Aspects of the Doubled Worldsheet

Understand

We clarify the relation between various approaches to the manifestly T-duality symmetric string.

• We explain in detail how the PST covariant doubled string arises from an unusual gauge fixing.
• We pay careful attention to the role of "spectator" fields in this process and also show how the T-duality invariant doubled dilaton emerges naturally.
• We extend these ideas to non-Abelian T-duality and show they give rise to the duality invariant formalism based on the semi-Abelian Drinfeld Double.