Loop Blow-up Inflation: An Overview

Abstract

This proceedings contribution provides an overview of Loop Blow-up Inflation and updates its observational predictions and their comparison with the latest CMB and BAO data. It is based on work originally published in arXiv:2403.04831, done in collaboration with L. Brunelli, M. Cicoli, A. Hebecker, and R. Kuespert, and presented at the 2025 Workshop on Quantum Gravity and Strings. We focus on string loop corrections to the Kähler potential, long regarded as a potential threat to blow-up inflation in the Large Volume Scenario. We argue that these corrections, previously assumed avoidable, are generically present and qualitatively alter the original non-perturbative picture: they invalidate slow-roll near the minimum and instead generate a new slow-roll regime at larger field values, where the scalar potential transitions from an exponential to a power-law plateau. This leads to modified inflationary dynamics and distinct cosmological predictions, including an increased tensor-to-scalar ratio. For the scenario with vanishing extra dark radiation, we compare with the latest combined analyses of ACT, DESI, SPT, BICEP/Keck, and Planck, while for scenarios with non-zero extra dark radiation we use ACT DR6 constraints. Tighter observational bounds on extra dark radiation require updated model parameters in one scenario, yielding revised predictions presented here for the first time. All predictions remain consistent with recent observations, with the ACT+DESI combination yielding near-perfect agreement in the spectral index for vanishing extra dark radiation, with a deviation of $0.03\sigma$. We also comment on subleading loop corrections, which improve robustness by reducing the field value required for slow roll. These results highlight that string loop effects, rather than being merely detrimental, can play a constructive role in realising viable inflation in string compactifications.

15 pages, 2 figures. Contribution to Proceedings of Science (PoS): Corfu Summer Institute 2025 - Workshop on Quantum Gravity and Strings; v2: minor improvements in a few explanations