Swampland diagnostics and observational tests of the inflationary universe in the Palatini formalism

Abstract

We consider quintessential inflation in a quadratic Palatini model with a generalized Peebles-Vilenkin potential, where the same scalar field describes both the inflationary plateau and the later inverse-power-law regime. Passing to the Einstein frame gives a canonically normalized field and an explicit effective potential. The inflationary predictions are then reassessed, together with the further-refined de Sitter, scalar weak-gravity, strong scalar weak-gravity, distance, and trans-Planckian censorship conjectures. The value of the tensor-to-scalar ratio stays below the observational bounds used in this work, whereas the spectral index of scalar fluctuations changes with the potential exponent and with the duration of inflation. The further-refined de Sitter bound is satisfied only over part of the trajectory. At the pivot, both weak-gravity diagnostics are negative in the reduced-Planck-mass convention, although they become positive at finite field values. The field excursion is super-Planckian, but this does not by itself imply a failure of the distance conjecture; the trans-Planckian censorship criterion is not met in the assumed slow-roll regime.