Inflation driven by Scalar-Neutrino coupling in a mass-varying neutrino framework

Abstract We propose a cosmological framework in which neutrino masses evolve dynamically through coupling with a scalar field that simultaneously drives inflation. The neutrino mass is modeled as a power-law, exponential, or hybrid function of the scalar field, yielding an effective potential that includes neutrino backreaction. Starting from the Einstein–Hilbert action in a flat FLRW background, we derive the modified Friedmann and Klein–Gordon equations incorporating this coupling. Using the Fermi–Dirac integrals, we account for the continuous transition of neutrinos from relativistic to nonrelativistic regimes. The inflationary dynamics are investigated through the slow-roll parameters derived from the effective potential, together with the evaluation of the scalar spectral index , and the tensor-to-scalar ratio r for each model. The exponential and mixed MaVaN couplings emerge as the most flexible cases, allowing inflationary dynamics and neutrino mass variation to be accommodated within a single scalar field, only in a constrained region of the parameter space.