Speaker
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Abstract: In this talk, we perform a dynamical systems study of purely kinetic k-essence. Although the single-field models considered here have been studied in the past, a comprehensive study of the phase-space dynamics, incorporating stability conditions to ensure theoretical consistency, is lacking. Our results confirm rigorously and clearly that these models i) cannot explain in a unified way the dark matter and dark energy components of the cosmic fluid, and ii) are not adequate to explain the observed abundance of cosmic structure because of the inexistence of a saddle critical point mimicking a like dark matter period.
Based exclusively on the action and the derived equations of motion, we confirm these results analytically by showing that purely kinetic k-essence is incompatible with the prototype of dark-sector unification, namely the ΛCDM model, independent of the k-essence Lagrangian (this includes single-field and multi-field models). Our results place purely kinetic k-essence models in a difficult situation as viable candidates for the unification of dark matter and dark energy.