Signals from Fermionic inflationary cosmology with Yukawa interaction

We investigate an inflationary model wherein the Dirac field ψ is directly coupled to a scalar inflaton ϕ via a Yukawa interaction g ϕ ψ ¯ ψ 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 〈 n 〉 indicates that the Yukawa interaction strength g is to characterize the degree of non-adiabaticity. For large value of the dimensionless effective mass m ˜ = ( m + g ϕ ) / H , i.e. m ˜ ≳ 1 , the tensor-to-scalar ratio r is suppressed by a factor of approximately 1 / ( 1 + 2.95 π 2 g 2 ) . This condition is also characterized by a significant backreaction. Conversely, if m ˜ ≪ 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.