Non-parametric reconstruction of an inflaton potential from Einstein-Cartan-Sciama-Kibble gravity with particle production

TL;DR

This paper demonstrates that quantum particle production in Einstein-Cartan-Sciama-Kibble gravity can drive cosmic inflation, reconstructing a scalar potential consistent with observations without requiring a fundamental inflaton field.

Contribution

It introduces a non-parametric method to reconstruct the inflaton potential from a torsion-based gravity model, linking quantum particle production to inflationary dynamics.

Findings

Achieves exponential expansion with over 60 e-folds near the Big Bounce.

Reconstructed potential yields inflationary parameters consistent with Planck 2015 data.

Provides a scalar field potential derived from torsion and particle production effects.

Abstract

The coupling between spin and torsion in the Einstein-Cartan-Sciama-Kibble theory of gravity generates gravitational repulsion at very high densities, which prevents a singularity in a black hole and may create there a new universe. We show that quantum particle production in such a universe near the last bounce, which represents the Big Bang gives the dynamics that solves the horizon, flatness, and homogeneity problems in cosmology. For a particular range of the particle production coefficient, we obtain a nearly constant Hubble parameter that gives an exponential expansion of the universe with more than 60 $e$-folds, which lasts about $\sim 10^{-42}$ s. This scenario can thus explain cosmic inflation without requiring a fundamental scalar field and reheating. From the obtained time dependence of the scale factor, we follow the prescription of Ellis and Madsen to reconstruct in a non-parametric way a scalar field potential which gives the same dynamics of the early universe. This potential gives the slow-roll parameters of cosmic inflation, from which we calculate the tensor-to-scalar ratio, the scalar spectral index of density perturbations, and its running as functions of the production coefficient. We find that these quantities do not significantly depend on the scale factor at the Big Bounce. Our predictions for these quantities are consistent with the Planck 2015 observations.