Weakly dynamic dark energy via metric-scalar couplings with torsion
  We study the dynamical aspects of dark energy in the context of a
non-minimally coupled scalar field with curvature and torsion. Whereas the
scalar field acts as the source of the trace mode of torsion, a suitable
constraint on the torsion pseudo-trace provides a mass term for the scalar
field in the effective action. In the equivalent scalar-tensor framework, we
find explicit cosmological solutions representing dark energy in both Einstein
and Jordan frames. We demand the dynamical evolution of the dark energy to be
weak enough, so that the present-day values of the cosmological parameters
could be estimated keeping them within the confidence limits set for the
standard $\L$CDM model from recent observations. For such estimates, we examine
the variations of the effective matter density and the dark energy equation of
state parameters over different redshift ranges. In spite of being weakly
dynamic, the dark energy component differs significantly from the cosmological
constant, both in characteristics and features, for e.g. it interacts with the
cosmological (dust) fluid in the Einstein frame, and crosses the phantom
barrier in the Jordan frame. We also obtain the upper bounds on the torsion
mode parameters and the lower bound on the effective Brans-Dicke parameter. The
latter turns out to be fairly large, and in agreement with the local gravity
constraints, which therefore come in support of our analysis.
