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We study antigravity, that is, having an effective gravitational constant with a negative sign, in scalar-tensor theories originating from

During the last two decades our perception about the universe has changed drastically owing to the discovered late time acceleration that our universe has. Particularly, it can be thought as one of the most striking astrophysical observations with another striking observation being the verification of the inflating period of our universe. Actually, moving from time zero to present time, inflation came first, with the late time acceleration occurring at present epoch. One of the greater challenges in cosmology is to model this late time acceleration in a self-consistent way. According to the new Planck telescope observational data for the present epoch, the universe is consistently described by the

One of the most promising and theoretically appealing descriptions of dark energy and late time acceleration issues is provided by the

In principle, every consistent generalization of general relativity inevitably has to be confronted with the successes of general relativity. Since general relativity is a successful description of nature in strong gravitational environments, there exist a large number of constraints that need to be satisfied, in order that an

In theories of modified gravity a longstanding debatable theoretical problem exists, related to Jordan and Einstein frames [

This paper is organized as follows: in Section

In this section in order to maintain the paper self-contained, we briefly review the main features of

The geometrical background of the manifolds used here is pseudo-Riemannian and is described locally by a Lorentz metric (the FRW metric in our case), in addition to a torsionless, symmetric, and metric compatible affine connection, the so-called Levi-Civita connection. In such a geometric background, the Christoffel symbols are

The most striking feature of the

There exists another degree of freedom in

The possibility of antigravity sectors in

It is a quite well-known fact that scalar-tensor theories are equivalent to

In this paper we will use a variant but quite similar method to obtain an antigravity scalar-tensor theory starting from a given

As an application of the method we just presented, let us use a viable

The model we studied in this section is similar to the one studied in [

Before we close this section, we discuss an important issue. Reasonably, it can be argued that since the effective gravitational constant

As we saw in the previous section, even though we started from an

Brans-Dicke model with cosmological constant: time dependence of the scalar field

Brans-Dicke model with cosmological constant: the effective gravitational constant

Before closing this section, we discuss a last issue of some importance. It is generally known that a general

In this paper we studied antigravity in scalar-tensor theories originating from

Finally, it is worth discussing the results and also the cosmological implications of our results. The main goal of this paper was to demonstrate all possible cases in which antigravity might appear in modified theories of gravity. As we explicitly demonstrated, in the case of

The authors declare that there is no conflict of interests regarding the publication of this paper.