strings@iafe
String Theory Group at Instituto de Astronomía y Física del Espacio, Buenos Aires, Argentina
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 α′ 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 α′ 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
I will analyse different 4D STU-models admitting an embedding into N=4 or N=8 gauged supergravity containing (non-)geometric fluxes while still solving the section condition and discuss their ten- or eleven-dimensional uplift. In all cases studied so far all models which can be judged as locally geometric backgrounds from a toroidal viewpoint turn out to have a globally geometric interpretation as type II string theory or M-theory on compact spaces with non-toroidal topology. The seminar will be based on arXiv:1501.03944 and some preliminary results of our work in progress.
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 α'-Corrections to Heterotic Double Field Theory
Kanghoon Lee
We investigate α′-corrections of heterotic double field theory up to quadratic order in the language of supersymmetric O(D,D+dim G) gauged double field theory. After introducing double-vielbein formalism with a parametrization which reproduces heterotic supergravity, we show that supersymmetry for heterotic double field theory up to leading order α′-correction is obtained from supersymmetric gauged double field theory. We discuss the necessary modifications of the symmetries defined in supersymmetric gauged double field theory. Further, we construct supersymmetric completion at quadratic order in α′.
http://arxiv.org/abs/1504.00149
JOURNAL CLUB
22/04/15, 15H
Speaker: Carmen Nuñez.
Star products on graded manifolds and α′-corrections to Courant algebroids from string theory
Andreas Deser
Deformation theory refers to an apparatus in many parts of math and physics for going from an infinitesimal (=first order) deformation to a full deformation, either formal or convergent appropriately. If the algebra being deformed is that of observables, the result is deformation quantization, independent of any realization in terms of Hilbert space operators. There are very important but rare cases in which a formula for a full deformation is known. For physics, the most important is the Moyal-Weyl star product formula. In this paper, we concentrate on deformations of Courant algebroid structures via star products on graded manifolds. In particular, we construct a graded version of the Moyal-Weyl star product. Recently, in Double Field Theory (DFT), deformations of the C-bracket ...
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 α′-corrections
Diego Marques and Carmen Nunez
We construct an O(d,d) invariant universal formulation of the first-order α′-corrections of the string effective actions involving the dilaton, metric and two-form fields. Two free parameters interpolate between four-derivative terms that are even and odd with respect to a Z2-parity transformation that changes the sign of the two-form field. The Z2-symmetric model reproduces the closed bosonic string, and the heterotic string effective action is obtained through a Z2-parity-breaking choice of parameters. The theory is an extension of the generalized frame formulation of Double Field Theory, in which the gauge transformations are deformed by a first-order generalized Green-Schwarz transformation. This deformation defines a duality covariant gauge principle that requires and fixes the four-derivative terms. We discuss the O(d,d) structure of the theory and the (non-)covariance of the required field redefinitions.
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 α′-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 α′ and to all orders in fields, the deformed gauge transformations are Green-Schwarz-deformed diffeomorphisms. We also prove that to first order in α′ 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