Cosmological dynamics with propagating Lorentz connection modes of spin zero

TL;DR

This paper explores the cosmological implications of propagating spin-zero modes in Poincare gauge gravity, demonstrating how these modes influence universe acceleration and oscillations, with a focus on both spin-0+ and spin-0- modes.

Contribution

It extends previous work by including the spin-0- mode in the cosmological model, deriving the dynamic equations, and analyzing the late-time behavior of the universe.

Findings

Spin-0+ mode can cause accelerated expansion.

Spin-0- mode introduces oscillatory behavior in cosmic acceleration.

Dynamic modes decouple at late times, simplifying analysis.

Abstract

The Poincare gauge theory of gravity has a Lorentz connection with both torsion and curvature. For this theory two good propagating connection modes, carrying spin-$0^+$ and spin-$0^-$, have been found. The possible effects of the spin-$0^+$ mode in cosmology were investigated in a previous work by our group; there it was found that the $0^+$ mode could account for the presently accelerating universe. Here, we extend the analysis to also include the spin-$0^-$ mode. The resulting cosmological model has three degrees of freedom. We present both the Lagrangian and Hamiltonian form of the dynamic equations for this model, find the late-time normal modes, and present some numerical evolution cases. In the late time asymptotic regime the two dynamic modes decouple, and the acceleration of the Universe oscillates due to the spin-$0^+$ mode.