Dear Colleagues,

Observational cosmology has experienced impressive advances in the last 25 years, and it will continue improving in this decade thanks to the launch of the next generation of satellites, new ground-based CMB experiments, and the opening of new windows to the universe that will allow us to exploit the cosmological information encoded in gravitational waves, HI intensity maps, etc. Although the ΛCDM model has been able to explain a large variety of cosmological observations, ranging from the Hubble diagram of high-redshift supernovae of type Ia to the very precise CMB anisotropy maps measured by Planck, it is not free of tensions and there are still many open (and very fundamental) questions concerning some of the building blocks of the model. For instance,

→ How can we explain, using theory, the tiny value measured of the energy density associated with the cosmological constant?

→ Is dark energy rigid or is it a dynamic entity?

→ Is general relativity the gravitational theory governing the cosmological evolution of the universe, or is it modified at very large scales?

→ What is the nature of dark matter?

→ Are there interactions between the components of the dark sector?

Some of these questions may be intimately related to the cosmological tensions that affect the concordance model, e.g., the $H_0$ and $\sigma_8$ tensions. The latter are very hot topics of current research. If they are not caused by any unaccounted systematic error in the data, they might be pointing to the need of some sort of new physics in the gravitational and/or the matter sectors.

Current cosmological observations allow us to also place constraints on some properties of elementary particles, e.g., the total sum of neutrino masses, and to extract, in some cases, quite model-independent information about the geometry (background expansion and clustering) of the universe.

This Special Issue is open to contributions from theorists,  observationalists, and researchers bridging the gap between theory and observations. It aims to gather a series of works tackling the questions posed above, and studies about the impact of current and future cosmological observations on our understanding of the universe.

Dr. Adrià Gómez-Valent
Guest Editor

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• dark energy
• modified gravity
• cosmological constant problem
• massive neutrinos
• cosmological tensions
• large-scale structure
• Hubble parameter $H_0$
• model-independent reconstruction of cosmological functions
• cosmological forecasts