Self-accelerating Universe in modified gravity with dynamical torsion

TL;DR

This paper explores a ghost-free modified gravity model with dynamical torsion that admits a self-accelerating universe solution, potentially explaining cosmic acceleration without a cosmological constant.

Contribution

It introduces a new class of gravity models with dynamical torsion that are free of instabilities and can produce self-acceleration.

Findings

Existence of ghost-free, stable solutions with dynamical torsion

Self-accelerating solutions without a cosmological constant

Small effective cosmological constant achieved through coupling hierarchy

Abstract

We consider a model belonging to the class of gravities with dynamical torsion. The model is free of ghosts and gradient instabilities about Minkowski and torsionless Einstein backgrounds. We find that at zero cosmological constant, the model admits a self-accelerating solution with non-Riemannian connection. Small value of the effective cosmological constant is obtained at the expense of the hierarchy between the dimensionless couplings.