strings@iafe
String Theory Group at Instituto de AstronomÃa y FÃsica del Espacio, Buenos Aires, Argentina
SEMINARS 2017​
JOURNAL CLUB
05/04/17, 14H (Aula Chica)
Speaker: Eric Lescano
Background Independent Double Field Theory at Order α′: Metric vs. Frame-like Geometry
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The higher derivative corrections in double field theory are revisited to first order in α′. In first order perturbation theory around flat space, the gauge algebra is α′corrected, governed by two parameters a,b. One parameter choice corresponds to bosonic string theory, another to heterotic string theory. These results are generalized to second order in perturbation theory by a Noether procedure. Using consistency conditions derived from the Jacobi identity, it is shown that for general a,b there is no generalized metric formulation. A manifestly background independent formulation is instead given by a frame formalism, with α′-deformed frame transformations, as proposed by Marques and Nunez. Their construction is slightly generalized to an α′-deformed GL(D)×GL(D) frame formalism. The perturbation theory around flat space is matched to second order with the results obtained by the Noether procedure. We also obtain a formulation based on the `non-symmetric' metric E, the sum of metric and b-field. The transformations of E under O(D,D) receive non-trivial α′ corrections, unless a=−b, in which case there is a generalized metric formulation, in agreement with previous results in the literature.
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JOURNAL CLUB
20/04/17, 14H (Aula Chica)
Speaker: Diego Marques
Relating duality covariant formulations of alpha-prime corrections.
JOURNAL CLUB
27/04/17, 14H (Aula Chica)
Speaker: Yago Cagnacci
The bosonic string on string-size tori from double field theory
Yago Cagnacci, Mariana Graña, Sergio Iguri, Carmen Núñez
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We construct the effective action for toroidal compactifications of bosonic string theory from generalized Scherk-Schwarz reductions of double field theory. The enhanced gauge symmetry arising at special points in moduli space is incorporated into this framework by promoting the O(k,k) duality group of k-tori compactifications to O(n,n), n being the dimension of the enhanced gauge group, which allows to account for the full massless sector of the theory. We show that the effective action reproduces the right masses of scalar and vector fields when moving sligthly away from the points of maximal symmetry enhancement. The neighborhood of the enhancement points in moduli space can be neatly explored by spontaneous symmetry breaking. We generically discuss toroidal compactifications of arbitrary dimensions and maximally enhanced gauge groups, and then inspect more closely the example of T2 at the SU(3)L×SU(3)Rpoint, which is the simplest setup containing all the non trivialities of the generic case. We show that the entire moduli space can be described in a unified way by considering compactifications on higher dimensional tori.
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Strings@ar Lectures on Advanced Topics of High Energy Physics
15/05/17 (Aula Seminarios, IAFE)
Juan Martin Maldacena, IAS, Princeton
Program:
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1st Lecture, 10:00 - 11.15 hs : Motivations. The Sachdev-Ye-Kitaeev model and some of its propertie. Variations of the models.
2nd Lecture: 11:45 - 13:00 hs : Details of the model. Low energy limit. Low energy degrees of freedom related to reparametrizaitnos.​
3rd Lecture: 14:30 - 15:45 hs : Black holes close to extremality and AdS2. Gravity dynamics in AdS2 spaces. Similarities with Sachdev-Ye-Kitaeev.
JOURNAL CLUB
11/05/17, 14H (Aula Chica)
Speaker: Carmen Nuñez
Noncompact Symmetries in String Theory (Back to the future)
Jnan Maharana, John H. Schwarz
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Noncompact groups, similar to those that appeared in various supergravity theories in the 1970's, have been turning up in recent studies of string theory. First it was discovered that moduli spaces of toroidal compactification are given by noncompact groups modded out by their maximal compact subgroups and discrete duality groups. Then it was found that many other moduli spaces have analogous descriptions. More recently, noncompact group symmetries have turned up in effective actions used to study string cosmology and other classical configurations. This paper explores these noncompact groups in the case of toroidal compactification both from the viewpoint of low-energy effective field theory, using the method of dimensional reduction, and from the viewpoint of the string theory world sheet. The conclusion is that all these symmetries are intimately related. In particular, we find that Chern--Simons terms in the three-form field strength Hμνρplay a crucial role.
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Lectures on supergravity
June - July, IAFE (Aula Chica)
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Speaker: Diego Marqués
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Topics:
1) N=1 in D=4.
2) N=1 in D=10.
3) N=1 in D=10 in DFT.
4) D=11 sugra.
5) N=2 in D=10.
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Each item discuses: susy transformations, closure, action, invariance, Leichnerowicz formula, etc.
