Tensions, Anomalies, and Challenges in the Standard Cosmological Model

Dear Colleagues,

Cosmology has evolved from a largely theoretical pursuit to a dynamic science driven by an explosion of modern data. The revolution began with observations of large angular fluctuations in the cosmic microwave background, the discovery of dark energy with Type Ia Supernovae data, and multi-messenger studies spanning a huge range of energies and the electromagnetic spectrum. New avenues have also been opened in the last two decades such as BAO, gravitational waves, and fast radio bursts.

Precision data create the opportunity to test the very foundations of cosmology. Subjecting the “standard model of cosmology” to scrutiny has revealed many discrepancies with expectations, as well as conflicts between cosmological parameters derived from different observations. Some prominent topics include CMB anomalies that suggest a breakdown of isotropy, suggestions of a possible preferred direction in Type Ia Supernova data, and radio observations of quasars. The so-called S8 tension refers to unresolved measures of the lumpiness of the universe. There are outstanding questions regarding the consistency of the Hubble parameter estimated by different methods, including early- and late-time probes. The big picture has always lacked “particle” candidates for dark matter and dark energy, while basic issues about the consistency of the LCDM cosmology with relic abundance and galaxy formation have not improved. There are many ways that current observations might be signals of new physics waiting to be discovered.

This Special Issue aims to highlight known and emerging discrepancies that are called “anomalies”, “tensions”, and “challenges” for the current cosmological model. The articles collected in this Special Issue are intended to be a repository presenting the state of the art in this direction for current and future researchers confronting cosmology with theory and observational data of all kinds. Both original articles and reviews are welcome.

Prof. Dr. John P. Ralston
Dr. Pavan Kumar Aluri
Guest Editors

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• standard cosmological model—anomalies, tensions, challenges
• cosmological principle
• Hubble tension
• S8 tension
• dark matter and dark energy
• early- and late-time probes