# Decoupling Supergravity from the Superstring

## TL;DR

This paper investigates the possibility of deriving pure supergravity theories from string theory in various dimensions, concluding that in dimensions greater than three, additional states prevent a clean decoupling, implying certain supergravity theories may lie in the Swampland.

## Contribution

It demonstrates the limitations of decoupling supergravity from string theory in higher dimensions and proposes that pure N=8 supergravity in four dimensions may not be consistent with string theory.

## Key findings

- Decoupling is possible in 2 and 3 dimensions with only massless states.
- In dimensions > 3, infinite towers of states prevent decoupling.
- Pure N=8 supergravity in 4D likely belongs to the Swampland.

## Abstract

We consider the conditions necessary for obtaining perturbative maximal supergravity in d dimensions as a decoupling limit of type II superstring theory compactified on a (10 -- d)-torus. For dimensions d = 2 and d = 3 it is possible to define a limit in which the only finite-mass states are the 256 massless states of maximal supergravity. However, in dimensions d > 3 there are infinite towers of additional massless and finite-mass states. These correspond to Kaluza--Klein charges, wound strings, Kaluza--Klein monopoles or branes wrapping around cycles of the toroidal extra dimensions. We conclude that perturbative supergravity cannot be decoupled from string theory in dimensions d > 3. In particular, we conjecture that pure N = 8 supergravity in four dimensions is in the Swampland.