Waves in Scalar-Tensor Theories
Abstract:
Many viable Scalar-Tensor theories for modified gravity introduce scalar
fields that are coupled to matter. The equations that describe the
evolution of the scalar fields are field equations similar to the
Klein-Gordon equation, with additional source terms depending on the
specific model.
The usual way to solve the scalar field equation for a given model, has
been to apply the quasi-static approximation, thus neglecting the time
derivatives and solving it like a Poisson equation. We have developed a
method to integrate the full field equation numerically, allowing for
new phenomena not seen when using the quasi-static approximation.
We present results from our latest research, studying waves arising when
solving the full field equations in spherical symmetry. As examples,
we use the Symmetron model and the Disformally coupled model, where the
propagation of waves has surprising effects. We show how these new
effects can lead to further constraints on the models, and to new
observables.