HEP Theory Journal Club

Perturbations for a unified model of the dark sector

Rodrigo Cuzinatto

Universidade Federal de Alfenas and McGill University

We shall build the cosmological perturbations to a unified dark fluid with sharp transition in the late-time universe. The model evolves from a CDM-like behavior to a quasi-Λ phase in which the equation of state parameter is w = -1 + ε, with ε < 1 a constant. We show that the power spectrum associated to this model exhibits a growing mode scaling with hyperbolic functions of the scale k and the conformal time. This mode is dangerous for causing unphysical instabilities in the over-densities. The growing mode can be eliminated if the redshift of transition between the CDM regime and the quasi-Λ phase is nearly zero.