Abstract
We study the cosmology of bimetric theory with a composite matter coupling. We find two possible branches of background evolution. We investigate the question of stability of cosmological perturbations. For the tensor and vector perturbations, we derive conditions on the absence of ghost and gradient instabilities. For the scalar modes, we obtain conditions for avoiding ghost degrees. In the first branch, we find that one of the scalar modes becomes a ghost at the late stages of the evolution. Conversely, this problem can be avoided in the second branch. However, we also find that the constraint for the second branch prevents the doubly coupled matter fields from being the standard ingredients of cosmology. We thus conclude that a realistic and stable cosmological model requires additional minimally coupled matter fields.
Highlights
Ionization energy and electron affinity are fundamental energy parameters that characterize the property of materials
The ionization energy is defined as the minimum energy required to remove an electron out of a neutral atom or molecule in its ground state, while the electron affinity is the energy released when an additional electron is attached to a neutral atom or molecule
The ionization energy and electron affinity of solid organic materials are defined in a similar way [2]
Summary
Cosmology in bimetric theory with an effective composite coupling to matter Gümrükçüo , A.
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