Abstract

We propose a one-parameter extension to LCDM , expected to strongly affect cosmological tensions. An effective dark radiation component in the early universe redshifts away as hot dark matter, then quintessence, leaving a falsifiable cosmic torsion field in the current epoch. Our modified gravity is a new Poincare gauge theory, foremost among the 33 theories recently found algorithmically to be both power-counting renormalisable and free from ghosts and tachyons. To obtain it, we systematically chart the cosmologies of these new theories, as special cases of the most general parity-preserving, Ostrogradsky-stable theory with a Yang-Mills action. As well as the massless 2+ graviton, our theory may contain a massive 0- graviton. The flat Friedmann equations are emergent for any spatial curvature (k-screening), with tension-resolving freedom at the scale-invariant epoch that reliably attracts away to modern LCDM evolution. We close with upcoming Hamiltonian analysis, COSMOMC validation and solar system tests.