Enhancement of primordial curvature perturbations in $R^3$-corrected Starobinsky-Higgs inflation

Understand

We provide a systematic study of the Starobinsky-Higgs inflation model in the presence of an additional cubic term of the Ricci scalar.

• We investigate, in particular, the effects of the cubic term on the spectral index $n_s$ and the tensor-to-scalar ratio $r$.
• Through both analytical and numerical analyses, we show that the $R^3$-corrected Starobinsky-Higgs model can achieve compatibility with cosmic microwave background observations while producing distinct observational signatures with different frequency ranges.
• In addition, we discuss the complementarity between different observational probes, including the scalar-induced gravitational waves and spectral distortions, offering an independent probe of the enhanced curvature perturbations.