JOURNAL CLUB
29/06/17, 14H (Aula Chica)
Speaker: Diego Marques
Duality Twisted Reductions of Double Field Theory of Type II Strings
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We study duality twisted reductions of the Double Field Theory (DFT) of the RR sector of massless Type II theory, with twists belonging to the duality group Spin+(10,10). We determine the action and the gauge algebra of the resulting theory and determine the conditions for consistency. In doing this, we work with the DFT action constructed by Hohm, Kwak and Zwiebach, which we rewrite in terms of the Mukai pairing: a natural bilinear form on the space of spinors, which is manifestly Spin(n,n) invariant. The fact that Lie algebras of Spin(n,n) and SO(n,n) are isomorphic plays a crucial role in all the calculations. The DFT of the RR sector couples to that of the NS-NS sector, so the latter should also be reduced with a compatible duality twist. If the duality twist is introduced via the Spin+(10,10) element S in the RR sector, then the NS-NS sector should be deformed via the duality twist U = ρ(S), where ρ is the double covering homomorphism between Pin(n,n) and O(n,n). We show that the set of conditions required for the consistency of the reductions of the two sectors are equivalent. However, requirement of compatibility of the reductions imposes an extra condition on the dilaton anzats, which is not evident from the analysis of the NS-NS sector alone.
JOURNAL CLUB
06/07/17, 14H (Aula Chica)
Speaker: Yago Cagnacci
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The moduli space of heteortic compactifications
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JOURNAL CLUB
13/07/17, 14H (Aula Chica)
Speaker: Eric Lescano
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Exceptional Field Theory I: E6(6) covariant Form of M-Theory and Type IIB
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We present the details of the recently constructed E6(6) covariant extension of 11-dimensional supergravity. This theory requires a 5+27 dimensional spacetime in which the `internal' coordinates transform in the 27¯ of E6(6). All fields are E6(6) tensors and transform under (gauged) internal generalized diffeomorphisms. The `Kaluza-Klein' vector field acts as a gauge field for the E6(6) covariant `E-bracket' rather than a Lie bracket, requiring the presence of two-forms akin to the tensor hierarchy of gauged supergravity. We construct the complete and unique action that is gauge invariant under generalized diffeomorphisms in the internal and external coordinates. The theory is subject to covariant section constraints on the derivatives, implying that only a subset of the extra 27 coordinates is physical. We give two solutions of the section constraints: the first preserves GL(6) and embeds the action of the complete (i.e. untruncated) 11-dimensional supergravity; the second preserves GL(5) x SL(2) and embeds complete type IIB supergravity. As a by-product, we thus obtain an off-shell action for type IIB supergravity.
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JOURNAL CLUB
17/08/17, 12:30H (Aula Chica)
Speaker: Diego Marques
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The exceptional story of massive IIA supergravity
Franz Ciceri, Adolfo Guarino, Gianluca Inverso
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The framework of exceptional field theory is extended by introducing consistent deformations of its generalised Lie derivative. For the first time, massive type IIA supergravity is reproduced geometrically as a solution of the section constraint. This provides a unified description of all ten- and eleven-dimensional maximal supergravities. The action of the E7 deformed theory is constructed, and reduces to those of exceptional field theory and gauged maximal supergravity in respective limits. The relation of this new framework to other approaches for generating the Romans mass non-geometrically is discussed.
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JOURNAL CLUB
23/08/17, 13H (Aula Chica)
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Speaker: Yago Cagnacci
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L∞ Algebras and Field Theory
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We review and develop the general properties of L∞ algebras focusing on the gauge structure of the associated field theories. Motivated by the L∞ homotopy Lie algebra of closed string field theory and the work of Roytenberg and Weinstein describing the Courant bracket in this language we investigate the L∞structure of general gauge invariant perturbative field theories. We sketch such formulations for non-abelian gauge theories, Einstein gravity, and for double field theory. We find that there is an L∞ algebra for the gauge structure and a larger one for the full interacting field theory. Theories where the gauge structure is a strict Lie algebra often require the full L∞ algebra for the interacting theory. The analysis suggests that L∞ algebras provide a classification of perturbative gauge invariant classical field theories.
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SEMINAR
30/08/17, 13H (Aula Chica)
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Speaker: Raju Roychowdhury
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Emergent Gravity and Geometric T-duality
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Darboux theorem and Moser lemma in symplectic geometry are the two essential ingredients of emergent gravity. Generalized geometry naturally provides the framework for such a systematic approach to non-symmetric metric gravity and gives rise to the group of Courant automorphism $Diff(M) \ltimes \Omega_{closed}^{2}(M)$ for the Pontryagin bundle $TM \oplus T^*M$. As further consequences of generalized geometry and Courant algebroid structure we found the imprints of Dirac structure in emergent gravity. The non-degeneracy and closure of the symplectic 2-form enable us to set up a connection between emergent gravity and Big isotropic structure of Vaisman. Finally we propose a geometric T-dual of emergent gravity implemented between oriented circle bundles and this duality is realized in terms of Gysin sequence in the cohomology.
