Stealth solutions in mimetic gravity decouple from background dynamics on the lambda=0 branch but impose an infinite hierarchy of constraints on perturbations, rendering the screening limit non-uniform and pathological.
Two-field disformal transformation and mimetic cosmology
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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.
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UNVERDICTED 2representative citing papers
Higher-derivative extension of dark matter yields an imperfect fluid that matches pressureless dust on homogeneous backgrounds but generates acceleration and vorticity to avoid caustic singularities in inhomogeneous cosmologies.
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Fragility of stealth solutions in mimetic gravity
Stealth solutions in mimetic gravity decouple from background dynamics on the lambda=0 branch but impose an infinite hierarchy of constraints on perturbations, rendering the screening limit non-uniform and pathological.
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Imperfect dark matter with higher derivatives
Higher-derivative extension of dark matter yields an imperfect fluid that matches pressureless dust on homogeneous backgrounds but generates acceleration and vorticity to avoid caustic singularities in inhomogeneous cosmologies.