Analysis of repulsive central universal force field on solar and galactic dynamics

Recent astrophysical observations hint toward the need for an extended theory of gravity to explain puzzles presented by the standard cosmological model such as the need for dark matter and dark energy to understand the dynamics of the cosmos. This paper investigates the effect of a repulsive central universal force field on the behavior of celestial objects. Negative tidal effect on the solar and galactic orbits, like that experienced by Pioneer spacecrafts, was derived from the central force and was shown to manifest itself as dark matter and dark energy. Vertical oscillation of the sun about the galactic plane was modeled as simple harmonic motion driven by the repulsive force. The proposed universal field was used to infer the shape of dark matter halos as generated from a planar component of the universal force and to explain galactic warp, galactic halo density, and galactic rotation curves. It was found that the repulsive field addition to Newton’s gravity mimics the Yukawa potential correction employed by many current gravitational theories that modify gravity.

What laboratory experiments can teach us about cosmology: A chameleon example

Laboratory experiments can shed light on theories of new physics introduced in order to explain cosmological mysteries, including the nature of dark energy and dark matter. In this article I will focus on one particular example of this, the chameleon model. The chameleon is an example of a theory which could modify gravity on cosmological distance scales, but its non-linear behavior means that it can also be tested with suitably designed laboratory experiments. The aim of this overview is to present recent theoretical developments to the experimental community.

Cosmological constant

The contribution of vacuum fluctuations to the cosmological constant is reconsidered studying the dependence on the used regularisation scheme. Then alternative explanations for the observed accelerated expansion of the universe in the present epoch are introduced which either modify gravity or add a new component of matter, dubbed dark energy. The chapter closes with some comments on attempts to quantise gravity.

OBSERVABLE CONSEQUENCES OF STRONG COUPLING IN THEORIES WITH LARGE DISTANCE MODIFIED GRAVITY

In this talk, we review theories that modify gravity at cosmological distances, and show that any such theory must exhibit a strong coupling phenomenon. We show that all consistent theories that modify the dynamics of the spin-2 graviton on asymptotically flat backgrounds, automatically have this property. Due to the strong coupling effect, modification of the gravitational force is source-dependent, and for lighter sources sets in at shorter distances. This universal feature makes modified gravity theories predictive and potentially testable by precision gravitational measurements at scales much shorter than the current cosmological horizon.

THEORY AND PHENOMENOLOGY OF DGP GRAVITY

I review some aspects of the Dvali–Gabadadze–Porrati (also known as "brane-induced") model of gravity. This model provides a novel way to modify gravity at large distances and, as such, has potentially some interesting cosmological consequences, like the possibility of getting an accelerated expansion with a vanishing cosmological constant. In DGP gravity, the recovery of usual gravitational interaction at small (i.e. noncosmological) distances is rather nontrivial. This can lead to observable signature in observations made in the solar system. I discuss various aspects of the phenomenology of the model and briefly comment on the consistency of the whole approach.