Inflationary models in a minimally coupled $f(R,T)$ gravity: Constraints from $Planck$, BICEP/$Keck$, and ACT

Abstract

The advent of high-precision cosmological observations has challenged many traditional inflationary models. Data from $Planck$ 2018 along with the BICEP/$Keck$ 2018 result have already ruled out most of the established models by placing tight constraints on the tensor-to-scalar ratio $r$. Upcoming missions like LiteBIRD & CMB-S4 are expected to impose an even more stringent bound on $r$, potentially excluding further models from the viable landscape. In this evolving observational context, modified gravity theories offer a promising way to reconcile inflationary models with data. In this work, we explore several inflationary models, namely mutated hilltop inflation, D-brane inflation, and Woods-Saxon inflation, within the framework of $f(R,T)$ gravity. A minimally coupled and linear combination of Ricci scalar and trace of EM tensor is considered as $f(R,T)=R+16\pi G\lambda T$ and the cosmological observable parameters, viz. scalar spectral tilt $n_s$, tensor-to-scalar ratio $r$, and running of scalar spectral index $n_{sk}$ are estimated for the three models, and their trajectories are plotted in the $n_s-r$ plane. The model results are evaluated in light of the $Planck$, BICEP/$Keck$, DESI DR2, and ACT DR6 data. We observe that for a certain model parameter space, these potentials are viable within the current observational bounds.

22 pages, 6 figures, 2 tables, Accepted version

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