Quartet-metric gravity, scalar-graviton dark substance and vacuum energy screening: extending GR vs. its WTDiff alternative

TL;DR

This paper explores an extension of general relativity via quartet-metric gravity, introducing a scalar graviton that can partially screen vacuum energy, and compares it with the Weyl transverse alternative, highlighting their differences and implications for dark energy.

Contribution

It develops a consistent framework for scalar-graviton extensions of GR and WTDiff gravity, analyzing their field equations and implications for vacuum energy screening.

Findings

Scalar graviton extends tensor gravity in quartet-metric framework.

Field equations differ between GR and WTDiff extensions.

Partial vacuum energy screening via scalar-graviton dark substance.

Abstract

In the frameworks of the effective field theory of metric supplemented by some distinct dynamical coordinates parametrized, in turn, by a scalar quartet -- the so-called quartet-metric gravity -- the extension of tensor gravity through a massive scalar graviton in addition to the massless tensor one is consistently exposed. The field equations for the two realizations of such an extension originating from the classically equivalent prototype theories - General Relativity (GR) and its Weyl transverse (WTDiff) alternative - are derived and argued to be, generally, non-equivalent, with the pure-gravity case manifesting this explicitly in detail. A splitting of the cosmological constant onto the gravitating and non-gravitating parts, with a partial screening of the vacuum energy through an emergent scalar-graviton dark substance, is considered. A prior importance of treating the WTDiff gravity as a prototype one on par with GR, when looking for a putative next-to-GR extended theory of gravity with a scalar-graviton dark substance, is stressed.