Are single-field models of inflation and PBHs production ruled out by ACT observations?

2025/05/23 by Daniel Frolovsky, Frolovsky, Daniel, Sergei V. Ketov +1 · 10 citations
Physics and Astronomy · Earth and Planetary Sciences · #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #General Relativity and Quantum Cosmology (gr-qc)

paper · doi:10.48550/arxiv.2505.17514

Abstract

The data release from the Atacama Cosmology Telescope (ACT) imposes stronger constraints on primordial black holes (PBHs) formation in single-field inflation models versus the Planck data. In particular, the updated Cosmic Microwave Background (CMB) radiation measurements favour a \it higher scalar spectral index n_s and its \it positive running α_s, which put the single-field models under scrutiny. Even in the absence of PBHs production, the new data constrain many single-field models of inflation. To explore this tension, we study PBHs formation in a concrete viable α-attractor E-model. We investigate an impact of bending of the inflaton potential plateau toward reconciling the model with the ACT bounds on the CMB observables. We find that attempts to increase n_s through bending lead to negative values of α_s. Those values are disfavored by the ACT bounds just above 2σ even for PBHs in the asteroid-mass range, while the tension becomes stronger for heavier PBHs.

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