strings@iafe
String Theory Group at Instituto de Astronomía y Física del Espacio, Buenos Aires, Argentina
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.
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.
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.
