Higgs inflation in Einstein-Cartan gravity

TL;DR

This paper explores Higgs-driven inflation within Einstein-Cartan gravity, revealing conditions under which inflation aligns with observations and predicting a wide range of tensor-to-scalar ratios, including potential detectability of gravitational waves.

Contribution

It introduces a novel Higgs inflation model in Einstein-Cartan gravity with additional coupling constants, unifies known models in certain limits, and analyzes quantum correction effects.

Findings

Inflation is viable and observationally consistent in this framework.

Tensor-to-scalar ratio can vary widely, including detectable levels.

Known Higgs inflation models are recovered in specific limits.

Abstract

We study inflation driven by the Higgs field in the Einstein-Cartan formulation of gravity. In this theory, the presence of the Holst and Nieh-Yan terms with the Higgs field non-minimally coupled to them leads to three additional coupling constants. For a broad range of parameters, we find that inflation is both possible and consistent with observations. In most cases, the spectral index is given by $n_s=1-2/N_\star$ (with $N_\star$ the number of e-foldings) whereas the tensor-to-scalar ratio $r$ can vary between about $10^{-10}$ and $1$. Thus, there are scenarios of Higgs inflation in the Einstein-Cartan framework for which the detection of gravitational waves from inflation is possible in the near future. In certain limits, the known models of Higgs inflation in the metric and Palatini formulations of gravity are reproduced. Finally, we discuss the robustness of inflationary dynamics against quantum corrections due to the scalar and fermion fields.