Limited modified gravity

Modified gravity and cosmology

Viscosity in Modified Gravity

A bulk viscosity is introduced in the formalism of modified gravity. It is shown that, based on a natural scaling law for the viscosity, a simple solution can be found for quantities such as the Hubble parameter and the energy density. These solutions may incorporate a viscosity-induced Big Rip singularity. By introducing a phase transition in the cosmic fluid, the future singularity can nevert...

Nonderivative modified gravity: a classification

We analyze the theories of gravity modified by a generic nonderivative potential built from the metric, under the minimal requirement of unbroken spatial rotations. Using the canonical analysis, we classify the potentials V according to the number of degrees of freedom (DoF) that propagate at the nonperturbative level. We then compare the nonperturbative results with the perturbative DoF propag...

Dark energy versus modified gravity.

There is now strong observational evidence that the expansion of the Universe is accelerating. The standard explanation invokes an unknown "dark energy" component. But such scenarios are faced with serious theoretical problems, which has led to increased interest in models where instead general relativity is modified in a way that leads to the observed accelerated expansion. The question then a...

Mass Screening in Modified Gravity

Models of modified gravity introduce extra degrees of freedom, which for consistency with the data, should be suppressed at observable scales. In the models that share properties of massive gravity such a suppression is due to nonlinear interactions: An isolated massive astrophysical object creates a halo of a nonzero curvature around it, shielding its vicinity from the influence of the extra d...