Cosmology

TL;DR

This paper reviews key issues in cosmology, including dark matter, baryon asymmetry, and early universe scenarios, emphasizing observational tests and the potential of future measurements to distinguish models.

Contribution

It provides a comprehensive overview of cosmological problems, hypotheses, and observational strategies, highlighting the importance of future data in understanding the early universe.

Findings

Weakly interacting massive particles and axions as cold dark matter candidates

Electroweak baryogenesis remains a viable explanation for baryon asymmetry

Inflation is the leading theory for the origin of primordial density perturbations

Abstract

Cosmology and particle physics are deeply interrelated. Among the common problems are dark energy, dark matter and baryon asymmetry of the Universe. We discuss these problems in general terms, and concentrate on several particular hypotheses. On the dark matter side, we consider weakly interacting massive particles and axions/axion-like particles as cold dark matter, sterile neutrinos and gravitinos as warm dark matter. On the baryon asymmetry side, we discuss electroweak baryogenesis as a still-viable mechanism. We briefly describe diverse experimental and observational approaches towards checking these hypotheses. We then turn to the earliest cosmology. We give arguments showing that the hot stage was preceded by another epoch at which density perturbations and possibly primordial gravity waves were generated. The best guess here is inflation, which is consistent with everything we know of density perturbations, but there are alternative scenarios. Future measurements of the properties of density perturbations and possible discovery of primordial gravity waves have strong potential in this regard.