We investigate warm inflationary scenario in which the accelerated expansion of the early Universe is driven by chameleon-like scalar fields. Due to the non-minimal coupling between the scalar field and the matter sector, the energy-momentum tensor of each fluid component is not conserved anymore, and the generalized balance equation is obtained. The new source term in the energy equation can be used to model warm inflation. On the other hand, if the coupling function varies slowly, the model reduces to the standard model used for the description of cold inflation. To test the validity of the warm chameleon inflation model, the results for warm inflationary scenarios are compared with the observational Planck2018 Cosmic Microwave Background data. In this regard, the perturbation parameters such as the amplitude of scalar perturbations, the scalar spectral index and the tensor-to-scalar ratio are derived at the horizon crossing in two approximations, corresponding to the weak and strong dissipative regimes. As a general result it turns out that the theoretical predictions of the chameleon warm inflationary scenario are consistent with the Planck 2018 observations.

In this study, the scenario of a two-component warm tachyon inflation is considered, where the tachyon field plays the role of the inflaton by driving the inflation. During inflation, the tachyon scalar field interacts with the other component of the Universe, which is assumed to be photon gas, i.e., radiation. The interacting term contains a dissipation coefficient, and the study is modeled based on two different and familiar choices of the coefficient that were studied in the literature. By employing the latest observational data, the acceptable ranges for the free parameters of the model are obtained. For any choice within the estimated ranges, there is an acceptable concordance between the theoretical predictions and observations. Although the model is established based on several assumptions, it is crucial to verify their validity for the obtained values of the free parameters of the model. It is found that the model is not self-consistent for all values of the ranges, and for some cases, the assumptions are violated. Therefore, to achieve both self-consistency and agreement with the data, the parameters of the model must be constrained. Subsequently, we consider the recently proposed swampland conjecture, which imposes two conditions on the inflationary models. These criteria rule out some inflationary models; however, warm inflation is among those that successfully satisfy the swampland criteria. We conduct a precise investigation, which indicates that the proposed warm tachyon inflation cannot satisfy the swampland criteria for some cases. In fact, for the first case of the dissipation coefficient, in which, there is dependency only on the scalar field, the model agrees with observational data. However, it is in direct tension with the swampland criteria. Nevertheless, for the second case, wherein the dissipation coefficient has a dependency on both the scalar field and temperature, the model exhibits acceptable agreement with observational data, and suitably satisfies the swampland criteria.

The scenario of constant-roll inflation in the framework of a noncanonical inflaton model is studied. Both of these modifications lead to the appearance of some differences in the slow-roll parameters besides the Friedmann equations, resulting in a better justification of theoretical predictions compared to observations. Phenomenologically, by assuming a constant $\eta$, i.e., a second slow-roll parameter, and recalculating the related perturbation equations, obviously there should appear some modification in the scalar spectral index and amplitude of scalar perturbations. It is shown that finding an exact solution for the Hubble parameter is one of the main advantages and triumphs of this approach. Also, whereas making a connection between subhorizon and super-horizon regions has a crucial role in inflationary studies, the main perturbation parameters are obtained at the horizon crossing time. To examine the accuracy of our results, we consider the Planck 2018 results as a confident criterion. To do so by virtue of the $r-n_s$ diagram, the acceptable ranges of the free parameters of the model are illustrated. As a result, it is found that the second slow-roll parameter should be a positive constant and smaller than unity. By constraining the free parameters of the model, also, an energy scale of inflation is estimated that is of order ${10}^{-2}$. Even more, by investigating the attractor behavior of the model, it is clear that the aforementioned properties can be appropriately satisfied.

The post Newtonian parameter is considered in the chameleon-Brans-Dicke model. In the first step, the general form of this parameter and also effective gravitational constant is obtained. An arbitrary function for $f(\Phi )$, which indicates the coupling between matter and scalar field, is introduced to investigate validity of solar system constraint. It is shown that the chameleon-Brans-Dicke model can satisfy the solar system constraint and gives us an $\omega$ parameter of order ${10}^4$, which is in comparable to the constraint which has been indicated in 19. DOI: http://dx.doi.org/10.1103/PhysRevD.83.104019 © 2011 American Physical Society