Physics

Gravitation

Spacetime

Cosmological constant

Mathematics

Mathematical physics

Graviton

General relativity

Gauss–Bonnet theorem

Einstein

Singularity

Geometry

Gauss–Bonnet gravity

Theoretical physics

Massless particle

Quantum mechanics

Classical mechanics

Physical Review Letters

In this Letter we present a general covariant modified theory of gravity in D=4 spacetime dimensions which propagates only the massless graviton and bypasses Lovelock's theorem. The theory we present is formulated in D>4 dimensions and its action consists of the Einstein-Hilbert term with a cosmological constant, and the Gauss-Bonnet term multiplied by a factor 1/(D-4). The four-dimensional theory is defined as the limit D→4. In this singular limit the Gauss-Bonnet invariant gives rise to nontrivial contributions to gravitational dynamics, while preserving the number of graviton degrees of freedom and being free from Ostrogradsky instability. We report several appealing new predictions of this theory, including the corrections to the dispersion relation of cosmological tensor and scalar modes, singularity resolution for spherically symmetric solutions, and others.

Einstein-Gauss-Bonnet Gravity in Four-Dimensional Spacetime