Regular Article - Theoretical Physics
Scalar field as a null dust
Department of Physics and Astronomy, Bishop’s University, 2600 College Street, Sherbrooke, Québec, J1M 1Z7, Canada
* e-mail: firstname.lastname@example.org
Accepted: 29 March 2019
Published online: 9 April 2019
We show that a canonical, minimally coupled scalar field which is non-self interacting and massless is equivalent to a null dust fluid (whether it is a test or a gravitating field), in a spacetime region in which its gradient is null. Under similar conditions, the gravitating and nonminimally coupled Brans-Dicke-like scalar of scalar-tensor gravity, instead, cannot be represented as a null dust unless its gradient is also a Killing vector field.
© The Author(s), 2019