Doubled strings, negative strings and null waves

TL;DR

This paper explores the doubled formalism in string theory, analyzing wave solutions, dualities, and exotic string configurations, including negative strings and theories with Euclidean worldsheets, to deepen understanding of string dualities and exotic branes.

Contribution

It introduces a refined doubled formalism for string solutions, including negative strings and Euclidean worldsheet theories, expanding the understanding of dualities and exotic string configurations.

Findings

The wave-like solution in DFT corresponds to the F1/pp-wave duality.

A doubled string can be viewed as static with a dual-oriented configuration.

A new variant of DFT describes theories with Euclidean worldsheets and changing signatures.

Abstract

We revisit the fundamental string (F1) solution in the doubled formalism. We show that the wave-like solution of double field theory (DFT) corresponding to the F1/pp-wave duality pair is more properly a solution of the DFT action coupled to a doubled sigma model action. The doubled string configuration which sources the pp-wave can be thought of as static gauge with the string oriented in a dual direction. We also discuss the DFT solution corresponding to a vibrating string, carrying both winding and momentum. We further show that the solution dual to the F1 in both time and space can be viewed as a "negative string" solution. Negative branes are closely connected to certain exotic string theories which involve unusual signatures for both spacetime and brane worldvolumes. In order to better understand this from the doubled point of view, we construct a variant of DFT suitable for describing theories in which the fundamental string has a Euclidean worldsheet, for which T-dualities appear to change the spacetime signature.