Phantom Behavior in Chameleon Brans-Dicke Theory

Abstract

We consider a generalized Brans-Dicke model in which the scalar field has a potential function and is allowed to couple non-minimally with the matter part. We then assume that the scalar field is a chameleon field. We find an asymptotic late-time solution which exhibits late-time accelerating expansion for large and positive Brans-Dick parameter. The solution indicates that the chameleon appears as a phantom field. We argue that the second law of thermodynamics constrains the direction of energy transfer between the scaler field and the matter system.