arXiv subjects

Feng-Yi Zhang

Publications and source records attributed to Feng-Yi Zhang.

3 recordsLinked to original sources

arXiv2026

Probing the Perturbative Reheating History of Decaying Oscillatory Inflation with ACT Constraints

Precision measurements of the Cosmic Microwave Background (CMB) now offer a powerful probe of the unknown reheating epoch. In this work, we scrutinize a decaying oscillatory inflation model inspired by supergravity, replacing standard ad hoc reheating assumptions with a fully dynamical calculation based on perturbative inflaton decay. By numerically tracking the energy transfer and the evolution of the equation of state, we eliminate the theoretical degeneracy associated with the reheating duration, directly linking the microphysical decay rate $Γ$ to the observable spectral index $n_s$. We confront these self-consistent predictions with the combined constraints from Planck 2018 and ACT DR6. Our analysis demonstrates that the viable parameter space is tightly bracketed: the thermalization requirement from Big Bang Nucleosynthesis imposes a strict lower bound on the coupling strength, while the latest ACT data strongly favor scenarios with efficient reheating ($T_{\text{re}} \gtrsim 10^{14}$ GeV), effectively pushing the model towards the instantaneous reheating limit. This study highlights the capability of modern CMB data to constrain the particle physics nature of the early universe.

astro-ph.CO↗

arXiv2026

Reconciling the ACT Preference in $f(T)$ Gravity: Inflation and Reheating Constraints

Compared with the results of Planck-only analyses, recent measurements from the Atacama Cosmology Telescope (ACT) indicate a preference for a slightly bluer scalar spectral index, placing canonical inflationary models in General Relativity (GR) under mild pressure. We demonstrate that $f(T)$ gravity systematically accommodates these dataset-dependent preferences by suppressing the tensor-to-scalar ratio in monomial and hilltop potentials, and by shifting the spectral index of E-models toward the ACT-favored region. Incorporating Big Bang Nucleosynthesis bounds, we break the degeneracy between the inflationary $e$-folding number and the post-inflationary thermal history. A direct side-by-side comparison reveals that reconciling models such as the Starobinsky potential with ACT data in GR strictly necessitates a non-standard, stiff (kinetic-dominated) reheating phase. In contrast, torsional corrections in $f(T)$ gravity significantly enlarge the viable parameter space, relaxing these stringent phenomenological requirements and establishing a coherent framework that jointly constrains CMB observables and reheating dynamics.

gr-qc↗

arXiv2025

Frame-Dependence of the Hamilton-Jacobi Formalism for Inflation and Reheating in Non-Minimal Gravity

In this work, we investigate the Hamilton-Jacobi formalism for non-minimally coupled inflation, focusing on the methodological frame-dependence arising from its application in the Jordan and Einstein frames. We systematically compare the physical predictions from two distinct computational schemes: applying the Hamilton-Jacobi approximation before versus after the conformal transformation. This comparison is conducted for both the metric and Palatini formalisms. Our results, consistent with Planck data, reveal significant quantitative differences between the two schemes, highlighting a subtle frame-dependence in the approximation method. These discrepancies, observed in the spectral index, the tensor-to-scalar ratio, and reheating parameters, are more pronounced in the Palatini formalism. Our study emphasizes the sensitivity of cosmological predictions to the computational path chosen, and provides a quantitative analysis of this methodological uncertainty, offering valuable insights into the robustness of predictions in modified gravity.

gr-qc↗