Emergent Strings, Duality and Weak Coupling Limits for Two-Form Fields

TL;DR

This paper investigates weak coupling limits for 2-form fields in string theory compactifications, revealing how tensionless strings and dualities manifest in various limits and dimensions, supporting ideas of emergence and the Swampland conjectures.

Contribution

It systematically analyzes weak coupling limits for 2-forms in string compactifications, elucidating the emergence of tensionless strings and dualities across different theories and dimensions.

Findings

Weak coupling limits correspond to infinite-distance limits in moduli space.

Tensionless strings in these limits are dual to fundamental strings in different frames.

M-theory limits lead to emergent extra dimensions rather than tensionless strings.

Abstract

We systematically analyse weak coupling limits for 2-form tensor fields in the presence of gravity. Such limits are significant for testing various versions of the Weak Gravity and Swampland Distance Conjectures, and more broadly, the phenomenon of emergence. The weak coupling limits for 2-forms correspond to certain infinite-distance limits in the moduli space of string compactifications, where asymptotically tensionless, solitonic strings arise. These strings are identified as weakly coupled fundamental strings in a dual frame, which makes the idea of emergence manifest. Concretely we first consider weakly coupled tensor fields in six-dimensional compactifications of F-theory, where the arising tensionless strings play the role of dual weakly coupled heterotic strings. As the main part of this work, we consider certain infinite distance limits of Type IIB strings on K3 surfaces, for which we show that the asymptotically tensionless strings describe dual fundamental Type IIB strings, again on K3 surfaces. By contrast the analogous weak coupling limits of M-theory compactifications are found to correspond to an F-theory limit where an extra dimension emerges rather than tensionless strings. We comment on extensions of our findings to four-dimensional compactifications.