We investigate, in the framework of a recently introduced new class of invariant geometrical scalar–tensor theory of gravity, the possibility that a viscous dark fluid can be described in a unified manner by a single scalar field. Thus we developed a model in which both the metric tensor and the scalar field have geometrical origin. The scalar field is characterized by a non-canonical kinetic term and the scalar viscosity of the dark fluid appears as soon the kinetic energy of the scalar field is no longer canonical. The scalar viscosity is considered as a function of the Hubble and the deceleration parameters. To illustrate the formalism we have considered two cases: a constant and a thermodynamic equation of state parameters. In the both cases we obtain analytic representations for the scalar field and their respective potentials. We delimit free parameters by comparing with some Planck 2018 results.

我们在最近引入的一类新的不变几何标量-张量引力理论的框架内研究了粘性暗流体可以由单个标量场以统一方式描述的可能性。因此，我们开发了一个模型，其中度量张量和标量场都具有几何原点。标量场的特征是非规范的动力学项，并且一旦标量场的动能不再规范，就会出现深色流体的标量粘度。标量粘度被认为是哈勃和减速参数的函数。为了说明形式主义，我们考虑了两种情况：常数和状态参数的热力学方程。在这两种情况下，我们都获得了标量场及其各自势能的解析表示。