On the classification of consistent boundary conditions for $f(R)$-Gravity

Abstract

Using a completely covariant approach, we discuss the role of boundary conditions (BCs) and the corresponding Gibbons--Hawking--York (GHY) terms in $f(R)$-gravity in arbitrary dimensions. We show that $f(R)$-gravity, as a higher derivative theory, is not described by a degenerate Lagrangian, in its original form. Hence, without introducing additional variables, one can not obtain consistent BCs, even by adding the GHY terms (except for $f(R)=R$). However, following the Ostrogradsky approach, we can introduce a scalar field in the framework of Brans-Dicke formalism to the system to have consistent BCs by considering appropriate GHY terms. In addition to the Dirichlet BC, the GHY terms for both Neumann and two types of mixed BCs are derived. We show the remarkable result that the $f(R)$-gravity is itself compatible with one type of mixed BCs, in $D$ dimension, i.e. it doesn't require any GHY term. For each BC, we rewrite the GHY term in terms of Arnowit-Deser-Misner (ADM) variables.

21 pages

References in corpus (3)

• Holography of Gravitational Action Functionals
• An Alternate Path Integral for Quantum Gravity
• Einstein-Gauss-Bonnet theory of gravity: The Gauss-Bonnet-Katz boundary term

Cited by in corpus (5)

• Dynamic properties of cyclic cosmologies
• Classical Holographic Relations and Alternative Boundary Conditions for Lovelock Gravity
• On the well-posed variational principle in degenerate point particle systems using embeddings of the symplectic manifold
• Black Hole Entropy and Boundary Conditions
• Renormalization of the Einstein-Hilbert action