Ilias C. Papadimitriou

arXiv2023

Swampland Criteria and Constraints on Inflation in a $f(R,T)$ Gravity Theory

In this paper, we worked in the framework of an inflationary $f(R,T)$ theory, in the presence of a canonical scalar field. More specifically, the $f(R,T)=γR+2καT$ gravity. The values of the dimensionless parameters $α$ and $γ$ are taken to be $α\geq 0$ and $0 < γ\leq 1$. The motivation for that study was the striking similarities between the slow-roll parameters of the inflationary model used in this work and the ones obtained by the rescaled Einstein-Hilbert gravity inflation $f(R)=αR$. We examined a variety of potentials to determine if they agree with the current Planck Constraints. In addition, we checked whether these models satisfy the Swampland Criteria and we specified the exact region of the parameter space that produces viable results for each model. As we mention in Section IV the inflationary $f(R,T)$ theory used in this work can not produce a positive $n_T$ which implies that the stochastic gravitational wave background will not be detectable.

gr-qc↗

arXiv2022

Bottom-Up Reconstruction of Viable GW170817 Compatible Einstein-Gauss-Bonnet Theories

In this work we shall use a bottom-up approach for obtaining viable inflationary Einstein-Gauss-Bonnet models which are also compatible with the GW170817 event. Specifically, we shall use a recently developed theoretical framework in which we shall specify only the tensor-to-scalar ratio, in terms of the $e$-foldings number. Starting from the tensor-to-scalar ratio, we shall reconstruct from it the Einstein-Gauss-Bonnet theory which can yield such a tensor-to-scalar ratio, finding the scalar potential and the Gauss-Bonnet coupling scalar function as functions of the $e$-foldings number. Accordingly, the calculation of the spectral index of the primordial scalar perturbations, and of the tensor spectral index easily is greatly simplified and these observational indices can easily be found. After presenting the general formalism for the bottom-up reconstruction, we exemplify our findings by presenting several Einstein-Gauss-Bonnet models of interest which yield a viable inflationary phenomenology. These models have also an interesting common characteristic, which is a blue tilted tensor spectral index. We also investigate the predicted energy spectrum of the primordial gravitational waves for these Einstein-Gauss-Bonnet models, and as we show, all the models yield a detectable primordial wave energy power spectrum.

gr-qc↗