Eur. Phys. J. C (2025) 85: 1307
https://doi.org/10.1140/epjc/s10052-025-15060-6

Regular Article - Theoretical Physics

Quantum-corrected ${\varphi }^4$ inflation in light of ACT observations

¹ Faculty of Science and Technology, Nakhon Si Thammarat Rajabhat University, 80280, Nakhon Si Thammarat, Thailand
² Informatics Innovation Center of Excellence (IICE) and School of Informatics, Walailak University, 80160, Nakhon Si Thammarat, Thailand
³ Urgench State University, Kh. Alimdjan str. 14, 220100, Urgench, Uzbekistan
⁴ School of Science and College of Graduate Studies, Walailak University, 80160, Nakhon Si Thammarat, Thailand

^a This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 27 August 2025
Accepted: 9 November 2025
Published online: 15 November 2025

Abstract

Recent measurements from the Atacama Cosmology Telescope (ACT), combined with Planck and DESI data, suggest a scalar spectral index $n_s$ higher than the Planck 2018 baseline, thereby placing conventional attractor-type inflationary models such as Starobinsky $R^2$ and Higgs inflation under increasing tension at the $\gtrsim 2\sigma$ level. In this work, we examine quantum-corrected ${\varphi }^4$ inflation with a non-minimal coupling to gravity. Introducing an anomalous scaling parameter $\gamma$ to capture quantum corrections to the effective potential, we derive analytic expressions for the inflationary observables $n_s$ and r. Confronting these predictions with ACT, Planck, and BAO+lensing constraints, we demonstrate that modest values of $\gamma$ can raise $n_s$ into the ACT-preferred range while maintaining a strongly suppressed tensor-to-scalar ratio. For instance, with $N=60$ and $\gamma \simeq 0.006$, the model predicts $n_s\simeq 0.974$ and $r\simeq 0.007$, in excellent agreement with current bounds. We further investigate preheating dynamics, focusing on particle production via parametric resonance in quantum-corrected ${\varphi }^4$ inflation with a non-minimal coupling to gravity. In this scenario, the inflaton $\varphi$ couples to an additional scalar $\chi$ through an interaction $g^2{\varphi }^2{\chi }^2$. In Minkowski spacetime, the resonance dynamics reduce to the Mathieu equation, and we find that broad resonance can be readily achieved, leading to efficient particle production.