JOURNAL CLUB
06/09/17, 13H (Aula Chica)
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Speaker: Eric Lescano
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Classification of non-Riemannian doubled-yet-gauged spacetime
Kevin Morand, Jeong-Hyuck Park
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Assuming O(D,D) covariant fields as the `fundamental' variables, Double Field Theory can accommodate novel geometries where Riemannian metric cannot be defined, even locally. Here we present a complete classification of such non-Riemannian spacetimes in terms of two non-negative integers, (n,n¯), 0≤n+n¯≤D. Upon these backgrounds, strings become chiral and anti-chiral over n and n¯ directions respectively, while particles and closed strings are frozen over the n+n¯ directions. In particular, we identify (0,0) as Riemannian manifolds, (1,0) as non-relativistic spacetime, (1,1) as Gomis-Ooguri non-relativistic string, (D−1,0) as ultra-relativistic Carroll geometry, and (D,0) as Siegel's chiral string. Combined with a covariant Kaluza-Klein ansatz which we further spell, (0,1) leads to Newton-Cartan gravity. Alternative to the conventional string compactifications on small manifolds, non-Riemannian spacetime such as D=10, (3,3) may open a new scheme of the dimensional reduction from ten to four.
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JOURNAL CLUB
13/09/17, 13H (Aula Chica)
Speaker: Walter Baron
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Generalised Scherk-Schwarz reductions from gauged supergravity
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A procedure is described to construct generalised Scherk-Schwarz uplifts of gauged supergravities. The internal manifold, fluxes, and consistent truncation Ansatz are all derived from the embedding tensor of the lower-dimensional theory. The construction exhausts the class of generalised parallelisable spaces where the vector components of the frame are embedded in the adjoint representation of the gauge group as specified by the embedding tensor. This allows to recover the generalised Scherk-Schwarz reductions known in the literature and to prove a no-go result for the uplift of ω-deformed SO(p,q) gauged maximal supergravities.
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JOURNAL CLUB
20/09/17, 13H (Aula Chica)
Speaker: Sergio Iguri
Poisson-Lie T-Duality in Double Field Theory
We present a formulation of Double Field Theory with a Drinfeld double as extended spacetime. It makes Poisson-Lie T-duality (including abelian and non-abelian T-duality as special cases) manifest. This extends the scope of possible applications of the theory, which so far captured abelian T-duality only, considerably. The full massless bosonic subsector (NS/NS and R/R) of type II string theories is covered.
JOURNAL CLUB
27/09/17, 13H (Aula Chica)
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Speaker: Carmen Nuñez
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O(d+1,d+1) enhanced double field theory
Olaf Hohm, Edvard T. Musaev, Henning Samtleben
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Double field theory yields a formulation of the low-energy effective action of bosonic string theory and half-maximal supergravities that is covariant under the T-duality group O(d,d) emerging on a torus Td. Upon reduction to three spacetime dimensions and dualisation of vector fields into scalars, the symmetry group is enhanced to O(d+1,d+1). We construct an enhanced double field theory with internal coordinates in the adjoint representation of O(d+1,d+1). Its section constraints admit two inequivalent solutions, encoding in particular the embedding of D=6 chiral and non-chiral theories, respectively. As an application we define consistent generalized Scherk-Schwarz reductions using a novel notion of generalized parallelization. This allows us to prove the consistency of the truncations of D=6, N=(1,1) and D=6, N=(2,0) supergravity on AdS3×S3.
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JOURNAL CLUB
12/10/17, 13H (Aula Chica)
Speaker: Ale Rodriguez
N=1 Supersymmetric Double Field Theory
We construct the N=1 supersymmetric extension of double field theory for D=10, including the coupling to an arbitrary number n of abelian vector multiplets. This theory features a local O(1,9+n) x O(1,9) tangent space symmetry under which the fermions transform. It is shown that the supersymmetry transformations close into the generalized diffeomorphisms of double field theory.
JOURNAL CLUB
04/10/17, 13H (Aula Chica)
Speaker: Yago Cagnacci
General constructions of L∞ algebras
Olaf Hohm, Vladislav Kupriyanov, Dieter Lust, Matthias Traube
We construct L∞ algebras for general `initial data' given by a vector space equipped with an antisymmetric bracket not necessarily satisfying the Jacobi identity. We prove that any such bracket can be extended to a 2-term L∞ algebra on a graded vector space of twice the dimension, with the 3-bracket being related to the Jacobiator. We then prove the significantly more general theorem that if the Jacobiator takes values in the image of any linear map that defines an ideal there is a 3-term L∞ algebra with a generally non-trivial 4-bracket. We discuss special cases such as the commutator algebra of octonions, its contraction to the `R-flux algebra', and the Courant algebroid.
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Programa de profesores visitantes UBA
Nov 2017 (Departamento de Física, UBA)