The Question

Starting Point

The starting point is a question.

What is the gravitational theory naturally implied by closed string theory?

This question is more precise than the question of whether string theory contains gravity. It does. The massless spectrum of a closed string contains a spin-two field, and its low-energy dynamics includes the Einstein equations in an appropriate limit.

The issue is not existence. The issue is organization.

If closed string theory has its own gravitational content, then one should ask what the corresponding geometry is, what its invariant fields are, what its curvature is, what its field equation is, how matter couples to it, and how it can be tested.

Observation

The universal massless sector of closed string theory is

This is the observation. It is not a conjecture and it is not a matter of interpretation.

The Riemannian metric \(g_{\mu\nu}\) is not alone. It appears together with the two-form gauge field \(B_{\mu\nu}\) and the dilaton \(\phi\). These fields are not optional additions to the closed-string spectrum. They are part of the same universal massless sector.

This observation creates a conceptual tension. General Relativity geometrizes the metric. It does not, by itself, geometrize the complete multiplet \(\{g_{\mu\nu}, B_{\mu\nu}, \phi\}\). Supergravity incorporates the same fields dynamically, but it is usually expressed after a choice of Riemannian variables has already been made.

The scientific problem is therefore not to add more fields to General Relativity. The problem is to understand whether the whole closed-string massless sector is itself gravitational.

Scope of the Program

This research program concerns the gravitational theory implied by the universal massless sector of perturbative closed string theory.

It does not attempt to formulate the geometry of M-theory or of exceptional extensions. Nor does it assume that a Riemannian formulation is the most general description of the closed-string gravitational sector.

Within this scope, Double Field Theory is treated as the working geometric framework to be tested.