Cosmic inflation in metric-affine gravity

Abstract: In the context of metric-affine gravity theories, where the metric and connection are independent, we examine actions involving quadratic terms in the Ricci scalar curvature and the Holst invariant. These actions are non-minimally coupled to a scalar field. We explore the behavior of the corresponding effective metric theory, which includes an extra dynamic pseudoscalar degree of freedom. Detailed analysis of inflationary predictions reveals compliance with recent observations across various parameters, potentially allowing a higher tensor-to-scalar ratio. The spectral index's direction of change varies based on parameter positioning.