A $\Lambda$CDM Extension Explaining the Hubble Tension and the Spatial Curvature $\Omega_{k,0} = -0.012 \pm 0.010$ Measured by the Final PR4 of the Planck Mission

Autor(en)

Horst Foidl, Tanja Rindler-Daller

Abstrakt

The measurements of the CMB have determined the cosmological parameters

with high accuracy, and the observation of the flatness of space have

contributed to the status of the concordance $\Lambda$CDM model.

However, the cosmological constant $\Lambda$, necessary to close the

model to critical density, remains an open conundrum. We explore the

observed late-time accelerated expansion of the Universe, where we

consider that the Friedmann equation describes the expansion history of

FLRW universes in the local reference frame of freely falling comoving

observers, which perceive flat, homogeneous and isotropic space in their

local inertial system, where, as a consequence of the equivalence

principle, special relativity applies. We use this fact to propose an

extension to $\Lambda$CDM, incorporating the initial conditions of the

background universe, comprising the initial energy densities as well as

the initial post big bang expansion rate. The observed late-time

accelerated expansion is then attributed to a kinematic effect akin to a

dark energy component. Choosing the same $\Omega_{m,0} \simeq 0.3$ as

$\Lambda$CDM, its equation of state $w_{de} \simeq -0.8$. Furthermore,

we include the impact on the expansion history caused by the cosmic web

of the late Universe, once voids dominate its volume, and find that the

initially constant $w_{de}$ becomes time-dependent, evolving to a value

of $w_{de} \simeq -0.9$ at the present. While this impact by voids is

minor, it is sufficient to provide a solution to the Hubble tension

problem. We use CLASS to calculate the expansion history and power

spectra of our extension and compare our results to concordance

$\Lambda$CDM and to observations. We find that our model agrees well

with current data, in particular with the final data release PR4 of the

Planck mission, where it explains the reported spatial curvature of

$\Omega_{k,0} = - 0.012 \pm 0.010$.

Organisation(en)

Institut für Astrophysik

Externe Organisation(en)

Universität Wien

Journal

Astronomy & Astrophysics

ISSN

0004-6361

Publikationsdatum

12-2024

Peer-reviewed

Ja

ÖFOS 2012

103003 Astronomie, 103004 Astrophysik

Schlagwörter

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/156a5acc-56aa-4ea1-b584-b8ae6cacf556