Mimetic-Metric-Torsion with induced Axial mode and Phantom barrier crossing

TL;DR

This paper extends mimetic-metric-torsion gravity to include axial modes and demonstrates the possibility of super-acceleration and phantom barrier crossing in cosmological evolution, consistent with near-$ ext{Λ}$CDM profiles.

Contribution

It introduces a coupling of the mimetic scalar field to the Holst extension, allowing geometric manifestation of torsion modes and cosmological implications like super-acceleration.

Findings

Super-accelerating universe regime is feasible.

Smooth crossing of the phantom barrier at low red-shift.

Torsion parameters evolve consistent with observational data.

Abstract

We extend the basic formalism of mimetic-metric-torsion gravity theory, in a way that the mimetic scalar field can manifest itself geometrically as the source of not only the trace mode of torsion, but also its axial (or, pseudo-trace) mode. Specifically, we consider the mimetic field to be (i) coupled explicitly to the well-known Holst extension of the Riemann-Cartan action, and (ii) identified with the square of the associated Barbero-Immirzi field, which is presumed to be a pseudo-scalar. The conformal symmetry originally prevalent in the theory would still hold, as the associated Cartan transformations do not affect the torsion pseudo-trace, and hence the Holst term. Demanding the theory to preserve the spatial parity symmetry as well, we focus on a geometric unification of the cosmological dark sector, and show that a super-accelerating regime in the course of evolution of the universe is always feasible. From the observational perspective, assuming the cosmological evolution profile to be very close to that for $\L$CDM, we further show that there could be a smooth crossing of the so-called phantom barrier at a low red-shift, however for a very restricted parametric domain. The extent of the super-acceleration have subsequently been ascertained by examining the evolution of the relevant torsion parameters.