The de Sitter spacetime as attractor solution in eighth-order gravity

From the Lagrangian R Square Operator Square Operator R one gets an eighth-order theory of gravitation. It has more promising properties than the previously discussed sixth-order ones. The de Sitter solution has the attractor property; we explicitly show how the modes decay. Further, exactly one power law and one pole-like solution exist. Adding the Einstein-Hilbert and other lower order terms with suitably chosen coefficients, we get a theory without tachyons, with the correct Newtonian limit and with cosmological solutions possessing more than one inflationary phase. (Whether double inflation is typical still remains open).