# The Swampland Distance Conjecture and Towers of Tensionless Branes

## TL;DR

This paper explores how infinite distance limits in Calabi-Yau compactifications lead to towers of tensionless particles, strings, and domain walls, affecting effective field theories and consistent with mirror symmetry.

## Contribution

It demonstrates that in 4d type IIA/IIB Calabi-Yau compactifications, not only particles but also domain walls and strings become tensionless at infinite moduli distance, extending the Swampland Distance Conjecture.

## Key findings

- Towers of tensionless domain walls and strings appear alongside particles.
- These towers can occur at the same scale as the string or Kaluza-Klein scales.
- The structure of towers is consistent with mirror symmetry and involves exotic non-geometric fluxes.

## Abstract

The Swampland Distance Conjecture states that at infinite distance in the scalar moduli space an infinite tower of particles become exponentially massless. We study this issue in the context of 4d type IIA and type IIB Calabi-Yau compactifications. We find that for large moduli not only towers of particles but also domain walls and strings become tensionless. We study in detail the case of type IIA and IIB ${\cal N}=1$ CY orientifolds and show how for infinite K\"ahler and/or complex structure moduli towers of domain walls and strings become tensionless, depending on the particular direction in moduli space. For the type IIA case we construct the monodromy orbits of domain walls in detail. We study the structure of mass scales in these limits and find that these towers may occur at the same scale as the fundamental string scale or the KK scale making sometimes difficult an effective field theory description. The structure of IIA and IIB towers are consistent with mirror symmetry, as long as towers of exotic domain walls associated to non-geometric fluxes also appear. We briefly discuss the issue of emergence within this context and the possible implications for 4d vacua.