Virialisation-induced curvature as a physical explanation for dark energy

Abstract

The geometry of the dark energy and cold dark matter dominated cosmological model (ΛCDM) is commonly assumed to be given by a Friedmann-Lemaître-Robertson-Walker (FLRW) metric, i.e. it assumes homogeneity in the comoving spatial section. The homogeneity assumption fails most strongly at (i) small distance scales and (ii) recent epochs, implying that the FLRW approximation is most likely to fail at these scales. We use the virialisation fraction to quantify (i) and (ii), which approximately coincide with each other on the observational past light cone. For increasing time, the virialisation fraction increases above 10% at about the same redshift (∼ 1-3) at which Ω Λ grows above 10% (≈ 1.8). Thus, instead of non-zero Ω Λ , we propose an approximate, general-relativistic correction to the matter-dominated (Ω m = 1, Ω Λ = 0), homogeneous metric (Einstein-de Sitter, EdS). A low-redshift effective matter-density parameter of Ω eff m (0) = 0.26 ± 0.05 is inferred. Over redshifts 0 < z < 3, the distance modulus of the virialisation-corrected EdS model approximately matches the ΛCDM distance modulus. This rough approximation assumes "old physics" (general relativity), not "new physics". Thus, pending more detailed calculations, we strengthen the claim that "dark energy" should be considered as an artefact of emerging average curvature in the void-dominated Universe, via a novel approach that quantifies the relation between virialisation and average curvature evolution.1 Affiliation b: during visiting lectureship. 2 Affiliation b: during long-term visit.

Observational challenges for the standard FLRW model

“…that of Ref. 39 and the virialization approximation, 101 have an average curvature parameter which evolves from a small value to a strongly negative average effective curvature today. In Ref.…”

The background Friedmannian Hubble constant in relativistic inhomogeneous cosmology and the age of the Universe

“…pec_expan-bbl tions of emerging average negative curvature models, include, e.g., toy models of collapsing and expanding spheres (Räsänen 2006) or Lemaître-Tolman-Bondi (LTB) regions (Nambu & Tanimoto 2005;Kai et al 2007), a peak model (Räsänen 2008), a metric template model (Larena et al 2009;Chiesa et al 2014), bi-scale or more general multi-scale models (Wiegand & Buchert 2010;Buchert & Räsänen 2012), the Timescape model (Wiltshire 2009;Duley, Nazer, & Wiltshire 2013;Nazer & Wiltshire 2015), the virialisation approximation (Roukema, Ostrowski, & Buchert 2013), an effective viscous pressure approach , and Swiss cheese models that paste exact inhomogeneous solutions into holes in a homogeneous (FLRW) background (Bolejko & Célérier 2010; the Tardis model of Lavinto, Räsänen, & Szybka 2013). Updates to many of these models should benefit from an observationally justified estimate of H bg 1 .…”

“…[See also recent work on averaging of LTB (Sussman et al 2015;Chirinos Isidro et al 2016) and Szekeres models (Bolejko 2009); for evolving sign-of-curvature models, see e.g. Krasinski (1981Krasinski ( , 1982Krasinski ( , 1983Stichel (2016); for averaging using Cartan scalars, see Coley (2010); Kašpar & Svítek (2014 Roukema et al 2013), then, through Eqs. (7) and (8), presented below in Sect.…”

Observational challenges for the standard FLRW model

“…Both the models, as in the case of template metrics that match the supernovae type Ia distance-modulus-redshift relation, i.e., that of Ref. 39 and the virialisation approximation [101], have an average curvature parameter which evolves from a small value to a strongly negative average effective curvature today. In Ref.…”