Consistent inflationary cosmology from quadratic gravity with dynamical torsion

Abstract

The idea of gauge theories of gravity predicts that there should exist not only the massless graviton but also massive particles carrying the gravitational force. We study the cosmology in a quadratic gravity with dynamical torsion where gravity may be interpreted as a gauge force associated with the Poincaré group. In addition to the massless spin-2 graviton, the model contains four non-ghost massive particle species: a couple of spin-0, a spin-1 and a spin-2. Supposing the restoration of the local Weyl invariance in the UV limit and the parity invariance, we find the most general minisuperspace action describing a homogeneous and isotropic universe with a flat spatial geometry. We then transform the minisuperspace action to a quasi-Einstein frame in which the field space is a hyperboloid and the field potential is a combination of those of a Starobinsky-like inflation and a natural inflation. Remarkably, thanks to the multi-field dynamics, the Starobinsky-like inflationary trajectory can be realized even if the initial condition is away from the top of the Starobinsky-like potential. We also study linear tensor perturbations and find qualitatively different features than the Starobinsky inflation, spontaneous parity violation and mixing of the massless and massive spin-2 modes, which might reveal the underlying nature of gravity through inflationary observables.

arXiv comment35 pages, 5 figures, published version

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• Coupling Metric-Affine Gravity to a Higgs-Like Scalar Field
• Addressing $H_0$ tension with emergent dark radiation in unitary gravity
• Searching for Cosmological Collider in the Planck CMB Data
• Coupling Metric-Affine Gravity to the Standard Model and Dark Matter Fermions
• New black hole solutions with a dynamical traceless nonmetricity tensor in Metric-Affine Gravity
• Cosmological Perturbation Theory in Metric-Affine Gravity
• Plebański-Demiański solutions with dynamical torsion and nonmetricity fields
• Violation of slow-roll in non-minimal inflation
• Inflation in the general Poincaré gauge cosmology
• Non-linearly ghost-free higher curvature gravity
• Algebraic classification of the gravitational field in Weyl-Cartan space-times
• Radiative corrections to the $R$ and $R^2$ invariants from torsion fluctuations on maximally symmetric spaces
• Algebraic classification of the gravitational field in general metric-affine geometries