Warm Inflation with the Standard Model from an Axion-Like Particle

by Dr Sebastian Zell (LMU Munich)

Thursday 6 Nov 2025, 11:00 → 12:00 Europe/Amsterdam

Positron room (Nikhef)

Observations strongly indicate that inflation – a period of accelerated expansion – occurred in the first moments of our Universe. Yet the particle physics origin of this phase remains unknown. I will present a scenario in which an axion-like particle, coupled to non-Abelian gauge fields, drives warm inflation – a version of inflation sustained by thermal friction from sphaleron transitions. After an introductory review of inflation and axions, I will show why a standard axion cannot cause inflation and explain how light fermions, previously thought to prevent sphaleron heating, are rendered harmless by cosmic expansion. These insights lead to a simple model in which an axion-like particle drives warm inflation solely through its coupling to Standard Model QCD, with potentially observable implications for axion detection experiments.

Based on:
K. Berghaus, M. Drewes, S. Zell, Warm Inflation with the Standard Model, Phys. Rev. Lett. 135 (2025) 17,  arXiv:2503.21740.
S. Zell, No Warm Inflation From a Vanilla Axion, Phys. Rev. D 112 (2025) L081307,  arXiv:2408.0774.
M. Drewes and S. Zell, On Sphaleron Heating in the Presence of Fermions, JCAP 06 (2024) 038, arXiv:2312.13739.