Smooth hybrid inflation in light of ACT DR6 data

TL;DR

The paper revisits smooth hybrid inflation in light of the ACT DR6 measurement $n_s ≈ 0.974$, addressing the tension between hybrid models and topological defects. By letting the power $m$ of nonrenormalizable terms vary, the authors show the predicted spectral index remains $n_s ≈ 0.97$ across models, while the tensor-to-scalar ratio is negligibly small. They derive the effective inflaton potential, analyze slow-roll dynamics, and characterize postinflationary evolution, including reheating temperatures and baryogenesis pathways, as well as a Higgsino-like dark-matter candidate. The work demonstrates that a defect-free hybrid inflation scenario can be fully compatible with the latest CMB data and cosmological considerations for baryogenesis and dark matter.

Abstract

Smooth hybrid inflation is a hybrid inflation model which is free from topological defects and predicts the density perturbation with the spectral index of about $0.97$. We show that the prediction on the spectral index is robust regardless the power of nonrenormalizable terms and meets with the latest results reported by Atacama Cosmology Telescope. Viable scenarios for baryogenesis and dark matter are also discussed.

Figures (3)

• Figure 1: Contours of $\sigma(N)/\sigma_t$ for $N=60$. The gray shaded region violates the condition (\ref{['enq:sigma']}).
• Figure 2: Cutoff scale $M$ dependence on the tensor to scalar ratio for $m=2$. The thicker line is for $N=60$, while the thinner line is for $N=50$.
• Figure 3: Model prediction for $M=10^{-3}$. The thicker blue curve is for $N=60$, while the thinner blue curve is for $N=50$.