top of page

SEMINARS 2015​

JOURNAL CLUB

 

05/01/15, 16H

 

Speaker: Diego Marques

 

Heterotic Effective Action and Duality Symmetries Revisited

Olaf Hohm, Ashoke Sen, Barton Zwiebach

The dimensional reduction of heterotic supergravity with gauge fields truncated to the Cartan subalgebra exhibits a continuous O(d,d+16;R) global symmetry, related to the O(d,d+16;Z) T-duality of heterotic strings on a d-torus. The O(d,d+16;R) symmetry is not present, however, if the supergravity reduction is done including the full set of E_8 x E_8 or SO(32) gauge fields. We analyze which duality symmetries are realized to all orders in Î±â€² in the proper effective field theories for the massless string states. We find a universal O(d,d;R) symmetry, also predicted by double field theory. We confirm this by giving a novel formulation of the dimensionally reduced supergravity in terms of O(d,d) multiplets, and we discuss cases of symmetry enhancement.

 

http://arxiv.org/abs/1411.5696

 

JOURNAL CLUB

 

07/09/15, 14H

 

Speaker: Diego Marques

 

Double Field Theory on Group Manifolds

Ralph Blumenhagen, Falk Hassler, Dieter Lust

A new version of double field theory (DFT) is derived for the exactly solvable background of an in general left-right asymmetric WZW model in the large level limit. This generalizes the original DFT that was derived via expanding closed string field theory on a torus up to cubic order. The action and gauge transformations are derived for fluctuations around the generalized group manifold background up to cubic order, revealing the appearance of a generalized Lie derivative and a corresponding C-bracket upon invoking a new version of the strong constraint. In all these quantities a background dependent covariant derivative appears reducing to the partial derivative for a toroidal background. This approach sheds some new light on the conceptual status of DFT, its background (in-)dependence and the up-lift of non-geometric Scherk-Schwarz reductions.

 

http://arxiv.org/abs/1410.6374

 

JOURNAL CLUB

 

14/09/15, 14H

 

Speaker: Alejandro Cabo

 

T-duality Constraints on Higher Derivatives Revisited

Olaf Hohm, Barton Zwiebach

We ask to what extent are the higher-derivative corrections of string theory constrained by T-duality. The seminal early work by Meissner tests T-duality by reduction to one dimension using a distinguished choice of field variables in which the bosonic string action takes a Gauss-Bonnet-type form. By analyzing all field redefinitions that may or may not be duality covariant and may or may not be gauge covariant we extend the procedure to test T-duality starting from an action expressed in arbitrary field variables. We illustrate the method by showing that it determines uniquely the first-order Î±â€² corrections of the bosonic string, up to terms that vanish in one dimension. We also use the method to glean information about the O(α′2) corrections in the double field theory with Green-Schwarz deformation.

 

http://arxiv.org/abs/1510.00005

 

JOURNAL CLUB

 

21/10/15, 14H

 

Speaker: Sergio Iguri

 

Critical Dimension of String Theories in Curved Space

Dennis Nemeschansky, S. Yankielowicz

The critical dimension of string theories in which the background metric is a product of Minkowski space and an SU(N) or SO(N) group manifold is derived. A consistent string theory can be constructed only in the presence of a Wess-Zumino term associated with the compactified dimension. This implies that the compactified radius is quantized in units of the string tension. A generalization to the supersymmetric case is discussed.

 

http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.54.620

JOURNAL CLUB

 

23/10/15, 14:30H

 

Speaker: J. Anibal Sierra-Garcia

 

Non-Abelian T-duality

SEMINAR

 

25/02/15, 14H

Aula Chica.

 

Speaker: Jose Juan Fernandez-Melgarejo.

 

Twistings, susy and the section condition.

 

SEMINAR

 

04/03/15, 14H

 

Speaker: Giuseppe Dibitetto.

 

Geometric Non-Geometry

 

 

http://arxiv.org/abs/1501.03944

 

JOURNAL CLUB

 

08/04/15, 14H

Aula Chica.

 

Speaker: Alejandro Rosabal.

 

On winding gauge enhancement in double/generalized geometry.

 

JOURNAL CLUB

 

15/04/15, 15H

 

Speaker: Diego Marqués.

 

Quadratic Î±'-Corrections to Heterotic Double Field Theory

Kanghoon Lee

 

 

http://arxiv.org/abs/1504.00149

 

JOURNAL CLUB

 

22/04/15, 15H

 

Speaker: Carmen Nuñez.

 

Star products on graded manifolds and Î±â€²-corrections to Courant algebroids from string theory

Andreas Deser

 

 

http://arxiv.org/abs/1412.5966

SEMINAR

 

13/07/15, 14H

 

Speaker: Alejandro Rosabal.

 

More on winding gauge enhancement in DFT

 

SEMINAR

 

14/07/15, 14H

 

Speaker: Diego Marques.

 

T-duality and Î±â€²-corrections

Diego Marques and Carmen Nunez

 

 

http://arxiv.org/abs/1507.00652

JOURNAL CLUB

 

08/09/15, 14H

 

Speaker: Yago Cagnacci

 

Relating Double Field Theory to the Scalar Potential of N=2 Gauged Supergravity

Ralph Blumenhagen, Anamaria Font, Erik Plauschinn

The double field theory action in the flux formulation is dimensionally reduced on a Calabi-Yau three-fold equipped with non-vanishing type IIB geometric and non-geometric fluxes. First, we rewrite the metric-dependent reduced DFT action in terms of quantities that can be evaluated without explicitly knowing the metric on the Calabi-Yau manifold. Second, using properties of special geometry we obtain the scalar potential of N=2 gauged supergravity. After an orientifold projection, this potential is consistent with the scalar potential arising from the flux-induced superpotential, plus an additional D-term contribution.

 

http://arxiv.org/abs/1507.08059

 

JOURNAL CLUB

 

22/09/15, 14H

 

Speaker: Carmen Nuñez

 

Canonical formulation and conserved charges of double field theory

Usman Naseer

We provide the canonical formulation of double field theory. It is shown that this dynamics is subject to primary and secondary constraints. The Poisson bracket algebra of secondary constraints is shown to close on-shell according to the C-bracket. A systematic way of writing boundary integrals in doubled geometry is given. By including appropriate boundary terms in the double field theory Hamiltonian, expressions for conserved energy and momentum of an asymptotically flat doubled space-time are obtained and applied to a number of solutions.

 

http://arxiv.org/abs/1508.00844

 

JOURNAL CLUB

 

30/09/15, 14H

 

Speaker: Eric Lescano

 

Double Metric, Generalized Metric and Î±â€²-Geometry

Olaf Hohm, Barton Zwiebach

We relate the unconstrained `double metric' of the `α′-geometry' formulation of double field theory to the constrained generalized metric encoding the spacetime metric and b-field. This is achieved by integrating out auxiliary field components of the double metric in an iterative procedure that induces an infinite number of higher-derivative corrections. As an application we prove that, to first order in Î±â€² and to all orders in fields, the deformed gauge transformations are Green-Schwarz-deformed diffeomorphisms. We also prove that to first order in Î±â€² the spacetime action encodes precisely the Green-Schwarz deformation with Chern-Simons forms based on the torsionless gravitational connection. This seems to be in tension with suggestions in the literature that T-duality requires a torsionful connection, but we explain that these assertions are ambiguous since actions that use different connections are related by field redefinitions.

 

http://arxiv.org/abs/1509.02930

 

SEMINAR

 

25/11/15, 14H, IAFE

 

Speaker: Jorge Russo

 

Dualidades de supercuerdas y teorias de supergravedad

bottom of page