Mapping Poincar'{e} gauge cosmology to Horndeski theory for emergent dark energy. (arXiv:2006.03581v2 [gr-qc] UPDATED)
<a href="http://arxiv.org/find/gr-qc/1/au:+Barker_W/0/1/0/all/0/1">W. E. V. Barker</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Lasenby_A/0/1/0/all/0/1">A. N. Lasenby</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Hobson_M/0/1/0/all/0/1">M. P. Hobson</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Handley_W/0/1/0/all/0/1">W. J. Handley</a>
The ten-parameter, quadratic Poincar’e gauge theory of gravity is a
plausible alternative to general relativity. We show that the rich background
cosmology of the gauge theory is described by a non-canonical bi-scalar-tensor
theory in the Jordan frame: the `metrical analogue’. This provides a unified
framework for future investigation by the broader community. For many parameter
choices, the non-canonical term reduces to a Cuscuton field of the form
$smash{sqrt{|X^{phiphi}|}}$. The Einstein-Cartan-Kibble-Sciama theory maps
to a pure quadratic Cuscuton, whereas the teleparallel theory maps to the
Einstein-Hilbert Lagrangian. We apply the metrical analogue to novel unitary
and power-counting-renormalisable cases of Poincar’e gauge theory. These
theories support the concordance $Lambda$CDM background cosmology up to an
optional, effective dark radiation component, we explain this behaviour in
terms of a stalled Cuscuton. We also obtain two dark energy solutions from one
of these cases: accelerated expansion from a negative bare cosmological
constant whose magnitude is screened, and emergent dark energy to replace
vanishing bare cosmological constant in $Lambda$CDM.
The ten-parameter, quadratic Poincar’e gauge theory of gravity is a
plausible alternative to general relativity. We show that the rich background
cosmology of the gauge theory is described by a non-canonical bi-scalar-tensor
theory in the Jordan frame: the `metrical analogue’. This provides a unified
framework for future investigation by the broader community. For many parameter
choices, the non-canonical term reduces to a Cuscuton field of the form
$smash{sqrt{|X^{phiphi}|}}$. The Einstein-Cartan-Kibble-Sciama theory maps
to a pure quadratic Cuscuton, whereas the teleparallel theory maps to the
Einstein-Hilbert Lagrangian. We apply the metrical analogue to novel unitary
and power-counting-renormalisable cases of Poincar’e gauge theory. These
theories support the concordance $Lambda$CDM background cosmology up to an
optional, effective dark radiation component, we explain this behaviour in
terms of a stalled Cuscuton. We also obtain two dark energy solutions from one
of these cases: accelerated expansion from a negative bare cosmological
constant whose magnitude is screened, and emergent dark energy to replace
vanishing bare cosmological constant in $Lambda$CDM.
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