Boundary Conditions and Quasilocal Energy in the Canonical Formulation of All 1+1 Models of Gravity

Within a first-order framework, we comprehensively examine the role played by boundary conditions in the canonical formulation of a completely general two-dimensional gravity model. Our analysis particularly elucidates the perennial themes of mass and energy. The gravity models for which our arguments are valid include theories with dynamical torsion and so-called generalized dilaton theories (GDTs). Our analysis of the canonical action principle (i) provides a rigorous correspondence between the most general first-order two-dimensional Einstein–Cartan model (ECM) and GDT and (ii) allows us to extract in a virtually simultaneous manner the “true degrees of freedom” for both ECMs and GDTs. For all such models, the existence of an absolutely conserved (in vacuo) quantityCis a generic feature, with (minus)Ccorresponding to the black-hole mass parameter in the important special cases of spherically symmetric four-dimensional general relativity and standard two-dimensional dilaton gravity. The massCalso includes (minimally coupled) matter into a “universal mass function.” We place particular emphasis on the (quite general) class of models within GDT possessing a Minkowski-like groundstate solution (allowing comparison betweenC and the Arnowitt–Deser–Misner mass for such models).