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SEMINARS 2014​

JOURNAL CLUB

 

26/03/14, 16H

 

Speaker: Carmen Nuñez

 

A Note on the CFT Origin of the Strong Constraint of DFT

Andre Betz, Ralph Blumenhagen, Dieter Lust, Felix Rennecke

In double field theory, motivated by its field theoretic consistency, the level matching condition is generalized to the so-called strong constraint. In this note, it is investigated what the two-dimensional conformal field theory origin of this constraint is. Initially treating the left- and right-movers as independent, we compute the torus partition function as well as a generalized Virasoro-Shapiro amplitude. In non-compact directions the strong constraint arises from the factorization of the Virasoro-Shapiro amplitude over physical states as determined by the modular invariant partition function. From the same argument, along internal toroidal directions, no analogous constraint arises.

 

http://arxiv.org/abs/arXiv:1402.1686

 

SEMINAR

 

06/05/14 - 14H - Aula chica

 

Speaker: David Berman

 

Global aspects of double geometry + Strings and branes are waves

 

http://arxiv.org/abs/arXiv:1401.1311

 

http://arxiv.org/abs/arXiv:1403.7198

 

 

 

 

JOURNAL CLUB

 

22/05/14 - 14H - Aula chica

 

Speaker: Jose Juan Fernandez-Melgarejo

 

A discussion on the Lee-Park double sigma model

 

http://arxiv.org/abs/arXiv:1307.8377

 

 

JOURNAL CLUB

 

26/05/14 - 14H - Aula chica

 

Speaker: Sergio Iguri

Bialgebras, Loday and Leibniz algebras, and their relation with generalized geometry and double field theory.

 

 

 

JOURNAL CLUB

 

05/06/14 - 15H - Aula chica

 

Speaker: Carmen Nuñez

 

Non-commutativity and non-associativity of the doubled string in non-geometric backgrounds

Chris D. A. Blair

 

We use a T-duality invariant action to investigate the behaviour of a string in non-geometric backgrounds, where there is a non-trivial global O(D,D) patching or monodromy. This action leads to a set of Dirac brackets describing the dynamics of the doubled string, with these brackets determined only by the monodromy. This allows for a simple derivation of non-commutativity and non-associativity in backgrounds which are (even locally) non-geometric. We focus here on the example of the three-torus with H-flux, and also comment on the relation to the exotic 522 brane, which shares the same monodromy.

 

http://arxiv.org/abs/arXiv:1405.2283

 

 

JOURNAL CLUB

 

11/04/14 - 14H

 

Speaker: Alejandro Rosabal

 

Spheres, generalised parallelisability and consistent truncations

Kanghoon Lee, Charles Strickland-Constable, Daniel Waldram

We show that generalised geometry gives a unified description of maximally supersymmetric consistent truncations of ten- and eleven-dimensional supergravity. In all cases the reduction manifold admits a "generalised parallelisation" with a frame algebra with constant coefficients. The consistent truncation then arises as a generalised version of a conventional Scherk-Schwarz reduction with the frame algebra encoding the embedding tensor of the reduced theory. The key new result is that all round-sphere Sd geometries admit such generalised parallelisations with an SO(d+1) frame algebra. Thus we show that the remarkable consistent truncations on S3, S4, S5 and S7 are in fact simply generalised Scherk-Schwarz reductions. This description leads directly to the standard non-linear scalar-field ansatze and as an application we give the full scalar-field ansatz for the type IIB truncation on S5.

 

http://arxiv.org/abs/arXiv:1401.3360

JOURNAL CLUB

 

24/04/14 - 14H - Aula Chica

 

Speaker: Victor Penas

 

The D-brane U-scan

Eric A. Bergshoeff and Fabio Riccioni

We consider the D-branes that occur in IIA/IIB string theory compactified on a torus. We review how a general expression for the Wess-Zumino term of such branes is derived. We also review the method to determine the D-brane Wess-Zumino term in a U-duality covariant way, and we apply it to derive all the branes obtained by transforming the D-branes under U-duality in any dimension above five. We finally determine all the supersymmetric branes supporting worldvolume tensor multiplets that occur in these theories in any dimension.

