Slow-roll Natural & Hilltop Inflation in Rastall Gravity

Isaac M. Vitohekpon; Biswajit Deb; Ines G. Salako; V. A. Monwanou; Atri Deshamukhya

doi:10.1016/j.hedp.2025.101238

paper

Slow-roll Natural & Hilltop Inflation in Rastall Gravity

arXiv:2503.23172 · doi:10.1016/j.hedp.2025.101238

Abstract

This study provides a concise analysis of inflation under Rastall gravity by examining three types of potential such as the power law, natural, and hilltop potentials. Choosing a minimal interaction between matter and gravity, we derived the modified slow-roll parameters, the scalar spectral index $(n_{s})$ , the tensor spectral index $(n_{T})$ , and the tensor-to-scalar ratio $(r)$ . For a general power-law potential as well as for Natural & Hilltop inflation, we calculated these quantities and subsequently plotted their trajectories in the $(n_{s}, r)$ plane. For the power-law potential, only the cases $n = 2/3$ and $n = 1$ satisfy the observational constraint of the Planck 2018 data. The natural potential analysis shows that the mass scale is crucial, with better compatibility achieved at $f = 5 M_{p}$ compared to $f = 10 M_{p}$ . Lastly, the Hilltop potential results indicate that among the cases studied $m = 3/2, 2, 3$ , and $4$ , only $m = 3/2$ exhibits marginal consistency with observational bounds, while the other cases fail to produce acceptable $(n_{s} - r)$ trajectories.

17 pages, 10 figures

Slow-roll Natural & Hilltop Inflation in Rastall Gravity

Abstract

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