We discuss how the non-minimal coupling ξφ 2 R between the inflaton and the Ricci scalar affects the predictions of single field inflation models where the inflaton has a non-zero vacuum expectation value (VEV) v after inflation. We show that, for inflaton values both above the VEV and below the VEV during inflation, under certain conditions the inflationary predictions become approximately the same as the predictions of the Starobinsky model. We then analyze inflation with double-well and Coleman-Weinberg potentials in detail, displaying the regions in the v-ξ plane for which the spectral index n s and the tensor-to-scalar ratio r values are compatible with the current observations. r is always larger than 0.002 in these regions. Finally, we consider the effect of ξ on small field inflation (hilltop) potentials.

The methods of supergravity allow us to derive a multi-field F-term potential. Using this, we denote a generic and non-positive single-field F-term potential. We insert our theory into the scalar-gravity part of the (2,1|1) invariant superconformal action. That action leads us to a de Sitter solution at the inflationary trajectory. One can denote stabilization of fields in terms of the Kähler kinetic terms and single-field slow-roll inflation parameters. We combine these with the de Sitter swampland conjecture to generate a bounded conjecture. This approach allowed us to show that the single field slow-roll inflation works in harmony with bounded de Sitter conjecture for any concave inflation potential.

In this work, we present an effective field theory for string inflation with spontaneously broken supersymmetry without generating any supersymmetric anti-de Sitter vacua. In that regard, we analyze the nilpotent superfields that effectively capture the physics of anti-D3 branes, and obtain the underlying pattern of universal attractors with a single parameter. Accordingly, we reveal a novel uplifting method by adding the same parameter as a complex contribution parallel to the decomposition of a superfield. Following that, we obtain an almost vanishing cosmological constant in a region where the inflationary attractors unify. Finally, we show that the introduction of nilpotent superfields drastically extends the string landscape for the de Sitter (swampland) conjecture, and the (super)universal attractors are in the string landscape in that respect.

We investigate the Trans-Planckian Censorship Conjecture (TCC) and the arising bounds on the inflationary cosmology caused by that conjecture. In that investigation, we analyze TCC bounds for both Jordan and Einstein frames in the presence of a generic non-minimal coupling (to gravity) term. That term allows us to use the functional freedom it brings to the inflationary Lagrangian as an effective Planck mass. In this sense, we argue one should consider the initial field value of the effective Planck mass for the TCC. We show that as a result, one can remove the TCC upper bounds without the need to produce a new process or go beyond the standard inflation mechanism, with the generalized non-minimal coupling, and for Higgs-like symmetry-breaking potentials.

In this work, we present an effective field theory for string inflation with spontaneously broken supersymmetry without generating any supersymmetric anti-de Sitter vacua. In that regard, we analyze the nilpotent superfields that effectively capture the physics of anti-D3 branes, and obtain the underlying pattern of universal attractors with a single parameter. Accordingly, we reveal a novel uplifting method by adding the same parameter as a complex contribution parallel to the decomposition of a superfield. Following that, we obtain an almost vanishing cosmological constant in a region where the inflationary attractors unify. Finally, we show that the introduction of nilpotent superfields drastically extends the string landscape for the de Sitter (swampland) conjecture, and the (super)universal attractors are in the string landscape in that respect.