Populating the swampland: the case of U(1)^496 and E_8 x U(1)^248

TL;DR

This paper examines the special U(1)^496 and E_8 x U(1)^248 supergravity theories in 10 dimensions, providing evidence that they may not correspond to consistent quantum gravity theories due to singularity and gauge enhancement issues.

Contribution

It presents new arguments suggesting that these two supergravity theories might not have consistent quantum gravity completions, based on anomaly constraints and singularity analysis.

Findings

Gauge enhancement problematic for these theories upon compactification.

These theories exhibit singularities that are not resolved by known mechanisms.

They may be too Abelian to be consistent quantum gravity theories.

Abstract

For d=10 N=1 SUGRA coupled to d=10 N=1 SYM, anomaly cancellation places severe constraints on the allowed gauge groups. Besides the ones known to appear in string theory, only U(1)^496 and E_8 x U(1)^248 are allowed. There are no known theories of quantum gravity that reduce in some limit to these two last supergravity theories, and in this note I present some evidence that those quantum theories might not exist. The first observation is that, upon compactification, requring that the quantum theory possesses a moduli space with finite volume typically implies the existence of singularities where the 4d gauge group is enhanced, but for these two theories that gauge enhancement is problematic from the 10d point of view. I also point out that while these four supergravity theories present repulson-type singularities, the known mechanism that repairs those singularities for the first two - the non-Abelian enhancon - is not available for the last two theories. In short, these two supergravity theories might be too Abelian for their own good.