A Complete Classification of Higher Derivative Gravity in 3D and Criticality in 4D
arXiv:1109.4458 · doi:10.1088/0264-9381/29/1/015002
Abstract
We study the condition that the theory is unitary and stable in three-dimensional gravity with most general quadratic curvature, Lorentz-Chern-Simons and cosmological terms. We provide the complete classification of the unitary theories around flat Minkowski and (anti-)de Sitter spacetimes. The analysis is performed by examining the quadratic fluctuations around these classical vacua. We also discuss how to understand critical condition for four-dimensional theories at the Lagrangian level.
20 pages, v2: minor corrections, refs. added, v3: logic modified, v4: typos corrected