A scalar-tensor cosmological model with dynamical light velocity

Abstract

Abstract. The dynamical consequences of a bimetric scalar-tensor theory of gravity with a dynamical light speed are investigated in a cosmological setting. The model consists of a minimallycoupled self-gravitating scalar field coupled to ordinary matter fields in the standard way through the metric: gµν +B∂µφ∂νφ. We show that in a universe with matter that has a radiation-dominated equation of state, the model allows solutions with a de Sitter phase that provides sufficient inflation to solve the horizon and flatness problems. This behaviour is achieved without the addition of a potential for the scalar field, and is shown to be largely independent of its introduction. We therefore have a model that is fundamentally different than the potential-dominated, slowly-rolling scalar field of the standard models inflationary cosmology. The speed of gravitational wave propagation is predicted to be significantly different from the speed of matter waves and photon propagation in the early universe.

Comments on “Note on varying speed of light theories”

“…For example, in bimetric models [9,10,11,12] there is never any ambiguity in what to do with any component of the matter action, electromagnetic or otherwise. Simply write the theory, as before, making sure you use the matter rather than the gravity metric.…”

“…This was the route followed in early VSL papers [4,5] and in bimetric theories [9,10,11,12,13,14,15]. But it is not true that a theory has to be defined by a Lagrangian or a Hamiltonian.…”

Fluctuation Spectrum From a Scalar-Tensor Bimetric Gravity Theory

“…The model that we introduced in [2,1] consisted in a minimally-coupled, self-gravitating biscalar field φ coupled to matter through what we refer to as the "matter metric":…”

“…Recently we have introduced a cosmological model [2,1], based on a scalar-tensor bimetric gravitational theory (BGT) in which the relative propagation velocities of gravitational and matter disturbances is determined dynamically. In the resulting diffeomorphism invariant theory there is a prior-geometric relationship between two metrics that involves the gradient of a scalar field.…”

“…Due to its role in producing a theory with multiple light cones (or birefringent spacetimes), the scalar field is referred to as the "biscalar" field. Depending on the choice of frame, spacetimes may either be viewed as having a fixed speed of light and a dynamically-determined speed of gravitational disturbances, or as having a fixed speed of gravitational waves and a dynamical speed of light [2,1,5]. The BGT cosmological model was shown to possess solutions that had sufficient inflation to solve the horizon and flatness problems, and in order to bring it in line with current observations on the CMB radiation, we now demonstrate that it is capable of generating an approximately scale invariant primordial scalar perturbation spectrum.…”