Spectator axions in string inflation and primordial black holes
4 affiliations
- 1Università di Bologna
- 2INFN, Sezione di Bologna
- 3University of Manitoba
- 4University of Winnipeg
Abstract
A bstract : We study the impact of light spectator axions on the seeding of primordial black holes (PBHs) during inflation in string theory. Primordial black holes exhibit unique and novel phenomenology, and may constitute the observed dark matter. Cosmic inflation provides a mechanism for producing them, but such inflation models typically feature Planckian field excursions, necessitating an ultraviolet completion into quantum gravity. String theory provides a natural framework for doing so, and indeed Fibre Inflation has been shown to produce PBHs while satisfying constraints from cosmic microwave background data. In this work we study the dynamics of axions during Fibre Inflation, and find a diverse and rich set of possibilities, including turns in field space and enhancement of primordial perturbations. We find that across most of parameter space, notably an axion with a far sub-Planckian decay constant f ≪ M Pl , there is a negligible impact on the power spectrum of curvature perturbations, indicating an overall robustness of the model. On the other hand, an axion with a larger but still sub-Planckian decay constant, f ≳ 𝒪(0 . 1) M Pl , and an exponentially small prefactor of its non-perturbative potential, can enhance the growth of perturbations, making it easier to achieve the amplification needed to seed PBHs, effectively realizing axion-assisted PBHs in string theory.
Versions
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BibTeX
@article{cicoli2026spectator,
title = {{Spectator axions in string inflation and primordial black holes}},
author = {Michele Cicoli and Dario L. Lorenzoni and Evan McDonough and Francisco G. Pedro},
journal = {Journal of High Energy Physics},
year = {2026},
month = oct,
doi = {10.1007/jhep10(2026)195},
url = {https://link.springer.com/article/10.1007/JHEP10(2026)195},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Spectator axions in string inflation and primordial black holes
AU - Michele Cicoli
AU - Dario L. Lorenzoni
AU - Evan McDonough
AU - Francisco G. Pedro
PY - 2026
DA - 2026/10/19
JO - Journal of High Energy Physics
DO - 10.1007/jhep10(2026)195
UR - https://link.springer.com/article/10.1007/JHEP10(2026)195
AB - A bstract : We study the impact of light spectator axions on the seeding of primordial black holes (PBHs) during inflation in string theory. Primordial black holes exhibit unique and novel phenomenology, and may constitute the observed dark matter. Cosmic inflation provides a mechanism for producing them, but such inflation models typically feature Planckian field excursions, necessitating an ultraviolet completion into quantum gravity. String theory provides a natural framework for doing so, and indeed Fibre Inflation has been shown to produce PBHs while satisfying constraints from cosmic microwave background data. In this work we study the dynamics of axions during Fibre Inflation, and find a diverse and rich set of possibilities, including turns in field space and enhancement of primordial perturbations. We find that across most of parameter space, notably an axion with a far sub-Planckian decay constant f ≪ M Pl , there is a negligible impact on the power spectrum of curvature perturbations, indicating an overall robustness of the model. On the other hand, an axion with a larger but still sub-Planckian decay constant, f ≳ 𝒪(0 . 1) M Pl , and an exponentially small prefactor of its non-perturbative potential, can enhance the growth of perturbations, making it easier to achieve the amplification needed to seed PBHs, effectively realizing axion-assisted PBHs in string theory.
SN - 1029-8479
ER -