Conflict between some higher-order curvature invariant terms

A viable quantum theory does not allow curvature invariant terms of different higher orders to be accommodated in the gravitational action. We show that there is indeed a conflict between the curvature squared and Gauss-Bonnet squared terms from the point of view of hermiticity. This means one should choose either, in addition to the Einstein-Hilbert term, but never the two together. We explore early cosmic evolution with Gauss-Bonnet squared term. (C) 2021 The Author(s). Published by Elsevier B.V.

Automated summary

A viable quantum theory prohibits the inclusion of curvature invariant terms of different higher orders in the gravitational action. The study demonstrates a conflict between curvature squared and Gauss-Bonnet squared terms in terms of hermiticity, suggesting that one should choose either of them, but not both, in addition to the Einstein-Hilbert term. The early cosmic evolution is explored with the Gauss-Bonnet squared term included.