Curvature Perturbations from Higgs Modulated Reheating

TL;DR

This work investigates curvature perturbations from Higgs modulated reheating by comparing three computational approaches: the period-averaging (PA) method, an exact x-space method, and a non-perturbative $\delta N$ formalism. It demonstrates that the non-perturbative $\delta N$ method reliably predicts both the power spectrum and the bispectrum across a wide range of reheating times and Higgs field values, even when the Higgs oscillates strongly after inflation. A key finding is that smaller Higgs self-coupling $\lambda$ enhances the curvature perturbations and that the resulting non-Gaussianity is predominantly of local type; Higgs self-interactions can also contribute significantly to non-Gaussianity, especially for larger $\lambda$. The study clarifies the regimes of validity for PA and naive $\delta N$, highlights the importance of non-perturbative effects in Higgs-modulated reheating, and provides detailed mappings of how reheating dynamics shape primordial perturbations.

Abstract

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 non-perturbative $δN$ formalism -- to compute the power spectrum and bispectrum of curvature perturbations. Our results show that the non-perturbative $δN$ 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 ($λ$) leads to a larger curvature perturbation, with the non-Gaussianity predominantly taking a local shape. This highlights the importance of considering non-perturbative effects in calculating the curvature perturbation during Higgs modulated reheating, especially for smaller values of $λ$. Our findings offer valuable insights into the dynamics of reheating and the generation of primordial perturbations in the early Universe.

Figures (9)

• Figure 1: The power spectrum of curvature perturbation calculated in four different methods in the $(\omega, \mathcal{P}_\zeta^{(h)}/A_h^4)$ plane.
• Figure 2: The power spectrum of curvature perturbation calculated in three different methods in the $(t_\mathrm{reh}, \mathcal{P}_\zeta^{(h)})$ plane.
• Figure 3: The three-point function of curvature perturbation calculated using exact and non-perturbative $\delta N$ methods.
• Figure 4: The reduced bispectrum of curvature perturbation calculated in period-averaging and non-perturbative $\delta N$ method.
• Figure 5: The power spectrum of curvature perturbation with different $\lambda$ calculated in non-perturbative $\delta N$ method.