters

Understand

In four dimensional gravity theory, the Barbero-Immirzi parameter has a topological origin, and can be identified as the coefficient multiplying the Nieh-Yan topological density in the gravity Lagrangian, as proposed by Date et al.[1].

• Based on this fact, a first order action formulation for spacetimes with boundaries is introduced.
• The bulk Lagrangian, containing the Nieh-Yan density, needs to be supplemented with suitable boundary terms so that it leads to a well-defined variational principle.
• Within this general framework, we analyse spacetimes with and without a cosmological constant.