Mathematische Annalen.
Springer.
Том 379.
2021.
С. 1767-1805
We study the problem of the instability of inhomogeneous radiation universes in quadratic Lagrangian theories of gravity written as a system of evolution equations with constraints. We construct formal series expansions and show that the resulting solutions have a smaller number of arbitrary functions than that required in a general solution. These results continue to hold for more general polynomial extensions of general relativity. © 2021 World Scientific Publishing Company.