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Resolving the Hubble tension with emergent dark radiation in unitary gravity

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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.

This talk is part of the Cavendish Astrophysics Coffee talks series.

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