 

http://arxiv.org/abs/arXiv:1109.1725

JOURNAL CLUB

 

29/04/14 - 14H - Aula chica

 

Speaker: Diego Marques

 

Review on large gauge transformations in DFT

 

http://arxiv.org/abs/arXiv:1207.4198

 

http://arxiv.org/abs/arXiv:1304.5946

 

http://arxiv.org/abs/arXiv:1401.1311

 

JOURNAL CLUB

 

19/06/14 - 14H - Aula chica

 

Speaker: Diego Marques

 

Generalised Space-time and Gauge Transformations

Peter West

 

We consider the generalised space-time introduced by the author in 2003 in the context of the non-linear realisation of the semi-direct product of E11 and its first fundamental representation. For all the fields we propose gauge transformations which are compatible with the underlying E11 structure. A crucial role is played by the generalised vielbein that the generalised space-time possess. We work out the explicit form of the gauge transformations, at low levels, in four, five and eleven dimensions.

 

 

http://arxiv.org/abs/arXiv:1403.6395

 

 

JOURNAL CLUB

 

26/06/14 - 15H - Aula chica

 

Speaker: Alejandro Rosabal

 

Exceptional Field Theory III: E8(8)

Olaf Hohm, Henning Samtleben

 

We develop exceptional field theory for E8(8), defined on a (3+248)-dimensional generalized spacetime with extended coordinates in the adjoint representation of E8(8). The fields transform under E8(8) generalized diffeomorphisms and are subject to covariant section constraints. The bosonic fields include an `internal' dreibein and an E8(8)-valued `zweihundertachtundvierzigbein' (248-bein)...

 

http://arxiv.org/abs/arXiv:1406.3348

 

 

JOURNAL CLUB

 

03/07/14 - 15H - Aula chica

 

Speaker: Jose Juan Fernandez-Melgarejo

 

Finite Gauge Transformations and Geometry in Double Field Theory

Chris Hull

 

Recently proposed forms for gauge transformations with finite parameters in double field theory are discussed and problematic issues are identified. A new form for finite gauge transformations is derived that reveals the underlying gerbe structure and the close relationship with generalised geometry. The nature of generalised tensors is elucidated, and in particular it is seen that the presence of a constant metric with split signature does not restrict the doubled geometry, provided it is a generalised tensor rather than a conventional tensor.

 

http://arxiv.org/abs/arXiv:1406.7794

 

 

JOURNAL CLUB

 

10/07/14 - 15H - Aula chica

 

Speaker: Diego Marqués

 

Green-Schwarz mechanism and α′-deformed Courant brackets

Olaf Hohm and Barton Zwiebach

 

We establish that the unusual two-form gauge transformations needed in the Green-Schwarz anomaly cancellation mechanism fit naturally into an α′-deformed generalized geometry. The algebra of gauge transformations is a consistent deformation of the Courant bracket and features a nontrivial modification of the diffeomorphism group. This extension of generalized geometry emerged from a `doubled α′-geometry', which provides a construction of exactly gauge and T-duality invariant α′ corrections to the effective action.

 

JOURNAL CLUB

 

24/07/14 - 15H - Aula chica

 

Speaker: Oscar Bedoya

 

Double Field Theory at Order α'

Olaf Hohm and Barton Zwiebach

 

We investigate α′ corrections of bosonic strings in the framework of double field theory. The previously introduced "doubled α′-geometry" gives α′-deformed gauge transformations arising in the Green-Schwarz anomaly cancellation mechanism but does not apply to bosonic strings. These require a different deformation of the duality-covariantized Courant bracket which governs the gauge structure. This is revealed by examining the α′ corrections in the gauge algebra of closed string field theory. We construct a four-derivative cubic double field theory action invariant under the deformed gauge transformations, giving a first glimpse of the gauge principle underlying bosonic string α′ corrections. The usual metric and b-field are related to the duality covariant fields by non-covariant field redefinitions.

 

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