In this work we investigate curvature perturbations and non-Gaussianity arising from Higgs modulated reheating in the early Universe. We employ three different methods—the period-averaging (PA) method, the exact method, and the nonperturbative $\delta N$ formalism—to compute the power spectrum and bispectrum of curvature perturbations. Our results show that the nonperturbative $\delta N$ method provides a reliable estimate across a wide range of reheating time and Higgs field values, including regimes where the Higgs field oscillates significantly after inflation. We find that a smaller Higgs self-coupling ($\lambda$) leads to a larger curvature perturbation, with the non-Gaussianity predominantly taking a local shape. This highlights the importance of considering nonperturbative effects in calculating the curvature perturbation during Higgs modulated reheating, especially for smaller values of $\lambda$. Our findings offer valuable insights into the dynamics of reheating and the generation of primordial perturbations in the early Universe.

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• Cosmic microwave background
• Cosmology
• Inflation
• Large scale structure of the Universe