Highly suppressed tensor-to-scalar ratio from a modified Lennard-Jones inflationary potential

The increasingly stringent observational bounds on primordial gravitational waves strongly constrain inflationary model building, favoring scenarios that predict highly suppressed tensor perturbations. While many viable constructions rely on non-canonical kinetic terms, non-minimal couplings, or modifications of gravity, it remains an open question whether comparably small tensor amplitudes can emerge within a minimal, single-field framework driven solely by potential dynamics. In this work we propose a novel inflationary scenario based on a modified Lennard-Jones potential. Inspired by a well-known interaction potential in molecular physics, the proposed form naturally combines a smooth minimum with an extended flat plateau at large field values. This intrinsic structure supports slow-roll inflation and ensures a graceful exit without introducing additional degrees of freedom. We perform a detailed analysis of the inflationary dynamics and confront the model with current observational constraints. We find that the scalar spectral index is fully consistent with CMB data, while the tensor-to-scalar ratio is predicted to be extremely small, reaching values as low as $r\sim10^{-7}$. Finally, the running of the scalar spectral index is also found to be small, well withing the 1$σ$ recent observational bounds from Atacama Cosmology Telescope.

💡 Research Summary

The paper addresses the challenge of achieving an extremely low tensor‑to‑scalar ratio (r) within a minimal, single‑field inflationary framework that relies solely on the potential energy of the inflaton. Inspired by the classic Lennard‑Jones interaction used in molecular physics, the authors construct a modified Lennard‑Jones potential of the form
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