Cosmological Stasis from Dynamical Scalars: Tracking Solutions and the Possibility of a Stasis-Induced Inflation
arxiv(2024)
Abstract
It has recently been realized that many theories of physics beyond the
Standard Model give rise to cosmological histories exhibiting extended epochs
of cosmological stasis. During such epochs, the abundances of different energy
components such as matter, radiation, and vacuum energy each remain fixed
despite cosmological expansion. In previous analyses of the stasis phenomenon,
these different energy components were modeled as fluids with fixed, unchanging
equations of state. In this paper, by contrast, we consider more realistic
systems involving dynamical scalars which pass through underdamping transitions
as the universe expands. Indeed, such systems might be highly relevant for BSM
scenarios involving higher-dimensional bulk moduli and inflatons. Remarkably,
we find that stasis emerges even in such situations, despite the appearance of
time-varying equations of state. Moreover, this stasis includes several new
features which might have important phenomenological implications and
applications. For example, in the presence of an additional "background" energy
component, we find that the scalars evolve into a "tracking" stasis in which
the stasis equation of state automatically tracks that of the background. This
phenomenon exists even if the background has only a small initial abundance. We
also discuss the intriguing possibility that our results might form the basis
of a new "Stasis Inflation" scenario in which no ad-hoc inflaton potential is
needed and in which there is no graceful-exit problem. Within such a scenario,
the number of e-folds of cosmological expansion produced is directly related to
the hierarchies between physical BSM mass scales. Moreover, non-zero matter and
radiation abundances can be sustained throughout the inflationary epoch.
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