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Abstract:

Within the standard cosmology — and indeed even within most commonly studied modified cosmologies — the history of the universe effectively consists of a sequence of single-component epochs with only brief transition periods between them.  However, many extensions of the Standard Model predict the existence of towers of unstable states.  Such towers often lead to a form of “cosmological stasis” in the early universe wherein the relative cosmological abundances of different energy components remain unchanged over an extended period, even as the universe expands.  The emergence of stasis is not a consequence of fine-tuning in cosmologies of this sort; rather, stasis turns out to be a global attractor toward which the universe naturally evolves for a broad range of initial conditions.  In this talk, I shall review the general conditions under which stasis emerges in such scenarios and discuss particular realizations of this phenomenon, such as those involving towers of Kaluza-Klein states or populations of primordial black holes with an extended mass spectra.  I shall also examine some of the potential implications of a stasis epoch for the evolution of primordial density perturbations and the growth of structure and for the primordial gravitational-wave background.

Brooks Thomas, a professor at Lafayette College, works as a theoretical particle physicist and is primarily focused on identifying the nature and properties of the mysterious dark matter in our Universe.

The McDonald Institute seminar will be held in Stirling 501. A Zoom link is also available and shared via email by the organizers. Please reach out to admin@mcdonaldinstitute.ca for access.