When Rational Sections Become Cyclic: Gauge Enhancement in F-theory via Mordell--Weil Torsion

TL;DR

This paper investigates how complex structure deformations in F-theory can lead to gauge enhancements involving non-simply-connected groups through Mordell--Weil torsion, specifically focusing on Z2 torsion cases.

Contribution

It constructs explicit F-theory models with Z2 Mordell--Weil torsion, revealing new gauge groups and analyzing their geometric and spectral properties.

Findings

Constructed generic solutions with Z2 torsion in elliptic fibrations.

Identified gauge groups [SU(2) x SU(4)]/Z2 x SU(2) and related subgroups.

Revealed conceptual puzzles in spectrum analysis on genus-one fibrations.

Abstract

We explore novel gauge enhancements from abelian to non-simply-connected gauge groups in F-theory. To this end we consider complex structure deformations of elliptic fibrations with a Mordell--Weil group of rank one and identify the conditions under which the generating section becomes torsional. For the specific case of Z2 torsion we construct the generic solution to these conditions and show that the associated F-theory compactification exhibits the global gauge group [SU(2) x SU(4)]/Z2 x SU(2). The subsolution with gauge group SU(2)/Z2 x SU(2), for which we provide a global resolution, is related by a further complex structure deformation to a genus-one fibration with a bisection whose Jacobian has a Z2 torsional section. While an analysis of the spectrum on the Jacobian fibration reveals an SU(2)/Z2 x Z2 gauge theory, reproducing this result from the bisection geometry raises some conceptual puzzles about F-theory on genus-one fibrations.