Looking for structure in the cobordism conjecture

TL;DR

This paper explores the mathematical and physical aspects of the cobordism conjecture in quantum gravity, proposing new structures and implications for topological and geometric features, including defects and dualities.

Contribution

It introduces the Whitehead tower as a framework for organizing cobordism structures and discusses incorporating geometric data and defects into the conjecture.

Findings

Whitehead tower provides a new organizing principle.

Inclusion of geometric structures like higher U(1)-bundles is feasible.

The conjecture predicts Kaluza--Klein monopoles and relates to T-duality.

Abstract

The cobordism conjecture of the swampland program states that the bordism group of quantum gravity must be trivial. We investigate this statement in several directions, on both the mathematical and physical side. We consider the Whitehead tower construction as a possible organising principle for the topological structures entering the formulation of the conjecture. We discuss why and how to include geometric structures in bordism groups, such as higher U(1)-bundles with connection. The inclusion of magnetic defects is also addressed in some detail. We further elaborate on how the conjecture could predict Kaluza--Klein monopoles, and we study the gravity decoupling limit in the cobordism conjecture, with a few observations on NSNS string backgrounds. We end with comments in relation to T-duality, as well as the finiteness conjecture.