A number of challenges to the standard Λ CDM model have been emerging during the past
few years as the accuracy of cosmological observations improves. In this review we discuss …

The simplest ΛCDM model provides a good fit to a large span of cosmological data but
harbors large areas of phenomenology and ignorance. With the improvement of the number …

Despite the remarkable success of the Λ Cold Dark Matter (Λ CDM) cosmological model, a
growing discrepancy has emerged (currently measured at the level of∼ 4− 6 σ) between the …

We review the current status of Early Dark Energy (EDE) models proposed to resolve the
“Hubble tension”, the discrepancy between “direct” measurements of the current expansion …

The Λ CDM model provides a good fit to most astronomical observations but harbors large
areas of phenomenology and ignorance. With the improvements in the precision and …

Since the expansion of the universe was first established by Edwin Hubble and Georges
Lemaître about a century ago, the Hubble constant H_0 H 0 which measures its rate has …

The strong discrepancy between local and early-time (inverse distance ladder) estimates of
the Hubble constant H 0 could be pointing towards new physics beyond the concordance Λ …

We explore whether nonstandard dark sector physics might be required to solve the existing
cosmological tensions. The properties we consider in combination are (a) an interaction …

Emerging high-redshift cosmological probes, in particular quasars (QSOs), show a
preference for larger matter densities, Ω m≈ 1, within the flat Λ CDM framework. Here, using …

Gravitational waves can provide an accurate measurement of the luminosity distance to the
source but cannot provide the source redshift unless the degeneracy between mass and …