Evidence for anisotropy of cosmic acceleration

Abstract

Observations reveal a "bulk flow" in the local Universe which is faster and extends to much larger scales than are expected around a typical observer in the standard ΛCDM cosmology. This is expected to result in a scale-dependent dipolar modulation of the acceleration of the expansion rate inferred from observations of objects within the bulk flow. From a maximum-likelihood analysis of the Joint Light-curve Analysis catalogue of Type Ia supernovae, we find that the deceleration parameter, in addition to a small monopole, indeed has a much bigger dipole component aligned with the cosmic microwave background dipole, which falls exponentially with redshift z: q 0 = q m + q d .n exp(−z/S ). The best fit to data yields q d = −8.03 and S = 0.0262 (⇒ d ∼ 100 Mpc), rejecting isotropy (q d = 0) with 3.9σ statistical significance, while q m = −0.157 and consistent with no acceleration (q m = 0) at 1.4σ. Thus the cosmic acceleration deduced from supernovae may be an artefact of our being non-Copernican observers, rather than evidence for a dominant component of "dark energy" in the Universe. Key words. cosmology: observations -dark energy -large-scale structure of UniverseArticle published by EDP Sciences L13, page 1 of 6 A&A 631, L13 (2019)

Evidence for cosmic acceleration with next-generation surveys: a model-independent approach

“…Given the still unknown nature of the current accelerated expansion, it is essential to quantify how well we can detect this phenomenon, since it could rule out the standard model, and even the possibility of the existence of the dark energy paradigm as a whole. Within the context of the standard model, cosmological observations show that the Universe is currently accelerating at roughly 5σ level (Shapiro & Turner 2006;Ishida et al 2008;Giostri et al 2012;Vargas dos Santos et al 2016;Rubin & Hayden 2016;Harisadu et al 2017;Tutusaus et al 2017;Lin et al 2018;Rubin & Heitlauf 2019), E-mail: Carlos.Bengaly@unige.ch albeit this result was recently disputed using the Hubble diagram of Type ia Supernovae (Nielsen et al 2016;Ringermacher & Mead 2016;Dam et al 2017;Colin et al 2019a;Rameez 2019;Colin et al 2019b) and quasars (Lusso et al 2019;Yang et al 2019;Velten & Gomes 2019). Other works looked at model-independent probes of cosmic acceleration, thus independent of dark energy, and even General Relativity assumptions, such as kinematic analyses (Rapetti et al 2007;Cunha & Lima 2008;Carvalho et al 2011;Lu et al 2011;Nair et al 2012;Muthukrishna & Parkinson 2016;Jesus et al 2018;Heneka 2018), besides non-parametric approaches (Mortsell & Clarkson 2009;Velten et al 2018;Harisadu et al 2018;Tutusaus et al 2019;Gómez-Valent 2019;Jesus et al 2019;Arjona & Nesseris al.…”

Challenging matter creation models in the phantom divide

“…For type Ia supernova we make use of the full Pantheon sample [23] incorporating the heliocentric redshift, correcting in this way the issue previously mentioned about peculiar velocities at high redshift [24]. The Hubble parameter as a function of redshift H(z) data is obtained by cosmic chronometers and taken from the compilation made in [25].…”

No single unification theory of everything

“…One important prediction from this inflation model is that the space dimensions undergo a double-inflation process and hence can present a signature of a dipole mode. This might explain the recent discovery of a large dipole component of cosmic acceleration in a reanalysis of type Ia supernova data by Colin et al [19]. The new gauge symmetry provides bosons with 96 degrees of freedom in each sector and the corresponding gauge supersymmetry of SMM 4 asks for new Dirac fermion particles (massless quarks and leptons) with the same 96 degrees of freedom in each sector [6,7].…”