ﻻ يوجد ملخص باللغة العربية
We investigate whether there are any cosmological evidences for a scalar field with a mass and coupling to matter which change accordingly to the properties of the astrophysical system it lives in, without directly focusing on the underlying mechanism that drives the scalar field scale-dependent properties. We assume a Yukawa type of coupling between the field and matter and also that the scalar field mass grows with density, in order to overcome all gravity constraints within the solar system. We analyse three different gravitational systems assumed as cosmological indicators: supernovae type Ia, low surface brightness spiral galaxies and clusters of galaxies. Results show that: a) a quite good fit to the rotation curves of low surface brightness galaxies only using visible stellar and gas mass components is obtained; b) a scalar field can fairly well reproduce the matter profile in clusters of galaxies, estimated by X-ray observations and without the need of any additional dark matter; c) there is an intrinsic difficulty in extracting information about the possibility of a scale-dependent massive scalar field (or more generally about a varying gravitational constant) from supernovae type Ia.
In a recent work, we had constructed a model consisting of two fields---a canonical scalar field and a non-canonical ghost field---that had sourced a symmetric matter bounce scenario. The model had involved only one parameter, viz. the scale associat
We present cosmological constraints on the scalar-tensor theory of gravity by analyzing the angular power spectrum data of the cosmic microwave background obtained from the Planck 2015 results together with the baryon acoustic oscillations (BAO) data
The tensor-vector-scalar (TeVeS) model is considered a viable theory of gravity. It produces the Milgroms modified Newtonian dynamics in the nonrelativistic weak field limit and is free from ghosts. This model has been tested against various cosmolog
The first multi-messenger gravitational wave event has had a transformative effect on the space of modified gravity models. In this paper we study the enhanced tests of gravity that are possible with a future set of gravitational wave standard siren
Scalar-tensor theories are frequently only consistent with fifth force constraints in the presence of a screening mechanism, namely in order to suppress an otherwise unacceptably large coupling between the scalar and ordinary matter. Here we investig