Beyond self-acceleration: force- and fluid-acceleration

Understand

The notion of self-acceleration has been introduced as a convenient way to theoretically distinguish cosmological models in which acceleration is due to modified gravity from those in which it is due to the properties of matter or fields.

• In this paper we review the concept of self-acceleration as given, for example, by [1], and highlight two problems.
• First, that it applies only to universal couplings, and second, that it is too narrow, i.e.
• it excludes models in which the acceleration can be shown to be induced by a genuine modification of gravity, for instance coupled dark energy with a universal coupling, the Hu-Sawicki f(R) model or, in the context of inflation, the Starobinski model.