String Dualities at Order α

We compute the cosmological reduction of the fourth powers of the Riemann tensor claimed to arise in string theory at order α^{'}^{3}, with an overall coefficient proportional to ζ(3), and show that it is compatible with an O(9,9) symmetry. This confirms the general result in string theory, due to Sen [O(d)×O(d) symmetry of the space of cosmological solutions in string theory, scale factor duality and two-dimensional black holes, Phys. Lett. B 271, 295 (1991)PYLBAJ0370-269310.1016/0370-2693(91)90090-D], that classical string theory with d-dimensional translation invariance admits an O(d,d) symmetry to all orders in α^{'}.

Duality Hierarchies and Differential Graded Lie Algebras.

The gauge theories underlying gauged supergravity and exceptional field theory are based on tensor hierarchies: generalizations of Yang-Mills theory utilizing algebraic structures that generalize Lie algebras and, as a consequence, require higher-form gauge fields. Recently, we proposed that the algebraic structure allowing for consistent tensor hierarchies is axiomatized by 'infinity-enhanced Leibniz algebras' defined on graded vector spaces generalizing Leibniz algebras. It was subsequently shown that, upon appending additional vector spaces, this structure can be reinterpreted as a differential graded Lie algebra. We use this observation to streamline the construction of general tensor hierarchies, and we formulate dynamics in terms of a hierarchy of first-order duality relations, including scalar fields with a potential.

Leibniz Gauge Theories and Infinity Structures.

We formulate gauge theories based on Leibniz(-Loday) algebras and uncover their underlying mathematical structure. Various special cases have been developed in the context of gauged supergravity and exceptional field theory. These are based on 'tensor hierarchies', which describe towers of p-form gauge fields transforming under non-abelian gauge symmetries and which have been constructed up to low levels. Here we define 'infinity-enhanced Leibniz algebras' that guarantee the existence of consistent tensor hierarchies to arbitrary level. We contrast these algebras with strongly homotopy Lie algebras ( L ∞ algebras), which can be used to define topological field theories for which all curvatures vanish. Any infinity-enhanced Leibniz algebra carries an associated L ∞ algebra, which we discuss.

Green-Schwarz Mechanism for String Dualities.

We determine the complete spacetime action to first order in α^{'} for the massless fields of bosonic string theory compactified on a d-dimensional torus. A fully systematic procedure is developed that brings the action into a minimal form in which all fields apart from the metric enter only with first-order derivatives. T duality implies that this action must have a global O(d,d,R) symmetry, and we show that this requires a Green-Schwarz type mechanism for α^{'}-deformed O(d,d,R) transformations. In terms of a frame formalism with GL(d)×GL(d) gauge symmetry this amounts to a modification of the three-form curvature by a Chern-Simons term for composite gauge fields.

Background Independence and Duality Invariance in String Theory.

Closed string theory exhibits an O(D,D) duality symmetry on tori, which in double field theory is manifest before compactification. I prove that to first order in α^{'} there is no manifestly background independent and duality invariant formulation of bosonic string theory in terms of a metric, b field, and dilaton. To this end I use O(D,D) invariant second order perturbation theory around flat space to show that the unique background independent candidate expression for the gauge algebra at order α^{'} is inconsistent with the Jacobi identity. A background independent formulation exists instead for frame variables subject to α^{'}-deformed frame transformations (generalized Green-Schwarz transformations). Potential applications for curved backgrounds, as in cosmology, are discussed.

Zwei-dreibein gravity: a two-frame-field model of 3D massive gravity.

We present a generally covariant and parity-invariant two-frame field ("zwei-dreibein") action for gravity in three space-time dimensions that propagates two massive spin-2 modes, unitarily, and we use Hamiltonian methods to confirm the absence of unphysical degrees of freedom. We show how zwei-dreibein gravity unifies previous "3D massive gravity" models and extends them, in the context of the AdS/CFT correspondence, to allow for a positive central charge consistent with bulk unitarity.

Exceptional form of D=11 supergravity.

Eleven-dimensional supergravity reveals large exceptional symmetries upon reduction, in accordance with the U-duality groups of M theory, but their higher-dimensional geometric origin has remained a mystery. In this Letter, we show that D=11 supergravity can be extended to be fully covariant under the exceptional groups E(n(n)), n=6, 7, 8. Motivated by a similar formulation of double field theory we introduce an extended "exceptional spacetime." We illustrate the construction by giving the explicit E(6(6)) covariant form: the full D=11 supergravity, in a 5+6 splitting of coordinates but without truncation, embeds into an E(6(6)) covariant 5+27 dimensional theory. We argue that this covariant form likewise comprises type IIB supergravity.

Geometric action for nongeometric fluxes.

We give a geometrical interpretation of the nongeometric Q and R fluxes. To this end, we consider double field theory in a formulation that is related to the conventional one by a field redefinition taking the form of a T duality inversion. The R flux is a tensor under diffeomorphisms and satisfies a nontrivial Bianchi identity. The Q flux can be viewed as part of a connection that covariantizes the winding derivatives with respect to diffeomorphisms. We give a higher-dimensional action with a kinetic term for the R flux and a "dual" Einstein-Hilbert term containing the connection Q.

Unification of type-II strings and T duality.

We present a unified description of the low-energy limits of type-II string theories. This is achieved by a formulation that doubles the space-time coordinates in order to realize the T-duality group O(10,10) geometrically. The Ramond-Ramond fields are described by a spinor of O(10,10), which couples to the gravitational fields via the Spin(10,10) representative of the so-called generalized metric. This theory, which is supplemented by a T-duality covariant self-duality constraint, unifies the type-II theories in that each of them is obtained for a particular subspace of the doubled space.

Massive gravity in three dimensions.

A particular higher-derivative extension of the Einstein-Hilbert action in three spacetime dimensions is shown to be equivalent at the linearized level to the (unitary) Pauli-Fierz action for a massive spin-2 field. A more general model, which also includes "topologically-massive" gravity as a special case, propagates the two spin-2 helicity states with different masses. We discuss the extension to massive N-extended supergravity, and we present a "cosmological" extension that admits an anti-de Sitter vacuum.