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arXiv · 2510.15609

Signals from Fermionic inflationary cosmology with Yukawa interaction

Lin-Hong Sui·Dan Li·Jia-Ze Sun·Xi-Bin Li
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Abstract

We investigate an inflationary model wherein the Dirac field $\psi$ is directly coupled to a scalar inflaton $\phi$ via a Yukawa interaction $g\phi\bar\psi\psi$ and examine the resulting observational implications. Within the slow-roll approximation, we derive analytical solutions of the Dirac equations during inflation. The analytical result on the fermion pair density $\langle n\rangle$ indicates that the Yukawa interaction strength $g$ is to characterize the degree of non-adiabaticity. For large value of the dimensionless effective mass $\tilde m=(m+g\phi)/H$, i.e. $\tilde m\gtrsim 1$, the tensor-to-scalar ratio $r$ is suppressed by a factor of approximately $1/(1+2.95\pi^2g^2)$. This condition is also characterized by a significant backreaction. Conversely, if $\tilde m \ll 1$, the value of $r$ remains consistent with that observed in standard cold inflation. Our analysis is performed under the assumption of the highest inflationary energy scales compatible with current observational constraints.

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Lin-Hong Sui, Dan Li, Jia-Ze Sun, Xi-Bin Li. 2025-10-17. Signals from Fermionic inflationary cosmology with Yukawa interaction. https://arxiv.org/abs/2510.15609

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