# Swampland Bounds on the Abelian Gauge Sector

## TL;DR

This paper establishes universal bounds on the number of abelian gauge factors in six-dimensional supergravity theories and F-theory models, based on consistency conditions of BPS strings and unitarity constraints, extending to four-dimensional vacua.

## Contribution

It derives new bounds on abelian gauge group factors in 6D supergravity and F-theory, linking string consistency to geometric properties of Calabi-Yau manifolds.

## Key findings

- Bound N ≤ 20 (or 22) for theories with tensors and matter.
- Bound N ≤ 16 for F-theory realizations with unitarity constraints.
- Universal bounds on Mordell-Weil rank of elliptic Calabi-Yau threefolds.

## Abstract

We derive bounds on the number of abelian gauge group factors in six-dimensional gravitational theories with minimal supersymmetry and in their F-theoretic realisations. These bounds follow by requiring consistency of certain BPS strings in the spectrum of the theory, as recently proposed in the literature. Under certain assumptions this approach constrains the number of abelian gauge group factors in six-dimensional supergravity theories with at least one tensor multiplet to be $N \leq 20$ (or $N \leq 22$ in absence of charged matter). For any geometric F-theory realisation with at least one tensor multiplet we establish the bound $N \leq 16$ by demanding unitarity of a heterotic solitonic string which exists even in absence of a perturbative heterotic dual. This result extends to four-dimensional F-theory vacua on any blowup of a rational fibration. Our findings lead to universal bounds on the rank of the Mordell-Weil group of elliptically fibered Calabi-Yau threefolds.