strings@iafe
String Theory Group at Instituto de AstronomÃa y FÃsica del Espacio, Buenos Aires, Argentina
SEMINARS 2018​
JOURNAL CLUB
21/03/18, 14H (Aula Chica)
Speaker: Bernardo Fraiman
A new twist on heterotic string compactifications
Bernardo Fraiman, Mariana Graña, Carmen A. Núñez
​
A rich pattern of gauge symmetries is found in the moduli space of heterotic string toroidal compactifications, at fixed points of the T-duality transformations. We analyze this pattern for generic tori, and scrutinize in full detail compactifications on a circle. We show the gauge symmetry groups that arise at special points, in figures of slices of the 17-dimensional moduli space of Wilson lines and circle radii. We then study the target space realization of the duality symmetry. Although the global continuous duality symmetries of dimensionally reduced heterotic supergravity are completely broken by the structure constants of the maximally enhanced gauge groups, the low energy effective action can be written in a manifestly duality covariant form using heterotic double field theory. As a byproduct, we show that a unique deformation of the generalized diffeomorphisms accounts for both SO(32) and E8×E8 heterotic effective field theories, which can thus be considered two different backgrounds of the same double field theory even before compactification. Finally we discuss the spontaneous gauge symmetry breaking and Higgs mechanism that occurs when slightly perturbing the background fields, both from the string and the field theory perspectives.
​
https://arxiv.org/abs/1805.11128
​
JOURNAL CLUB
12/04/18, 14H (Aula Chica)
Speaker: Yago Cagnacci
Brane Wess-Zumino terms from AKSZ and exceptional generalised geometry as an L∞-algebroid
​
We reinterpret the generalised Lie derivative of M-theory E6 generalised geometry as hamiltonian flow on a graded symplectic supermanifold. The hamiltonian acts as the nilpotent derivative of the tensor hierarchy of exceptional field theory. This construction is an M-theory analogue of the Courant algebroid and reveals the L∞-algebra underlying the tensor hierarchy. The AKSZ construction identifies that same hamiltonian with the lagrangian of a 7-dimensional generalisation of Chern-Simons theory that reduces to the M5-brane Wess-Zumino term on 5-brane boundaries. The exercise repeats for the type IIB E5 generalised geometry and we discuss the relation to the D3-brane.
​
https://arxiv.org/abs/1804.07303
​
JOURNAL CLUB
31/05/18, 13H (Aula Chica)
Speaker: Eric Lescano
AKSZ Sigma-models
​
JOURNAL CLUB
07/05/18, 13H (Aula Chica)
​
Speaker: Carmen Nuñez
Symmetry enhancement interpolation, non-commutativity and Double Field Theory
G. Aldazabal, E. Andrés, M.Mayo, V. Penas
​
We present a moduli dependent target space effective field theory action for (truncated) heterotic string toroidal compactifications. When moving continuously along moduli space, the stringy gauge symmetry enhancement-breaking effects, which occur at particular points of moduli space, are reproduced. Besides the expected fields, originated in the ten dimensional low energy effective theory, a new vector and scalar fields are included. These fields depend on "double periodic coordinates" as usually introduced in Double Field Theory. Their mode expansion encodes information about string states, carrying winding and KK momenta, associated to gauge symmetry enhancements. Interestingly enough, it is found that a non-commutative product, which introduces an intrinsic non-commutativity on the compact target space, is required in order to make contact with string theory amplitude results.
​
JOURNAL CLUB
14/05/18, 13H (Aula Chica)
​
Speaker: Diego Marques
O(D,D)-constraint on D-dimensional effective actions
​
Double Field Theory is a manifestly T-duality invariant formulation of string theory in which the effective theory at any order of α′ is invariant under global O(D,D) transformations and ought to be invariant under gauge transformations which receive α′-corrections. On the other hand, the effective theory in the usual D-dimensional formulation of string theory is manifestly gauge invariant and ought to be invariant under T-duality transformations which receive α′-corrections. We speculate that the combination of these two constraints may fix both the 2D-dimensional and the D-dimensional effective actions without knowledge of the α′-corrections of the gauge and the T-duality transformations.
In this paper, using generalized fluxes, we construct arbitrary O(D,D)-invariant actions at orders α′0 and α′, and then dimensionally reduce them to the D-dimensional spacetime. On the other hand, at these orders, we construct arbitrary covariant D-dimensional actions. Constraining the two D-dimensional actions to be equal up to non-covariant field redefinitions, we find that both actions are fixed up to overall factors and up to field redefinitions.
​
Workshop on Geometry and Duality in String Theory
29-30/10/18, 13H
​
International Center for Advanced Studies
​
JOURNAL CLUB
01/11/18, 13H (Aula Chica)
​
Speaker: Ale Rodriguez
​
T-dual cosmological solutions in double field theory
We investigate the cosmological solutions coming from the double field theory equations of motion after coupling a matter source to them. Assuming constant dilaton and imposing the section condition with respect to the regular coordinates leads to a universe dominated by momentum modes while imposing the section condition with respect to the dual coordinates naturally leads to a universe dominated by momentum modes. We show that both regimes have asymptotic behaviours related by T-duality. This hints towards defining a duality between the clocks considered in each regime and interpreting winding modes as being radiation from the point of view of a Euclidean time.
​
JOURNAL CLUB
08/11/18, 12:30H (Aula Chica)
​
Speaker: Carmen Nuñez
​
O(D,D) gauge fields in the T-dual string Lagrangian
Machiko Hatsuda, Warren Siegel
​
We present the string Lagrangian with manifest T-duality. Not only zero-modes but also all string modes are doubled. The gravitational field is an O(D,D) gauge field. We give a Lagrangian version of the section condition for the gauge invariance which compensates the O(D,D) transformation from the gravitational field and the GL(2D) coordinate transformation. We also show the gauge invariance of the line element of the manifest T-duality space and the O(D,D) condition on the background. Different sections describe dual spaces.
​
JOURNAL CLUB
05/11/18, 12:30H (Aula Chica)
​
Speaker: Ale Rodriguez
​
Dual Space-Time and Nonsingular String Cosmology
Robert Brandenberger, Renato Costa, Guilherme Franzmann, Amanda Weltman
Making use of the T-duality symmetry of superstring theory, and of the double geometry from Double Field Theory, we argue that cosmological singularities of a homogeneous and isotropic universe disappear. In fact, an apparent big bang singularity in Einstein gravity corresponds to a universe expanding to infinite size in the dual dimensions.
​