strings@iafe
String Theory Group at Instituto de Astronomía y Física del Espacio, Buenos Aires, Argentina
SEMINARS 2019
JOURNAL CLUB
28/02/19, 14H (Aula Chica)
Speaker: Tomas Codina
L∞ algebras and Tensor Hierarchies in Exceptional Field Theory and Gauged Supergravity
Yago Cagnacci, Tomas Codina, Diego Marques
We show how the gauge and field structure of the tensor hierarchies in Double and E7(7) Exceptional Field Theory fits into L∞ algebras. Special attention is paid to redefinitions, the role of covariantly constrained fields and intertwiners. The results are connected to Gauged Supergravities through generalized Scherk-Schwarz reductions. We find that certain gauging-dependent parameters generate trivial gauge transformations, giving rise to novel symmetries for symmetries that are absent in their ungauged counterparts.
https://arxiv.org/abs/1807.06028
JOURNAL CLUB
15/03/19, 13:00H (Aula Chica)
Speaker: Diego Marques
Higher Gauge Structures in Double and Exceptional Field Theory
JOURNAL CLUB
22/03/19, 13:00H (Aula Chica)
Speaker: Tomas Codina
R4 terms in supergravities via T-duality constraint
Hamid Razaghian, Mohammad R. Garousi
JOURNAL CLUB
05/04/19, 14:00H (Aula Chica)
Speaker: Ale Rodriguez
New Cosmological Signatures from Double Field Theory
JOURNAL CLUB
10/04/19, 14:00H (Aula Chica)
Speaker: Gabriel Scoccola
String Gas Cosmology
String gas cosmology is a string theory-based approach to early universe cosmology which is based on making use of robust features of string theory such as the existence of new states and new symmetries. A first goal of string gas cosmology is to understand how string theory can effect the earliest moments of cosmology before the effective field theory approach which underlies standard and inflationary cosmology becomes valid. String gas cosmology may also provide an alternative to the current standard paradigm of cosmology, the inflationary universe scenario. Here, the current status of string gas cosmology is reviewed.
JOURNAL CLUB
26/04/19, 14:00H (Aula Chica)
Speaker: Carmen Nuñez
Aspects of Quartic Riemann Interactions
JOURNAL CLUB
03/05/19, 14:00H (Aula Chica)
Speaker: Eric Lescano
Double supergeometry
A geometry of superspace corresponding to double field theory is developed, with type II supergravity in D=10 as the main example. The formalism is based on an orthosymplectic extension OSp(d,d|2s) of the continuous T-duality group. Covariance under generalised super-diffeomorphisms is manifest. Ordinary superspace is obtained as a solution of the orthosymplectic section condition. A systematic study of curved superspace Bianchi identities is performed, and a relation to a double pure spinor superfield cohomology is established. A Ramond-Ramond superfield is constructed as an infinite-dimensional orthosymplectic spinor. Such objects in minimal orbits under the OSp supergroup ("pure spinors") define super-sections.
JOURNAL CLUB
10/05/19, 14:00H (Aula Chica)
Speaker: Tomas Codina
T-duality Constraints on Higher Derivatives Revisited
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.
JOURNAL CLUB
17/05/19, 14:00H (Aula Chica)
Speaker: Diego Marques
Non-Abelian T-duality as a Transformation in Double Field Theory
Non-Abelian T-duality (NATD) is a solution generating transformation for supergravity backgrounds with non-Abelian isometries. We show that NATD can be described as a coordinate dependent O(d,d) transformation, where the dependence on the coordinates is determined by the structure constants of the Lie algebra associated with the isometry group. Besides making calculations significantly easier, this approach gives a natural embedding of NATD in Double Field Theory (DFT), which provides an O(d,d) covariant formulation for effective string actions. As a result of this embedding, it becomes easy to prove that the NATD transformed backgrounds solve supergravity equations, when the isometry algebra is unimodular. If the isometry algebra is non-unimodular, the generalised dilaton field is forced to have a linear dependence on the dual coordinates, and hence the resulting background solves generalised supergravity equations.
JOURNAL CLUB
24/05/19, 14:00H (Aula Chica)
Speaker: Carmen Nuñez
Four-derivative couplings via T-duality constraint
We examine the proposal that the dimensional reduction of the effective action of perturbative string theory on a circle, should be invariant under T-duality transformations. The T-duality transformations are the standard Buscher rules plus some higher covariant derivatives. By explicit calculations at order α′ for metric, dilaton and B-field, we show that the T-duality constraint can fix both the effective action and the higher derivative corrections to the Buscher rules up to an overall factor. The corrections depend on the scheme that one uses for the effective action. We have found the effective action and its corresponding T-duality transformations in an arbitrary scheme.
