Effective action of 6D F-Theory with U(1) factors: Rational sections make Chern-Simons terms jump
Thomas W. Grimm, Andreas Kapfer, Jan Keitel
TL;DR
This work develops a comprehensive framework to obtain the $6D$ $(1,0)$ F-theory action with Abelian and non-Abelian factors by leveraging M-theory on a resolved CY$_3$ and a circle-reduced 6D theory. One-loop Chern–Simons terms arising from integrating out massive Coulomb-branch and KK modes reveal the charged spectrum and anomaly structure, with the extended relative Mori cone and non-holomorphic zero sections playing crucial roles in the F-theory limit. The authors demonstrate precise matches between 5D CS data and 6D anomalies for several explicit CY$_3$ examples, thereby determining the full charged matter content and confirming anomaly cancellation. Their approach links geometry—via the Mordell–Weil group, Shioda maps, and Mori cones—to low-energy couplings, providing a powerful diagnostic for consistent F-theory compactifications with $U(1)$ factors and highlighting how KK states can affect CS levels when the zero section is non-holomorphic.
Abstract
We derive the six-dimensional (1,0) effective action arising from F-theory on an elliptically fibered Calabi-Yau threefold with multiple sections. The considered theories admit both non-Abelian and Abelian gauge symmetries. Our derivation employs the M-theory to F-theory duality in five-dimensions after circle reduction. Five-dimensional gauge and gravitational Chern-Simons terms are shown to arise at one-loop by integrating out massive Coulomb branch and Kaluza-Klein modes. In the presence of a non-holomorphic zero section, we find an improved systematic for performing the F-theory limit by using the concept of the extended relative Mori cone. In this situation Kaluza-Klein modes can become lighter than Coulomb branch modes and a jump in the Chern-Simons levels occurs. By determining Chern-Simons terms for various threefold examples we are able to compute the complete six-dimensional charged matter spectrum and show consistency with six-dimensional anomalies.
