Ghosts in pure and hybrid formalisms of gravity theories: a unified analysis

Understand

In the first order formalism of gravitational theories, the spacetime connection is considered as an independent variable to vary together with the metric.

• However, the metric still generates its Levi-Civita connection that turns out to determine the geodesics of matter.
• Recently, "hybrid" gravity theories have been introduced by constructing actions involving both the independent Palatini connection and the metric Levi-Civita connection.
• In this study a method is developed to analyse the field content of such theories, in particular to determine whether the propagating degrees of freedom are ghosts or tachyons.