Two-field disformal transformation and mimetic cosmology

Abstract

We extend the disformal transformation to models with two scalar fields and look at its singular limit. Solving the eigentensor equation for the Jacobian of the transformation of the metrics we find the two-field extension of the mimetic scenario in the singular conformal limit. At the background level the setup mimics the roles of dark matter cosmology. We decompose the perturbations into the adiabatic and entropy modes in which the adiabatic perturbation is tangential to the classical trajectory while the entropy mode is perpendicular to it. We show that the adiabatic mode is frozen while the entropy mode propagates with the sound speed equal to unity with no instabilities.