JOURNAL CLUB
28/05/19, 13:00H (Aula Chica)
Speaker: Ale Rodriguez
O(D,D) completion of the Friedmann equations
Stephen Angus, Kyoungho Cho, Guilherme Franzmann, Shinji Mukohyama, Jeong-Hyuck Park
String theory suggests a unique and unambiguous modification to General Relativity: the symmetry of O(D,D) T-duality promotes the entire closed-string massless NS-NS sector to stringy graviton fields. The symmetry fixes the couplings to other matter fields unambiguously and the Einstein field equations are enriched to comprise D2+1 components, dubbed recently as the Einstein Double Field Equations. Here we explore the cosmological implications of this `Stringy Gravity'. We derive the most general homogeneous and isotropic ansatzes for both stringy graviton fields and the stringy energy-momentum tensor. Substituting them into the Einstein Double Field Equations, we obtain the O(D,D) completion of the Friedmann equations along with a generalized continuity equation. We discuss how this gives an enriched and novel framework beyond typical string cosmology, with solutions that may be characterized by two equation-of-state parameters, w (conventional) and λ (new). When λ+3w=1, the dilaton remains constant throughout the cosmological evolution, and one recovers the standard Friedmann equations for generic matter content (i.e. for any w), an improvement over conventional string cosmology where this occurs only for a radiation equation of state (w=1/3). We further point out that, in contrast to General Relativity, in Stringy Gravity there is no de Sitter solution arising from either an O(D,D)-symmetric cosmological constant or scalar field with positive energy density.
JOURNAL CLUB
04/06/19, 13:00H (Aula Chica)
Speaker: Tomas Codina
Duality Invariant Cosmology to all Orders in α′
While the classification of α′ corrections of string inspired effective theories remains an unsolved problem, we show how to classify duality invariant α′ corrections for purely time-dependent (cosmological) backgrounds. We determine the most general duality invariant theory to all orders in α′ for the metric, b-field, and dilaton. The resulting Friedmann equations are studied when the spatial metric is a time-dependent scale factor times the Euclidean metric and the b-field vanishes. These equations can be integrated perturbatively to any order in α′. We construct non-perturbative solutions and display duality invariant theories featuring string-frame de Sitter vacua.
JOURNAL CLUB
11/06/19, 13:00H (Aula Chica)
Speaker: Walter Baron
Uplifts of maximal supergravities and transitions to non-geometric vacua
Gianguido Dall'Agata, Gianluca Inverso, Paolo Spezzati
We describe a new procedure to obtain consistent backgrounds that uplift vacua and deformations of various maximal gauged supergravities by taking a known solution and performing singular limits along the moduli space of the corresponding 4-dimensional theory. We then apply this procedure to the S^3 x H^{2,2} background that provides the uplift of 4-dimensional Minkowski vacua of maximal supergravity with gauge group [SO(4) x SO(2,2)] ⋉ R^{16}. We find that the newly generated vacua are generally only locally geometric and correspond to asymmetric orbifolds, Q-flux backgrounds or combinations thereof. We also provide the uplift to eleven dimensions of all the four-parameter Cremmer-Scherk-Schwarz gaugings.
JOURNAL CLUB
18/06/19, 13:00H (Aula Chica)
Speaker: Lucas Finazzi
Superspace formulations of ten-dimensional supergravity
We present a new formulation for N=1, D=10 supergravity in superspace, in presence of a Lorentz Chern-Simons-form. This formulation entails the following properties: it furnishes a solution of the Bianchi identities that is algebraically consistent to all orders in alpha'; at first order it is the simplest formulation proposed so far, and it is therefore most suitable for an explicit higher order analysis; it allows a well defined perturbative expansion in alpha', in which no poltergeist fields appear; it reconciles the two different classes of first order solutions available in the literature, that until now appeared physically inequivalent.
JOURNAL CLUB
02/07/19, 13:00H (Aula Chica)
Speaker: Diego Marques
Kerr-Schild Double Field Theory and Classical Double Copy
The Kerr-Schild (KS) formalism is a powerful tool for constructing exact solutions in general relativity. In this paper, we present a generalization of the conventional KS formalism to double field theory (DFT) and supergravities. We introduce a generalized KS ansatz for the generalized metric in terms of a pair of null vectors. Applying this ansatz to the equations of motion of DFT, we construct the generalized KS field equation. While the generalized KS equations are quadratic in the fields, we show that it is possible to find solutions by considering linear equations only. Furthermore, we construct a Killing spinor equation under the generalized KS ansatz. Based on this formalism, we show that the classical double copy structure, which represents solutions of the Einstein equation in terms of solutions of the Maxwell equation, can be extended to the entire massless string NS-NS sector. We propose a supersymmetric classical double copy which shows that solutions of the Killing spinor equation can be realized in terms of solutions of the BPS equation of the supersymmetric Maxwell theory.