The Weak Gravity Conjecture and Effective Field Theory

TL;DR

This paper examines the Weak Gravity Conjecture (WGC), demonstrating models that satisfy it but produce low-energy EFTs violating it, and proposes a weaker, entropy-bound-based constraint on EFT cutoff scales.

Contribution

It reveals loopholes in the WGC through Higgsing models and suggests a weaker, entropy-based bound on EFT validity, challenging the conjecture's universality.

Findings

Models satisfying WGC can produce EFTs that violate it after Higgsing.

Magnetic monopole arguments are evaded in Higgs phases due to magnetic confinement.

A weaker cutoff bound for EFTs is proposed based on entropy considerations.

Abstract

The Weak Gravity Conjecture (WGC) is a proposed constraint on theories with gauge fields and gravity, requiring the existence of light charged particles and/or imposing an upper bound on the field theory cutoff $\Lambda$. If taken as a consistency requirement for effective field theories (EFTs), it rules out possibilities for model-building including some models of inflation. I demonstrate simple models which satisfy all forms of the WGC, but which through Higgsing of the original gauge fields produce low-energy EFTs with gauge forces that badly violate the WGC. These models illustrate specific loopholes in arguments that motivate the WGC from a bottom-up perspective; for example the arguments based on magnetic monopoles are evaded when the magnetic confinement that occurs in a Higgs phase is accounted for. This indicates that the WGC should not be taken as a veto on EFTs, even if it turns out to be a robust property of UV quantum gravity theories. However, if the latter is true then parametric violation of the WGC at low energy comes at the cost of non-minimal field content in the UV. I propose that only a very weak constraint is applicable to EFTs, $\Lambda \lesssim \left(-\log g \right)^{-1/2} M_\text{pl}$ where $g$ is the gauge coupling, motivated by entropy bounds. Remarkably, EFTs produced by Higgsing a theory that satisfies the WGC can saturate but not violate this bound.