Abstract
We propose a scenario that can naturally explain the observed dark matter-baryon ratio in the context of bimetric theory with a chameleon field. We introduce two additional gravitational degrees of freedom, the massive graviton and the chameleon field, corresponding to dark matter and dark energy, respectively. The chameleon field is assumed to be non-minimally coupled to dark matter, i.e., the massive graviton, through the graviton mass terms. We find that the dark matter-baryon ratio is dynamically adjusted to the observed value due to the energy transfer by the chameleon field. As a result, the model can explain the observed dark matter-baryon ratio independently from the initial abundance of them.
Highlights
Cosmological observations have confirmed the big bang cosmology and determined the cosmological parameters precisely [1]
We have added two new ingredients to the standard model: the massive graviton and the chameleon field corresponding to dark matter and dark energy, respectively
The matter fields are minimally coupled to the Jordan frame metric which leads to the nonminimal coupling of the matter fields to the chameleon field
Summary
Cosmological observations have confirmed the big bang cosmology and determined the cosmological parameters precisely [1]. We shall combine two ideas of the modifications of gravity by using the proposal of [17]: the nonminimal coupling of φ and the existence of the massive graviton. We promote parameters in the graviton mass terms to functions of φ [18,19], giving rise to a new type of coupling between φ and dark matter In this case, as discussed in [17], the field value of φ depends on the environment due to the nonminimal coupling as with the. If the potential of φ is designed to be dark energy, the chameleon field φ can give rise to the present acceleration of the universe Both dark energy and dark matter are explained by the modifications of gravity in our model.
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