Dof(R)theories matter?

Traversable wormholes and time machines in nonminimally coupled curvature-matterf(R)theories

“…A relevant point is that there are various Lagrangian densities compatible with the equation of state of a perfect fluid [7]. Here we chose L M = −ρ(r) [8].…”

Impulsive gravitational waves of massless particles in extended theories of gravity

“…Because of the very small expected value of the coupling constant λ, this would be a small contribution; see Ref. [37] for a discussion of bounds on the values of λ.…”

Wormholes and Time-Machines in Nonminimally Coupled Matter-Curvature Theories of Gravity

“…NMC theories have striking properties such as the nonconservation of the energy momentum tensor, which leads to deviation from geodesic motion of test particles [7], putative deviations from hydrodynamic equilibrium of stars [8], and the breaking of the degeneracy of the Lagrangian densities, which in GR give rise to the energy-momentum tensor of perfect fluids [9].…”