Item

Abstract

The Swampland de Sitter conjecture in combination with upper limits on the tensor-to-scalar ratio r derived from observations of the cosmic microwave background endangers the paradigm of slow-roll single field inflation. This conjecture constrains the first and the second derivatives of the inflationary potential in terms of two (1) constants c and c′. In view of these restrictions we reexamine single-field inflationary potentials with S-duality symmetry, which ameliorate the unlikeliness problem of the initial condition. We compute r at next-to-leading order in slow-roll parameters for the most general form of S-dual potentials and confront model predictions to constraints imposed by the de Sitter conjecture. We find that c∼(10−1) and c′∼(10−2) can accommodate the 95\% CL upper limit on r. By imposing at least 50 e-folds of inflation with the effective field theory description only valid over a field displacement (1) when measured as a distance in the target space geometry, we further restrict c∼(10−2), while the constraint on c′ remains unchanged. We comment on how to accommodate the required small values of c and c′.