Quasi-dust ekpyrotic scenario in Loop Quantum Cosmology

Abstract

In the framework of Loop Quantum Cosmology, we study a cosmological bouncing model with two fields that reproduce the desired features of the primordial power spectra. The model combines the matter-bounce mechanism, that generates scale-invariant perturbations, with ekpyrotic contraction, that suppresses anisotropies leading to the bounce. The bounce that replaces the classical initial singularity is achieved thanks to the loop quantisation. The matter-bounce is enacted by a \textit{quasi-dust} scalar field, with a slightly-negative equation of state that accounts for a small positive cosmological constant, that generates a red-tilt in the perturbations' power spectra. A second field, endowed with an ekpyrotic potential, is introduced to tame the growth of anisotropies throughout the bouncing phase. The equations of motion of the scalar perturbations are non-trivially coupled, leading to rich phenomenology that cannot be inferred simply from their single-field counterpart. We study the evolution of scalar and tensor perturbations and compare the results to current observations, showing the viability of this model as a base for further investigations.