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ACT-Planck data and phase transitions from a viable no-scale Standard Model completion

Filippo Cutrona, Francesco Rescigno, and Alberto Salvio

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Phys. Rev. D 114, 043513 – Published 10 August, 2026

DOI: https://doi.org/10.1103/38mz-pw8t

Abstract

Classically scale-invariant (and perturbative) theories provide a way to understand large hierarchies, as scales are generated through dimensional transmutation. They always lead to first-order phase transitions, since symmetries are radiatively broken, and they generically feature quasiflat potentials, which are suitable for inflation. We construct a simple but fully realistic model of this kind that accounts for all observational evidence of new physics and is remarkably compatible with the most recent constraints on inflationary observables from both the Planck/BICEP/Keck and the Atacama Cosmology Telescope Collaborations. This model illustrates how classical scale invariance generically leads to a nonstandard cosmology in which inflation occurs in two stages: a slow-roll stage and a thermal stage, separated by a radiation-dominated era.

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Phys. Rev. D 114, 043513– Published 10 August, 2026
  • Received 3 April 2026
  • Accepted 15 July 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

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