Eleni I. Manouri | Searcharxiv

arXiv2026

Strong Einstein-Hilbert Gravity Inflation and ACT Phenomenology

In this work we study rescaled effective single scalar field theories, and we confront these with the ACT constraint on the spectral index of the scalar primordial perturbations and the updated BICEP/Planck constraint on the tensor-to-scalar ratio. Rescaled scalar theories of gravity may be the result of an effective $f(R,ϕ)$ gravity at strong curvature regimes, which may result on a rescaling of the Einstein-Hilbert term of the form $\sim αR$. It turns out that canonical scalar field theories with stronger gravity compared to standard Einstein-Hilbert gravity can be compatible with the ACT and updated Planck/BICEP constraints, with stronger gravity meaning that the rescaling parameter $α$ takes values smaller than unity.

gr-qc↗

arXiv2025

Solving the Trans-Planckian Censorship Problem with a Power-law Tail in $R^2$ Inflation: A Dynamical System Approach

In this work we elaborate on solving the trans-Planckian censorship problem of standard slow-roll inflation by using a power-law inflationary tail generated by a scalar field with an exponential potential. We use a quantitative approach by studying in detail the phase space of a combined $F(R,ϕ)$ cosmological system, focusing on the de Sitter and power-law subspaces of the total phase space. As we show, the de Sitter subspace of the $F(R,ϕ)$ system shares the same fixed points as the vacuum $F(R)$ gravity system and the trajectories in the phase space tend to these fixed points. However, the power-law subspace is not stable and cannot be realized by the combined $F(R,ϕ)$ system. To this end, we propose a well-motivated phenomenological $F(R)$ gravity model for which the $R^2$ term is switched off below a critical curvature near the end of the $R^2$ slow-roll inflationary era, and below that critical curvature, only the Einstein-Hilbert gravity term and the scalar field remain in the effective inflationary Lagrangian. The remaining system can successfully realize a power-law tail of the $R^2$ slow-roll era.

gr-qc↗