A Geometry for Non-Geometric String Backgrounds

A geometric string solution has background fields in overlapping coordinate patches related by diffeomorphisms and gauge transformations, while for a non-geometric background this is generalised to allow transition functions involving duality transformations. Non-geometric string backgrounds arise from T-duals and mirrors of flux compactifications, from reductions with duality twists and from asymmetric orbifolds. Strings in ` T-fold' backgrounds with a local $n$-torus fibration and T-duality transition functions in $O(n,n;\Z)$ are formulated in an enlarged space with a $T^{2n}$ fibration which is geometric, with spacetime emerging locally from a choice of a $T^n$ submanifold of each $T^{2n}$ fibre, so that it is a subspace or brane embedded in the enlarged space. T-duality acts by changing to a different $T^n$ subspace of $T^{2n}$. For a geometric background, the local choices of $T^n$ fit together to give a spacetime which is a $T^n$ bundle, while for non-geometric string backgrounds they do not fit together to form a manifold. In such cases spacetime geometry only makes sense locally, and the global structure involves the doubled geometry. For open strings, generalised D-branes wrap a $T^n$ subspace of each $T^{2n}$ fibre and the physical D-brane is the part of the part of the physical space lying in the generalised D-brane subspace.Comment: 28 Pages. Minor change

Algebraic structures in exceptional geometry

Exceptional field theory (EFT) gives a geometric underpinning of the U-duality symmetries of M-theory. In this talk I give an overview of the surprisingly rich algebraic structures which naturally appear in the context of EFT. This includes Borcherds superalgebras, Cartan type superalgebras (tensor hierarchy algebras) and L∞ algebras. This is the written version of a talk based mainly on refs. [1-6], presented at ISQS25, Prague, June 2017, at QTS-10/LT-12, Varna, June 2017, at SQS 2017, Dubna, Aug. 2017, and at the 9th Mathematical Physics Meeting, Belgrade, Sept. 2017

Algebraic Structures in Extended Geometry

Extended geometry is a unifying framework including exceptional field theory (XFT) and double field theory (DFT). It gives a geometric underpinning of the duality symmetries of M-theory. In this talk I give an overview of the surprisingly rich algebraic structures which naturally appear in the context of extended geometry. This includes Borcherds superalgebras, Cartan type superalgebras (tensor hierarchy algebras) and L-infinity algebras. This is the written version of a talk based mainly on [1-6], presented at SQS 2017, Dubna, Aug. 2017