Swampland Conjectures through ACT Observations: Observational Signatures of Radiative-Corrected Inflation

TL;DR

This work tests radiatively corrected inflation against ACT DR6+Planck18+BAO within the swampland framework, focusing on FRDSSC, SWGC, and SSWGC. It compares two models: Model I with radiative corrections to Higgs inflation and Model II with a real scalar inflaton coupled to additional scalars and fermions; Model I satisfies FRDSSC but fails SWGC and SSWGC, while Model II satisfies all three conjectures across a sizeable parameter space, with viability depending on the non-minimal coupling ξ and the renormalization scales μ_b and μ_f. Observationally, both models can fit the ACT/Planck bounds on $n_s$ and $r$ with appropriate tuning, but only Model II remains fully consistent with quantum gravity constraints. The study provides a methodology for classifying inflationary scenarios by swampland compatibility and highlights the critical role of radiative corrections in reconciling theory with data.

Abstract

We investigate the consistency of radiatively corrected inflationary models with both the latest observational data from the Atacama Cosmology Telescope (ACT) combined with Planck 2018 and Baryon Acoustic Oscillation (BAO) measurements, and the theoretical constraints imposed by the swampland program. We systematically test two distinct models against three key swampland conjectures: the further refined de Sitter swampland conjecture (FRDSSC), the scalar weak gravity conjecture (SWGC), and the strong scalar weak gravity conjecture (SSWGC). Model I, based on radiatively corrected Higgs inflation, satisfies the FRDSSC and remains consistent with current observational constraints ($n_s = 0.9743 \pm 0.0034$, $r < 0.038$), but fails to meet the SWGC and SSWGC requirements, indicating limited theoretical compatibility with quantum gravity principles. In contrast, Model II, incorporating radiative corrections with scalar sectors, demonstrates full consistency by satisfying all three swampland conjectures simultaneously while maintaining observational viability. The compatibility of Model II is highly sensitive to the non-minimal coupling $ξ$ and renormalization scales $μ_b$, with larger values extending the range of swampland-consistent solutions. Our results highlight the critical role of radiative corrections in achieving simultaneous theoretical and observational consistency, and identify Model II as a promising candidate for a fully viable inflationary scenario within the swampland framework. This work provides a methodology for classifying inflationary models based on their swampland compatibility, demonstrating that satisfaction of the FRDSSC alone is insufficient for full theoretical consistency.

Figures (5)

• Figure 1: SWGC and SSWGC for Model I with respect to $\omega = 9 \times 10^{-10}$, $M_P = 1$. The plots demonstrate that no compatible intervals exist that simultaneously satisfy either the SWGC or the SSWGC for the radiatively corrected Higgs inflation model.
• Figure 2: The compatibility of Model II with SWGC for various values of the renormalization scale $\mu_b$. Higher values of $\mu_b$ expand the allowed parameter intervals, demonstrating enhanced compatibility with swampland constraints.
• Figure 3: The compatibility of Model II with SWGC for different values of the non-minimal coupling $\xi$. The plots illustrate that varying $\xi$ significantly affects the width of the compatible parameter regions.
• Figure 4: The compatibility of Model II with SWGC for a representative set of combined parameters, demonstrating robust satisfaction of the conjecture across the relevant field range.
• Figure 5: The compatibility of Model II with SSWGC for various values of $\xi$: (a) $\kappa_b = 4\times10^{-2}, \kappa_f = 0, \mu_b = 10^{10}, \mu_f= 0, \xi = 1, \lambda_{\phi} = 10^{-1}, M_{P} = 1$; (b) $\kappa_b = 4 \times10^{-2}, \kappa_f = 0, \mu_b= 10^{10}, \mu_f= 0, \xi = 10^{-2}, \lambda_{\phi} = 10^{-1}, M_{P} = 1$; (c) $\kappa_b=4\times10^{-2}, \kappa_f = 0, \mu_b = 10^{10}, \mu_f= 0, \xi=10^{2},\lambda_{\phi}=10^{-1}, M_{P}=1$. These plots demonstrate that Model II maintains SSWGC compatibility across a broad range of $\xi$ values.