An extradimensional axion in a 5D warped orbifold GUT

by Gongjun Choi (University of Minnesota)

Friday 27 Mar 2026, 12:00 → 14:00 America/Chicago

Extra-dimensional axions are particularly compelling due to their exceptional quality. In the context of 5D grand unified theories (GUT) with a flat extra dimension, maintaining perturbative gauge coupling unification can require the axion decay constant to exceed the GUT scale. This arises because the decay constant is tied to the KK scale, while the gauge coupling evolution transitions to power-law running above that threshold. In this talk, we examine whether this conclusion persists in warped 5D grand unified frameworks. We demonstrate that, in contrast to the flat case, an extra-dimensional axion in a warped background can naturally realize a decay constant within the conventional QCD axion window without jeopardizing gauge unification. Finally, we briefly outline a mechanism, developed in ongoing work, for suppressing extradimensional axion isocurvature perturbations, based on the idea of a dynamically evolving axion decay constant in the early universe.

ExtraD Axion_Choi_Mar27.pdf