Ghostfree quadratic curvature theories with massive spin-2 and spin-0 particles

Understand

We consider generic derivative corrections to the Einstein gravity and find new classes of theories without ghost around the Minkowski background by means of an extension of the spacetime geometry.

• We assume the Riemann-Cartan geometry, i.e.
• a geometry with a non-vanishing torsion, and consider all possible terms in the Lagrangian up to scaling dimension four.
• We first clarify the number, spins, and parities of all particle species around the Minkowski background and find that some of those particle species are ghosts for generic choices of parameters.