Coincident General Relativity
  The metric-affine variational principle is applied to generate teleparallel
and symmetric teleparallel theories of gravity. From the latter is discovered
an exceptional class which is consistent with a vanishing affine connection.
Based on this remarkable property, this work proposes a simpler geometrical
formulation of General Relativity that is oblivious to the affine spacetime
structure, thus fundamentally depriving gravity of any inertial character. The
resulting theory is described by the Hilbert action purged from the boundary
term and is more robustly underpinned by the spin-2 field theory, where an
extra symmetry is now manifest, possibly related to the double copy structure
of the gravity amplitudes. This construction also provides a novel starting
point for modified gravity theories, and the paper presents new and simple
generalisations where analytical self-accelerating cosmological solutions arise
naturally in the early and late time universe.
