Dear Colleagues,

Four major epochs are attributed to the history of the universe, with four outstanding problems associated with each one: inflation (issues related to initial conditions); radiation domination (baryogenesis); matter domination (the nature of dark matter); and late-time acceleration (the nature of the exotic matter/gravity modifications that cause acceleration). In this Special issue of Galaxies, the topic of baryogengesis will be the prime focus, and the study of formation dynamics primordial black holes (PBHs) and their effect on baryon-asymmetry generation will be reviewed extensively.

PBHs are generic objects produced in the early universe, which play a key role in understanding the nature of the nascent Universe as they may be the only probes to understand the end stage of the inflationary dynamics. Since they are formed at a very early stage, they are non-baryonic and are excellent candidates for Dark Matter. Even if PBHs do not comprise the total DM density, they undergo evaporation through the Hawking radiation mechanism; thus, the products of such processes could give rise to a fraction of the DM energy density. In a nutshell, studying the formation of PBHs and the associated dynamics could unravel many details about the early Universe.

As for baryon asymmetry, it is worth mentioning that one of the major successes of the hot big bang model is attributed to the synthesis of light elements in the early universe, dubbed nucleosynthesis, which requires baryon asymmetry as an input. Thus, the constraints from BBN on the dynamics of baryogenesis will be studied in detail.

It is intriguing to explore the connection between PBHs and baryon asymmetry in the universe. Interestingly, PBHs can efficiently generate GUT Higgs or gauge bosons through Hawking evaporation. Their evaporation following electro-weak phase transition can avoid the sphaleron washout problem otherwise encountered in GUT models based on SU(5).

Major efforts in terms of both high-energy physics and modern cosmology are required to address the problem of baryogenesis and its underlying connection to the evaporation mechanism of PBHs. Needless to say, this is an active research endeavor at the interface of the two fields.

This proposed Special Issue of Galaxies will focus on the dynamics of generation of PBHs and their prospect as a dark matter candidate. It will emphasize the dynamics behind baryogenesis and finally, the effort to discern the effect of PBHs evaporation on these baryon-asymmetry-generating processes.

Prof. Dr. Mohammad Sami
Dr. Mayukh Raj Gangopadhyay
Guest Editors

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