Speaker
Description
Pseudo-scalar axions are ubiquitous in high-energy theory, and so are their scalar partners, here called ‟dilatons”, that dynamicalise the corresponding gauge couplings. In this talk, I will discuss the cosmology of dilatons and axions, focussing on the impact of dilaton phase transitions. First, I will show how cosmological dilaton phase transitions can lead to the trapping and compression of axions into ‟axion relic pockets”: regions of false vacuum stabilised from collapse by the pressure of the kinematically trapped, hot axion gas. Axion relic pockets are naturally long-lived and could comprise all dark matter. Their sizes range from point-like to brick-sized, and their masses from intermediate particle-physics scales to asteroid-like. This new dark matter theory is economical: the macroscopic properties of the pockets depend only on a single parameter (the phase transition temperature). I will describe the formation, evolution and present-day properties of axion relic pockets, and outline how their phenomenology is distinct from existing dark matter paradigms. I will briefly outline how laboratory experiments and astronomical observations can be used to probe the theory. Second, I will briefly discuss how a dilaton phase transition involving the strong coupling constant of the Standard Model can make the QCD phase transition first-order, and lead to an intriguing gravitational wave signal in the nano-Hertz frequency range.
