strings@iafe
String Theory Group at Instituto de AstronomÃa y FÃsica del Espacio, Buenos Aires, Argentina
SEMINARS 2016​
JOURNAL CLUB
16/03/16, 14H
Speaker: Eric Lescano
HSZ theory to first order in alpha-prime
Práctica de defensa de tesis de Licenciatura.
JOURNAL CLUB
30/03/16, 14H
Aula Chica.
Speaker: Diego Marques
Three-point Functions in Duality-Invariant Higher-Derivative Gravity
Usman Naseer, Barton Zwiebach
Doubled \alpha'-geometry is the simplest higher-derivative gravitational theory with exact global duality symmetry. We use the double metric formulation of this theory to compute on-shell three-point functions to all orders in \alpha'. A simple pattern emerges when comparing with the analogous bosonic and heterotic three-point functions. As in these theories, the amplitudes factorize. The theory has no Gauss-Bonnet term, but contains a Riemann-cubed interaction to second order in \alpha'.
SEMINAR
7/04/16, 14H
Speaker: Walter Baron
Gaugings from E7 Exceptional Field Theory
We discuss the state of the art in the construction of both compact and
non compact gaugings in Gauged Supergravities from fluxes in U-dual
extensions of Double Field Theories.
JOURNAL CLUB
18/04/16, 14H
Aula Chica.
Speaker: Yago Cagnacci
Enhanced gauge symmetry and winding modes in Double Field Theory with non trivial B-field
For some special values of the moduli In a n-toroidal compactification of the bosonic string, there are additional massless particles that enhance the (U(1) × U(1))^n gauge symmetry to simply-laced laced groups. I will discuss an explicit example (in n=2 with non trivial B field) of how these particles can be incorporated in double field theory.
JOURNAL CLUB
25/04/16, 14H
Aula Chica.
Speaker: Carmen Nuñez.
Dual Double Field Theory
Eric A. Bergshoeff, Olaf Hohm, Victor A. Penas, Fabio Riccioni
We present the dual formulation of double field theory at the linearized level. This is a classically equivalent theory describing the duals of the dilaton, the Kalb-Ramond field and the graviton in a T-duality or O(D,D) covariant way. In agreement with previous proposals, the resulting theory encodes fields in mixed Young-tableau representations, combining them into an antisymmetric 4-tensor under O(D,D). In contrast to previous proposals, the theory also requires an antisymmetric 2-tensor and a singlet, which are not all pure gauge. The need for these additional fields is analogous to a similar phenomenon for "exotic" dualizations, and we clarify this by comparing with the dualizations of the component fields. We close with some speculative remarks on the significance of these observations for the full non-linear theory yet to be constructed.
JOURNAL CLUB
29/06/16, 14H
Aula Chica.
Speaker: Mario Galante.
The Unity of Cosmological Attractors
Mario Galante, Renata Kallosh, Andrei Linde, Diederik Roest
Recently, several broad classes of inflationary models have been discovered whose cosmological predictions are stable with respect to significant modifications of the inflaton potential. Some classes of models are based on a non-minimal coupling to gravity. These models, which we will call ξ-attractors, describe universal cosmological attractors (including Higgs inflation) and induced inflation models. Another class describes conformal attractors (including Starobinsky inflation and T-models) and their generalization to α-attractors. The aim of this paper is to elucidate the common denominator of these models: their attractor properties stem from a pole of order two in the kinetic term of the inflaton field in the Einstein frame formulation, prior to switching to the canonical variables. We point out that α- and universal attractors differ in the subleading corrections to the kinetic term. As a final step towards unification of ξ and α attractors, we introduce a special class of ξ-attractors which is fully equivalent to α-attractors with the identification α=1+16ξ. There is no theoretical lower bound on r in this class of models.
SEMINAR
06/07/16, 14H
Aula Chica.
Speaker: Victor Penas.
Properties of Double Field Theory
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Based on:
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https://arxiv.org/abs/1508.00780
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&
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JOURNAL CLUB
04/08/16, 14H
Aula Chica.
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Speaker: Eric Lescano.
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On the curious spectrum of duality invariant higher-derivative gravity
Olaf Hohm, Usman Naseer, Barton Zwiebach
We analyze the spectrum of the exactly duality and gauge invariant higher-derivative double field theory. While this theory is based on a chiral CFT and does not correspond to a standard string theory, our analysis illuminates a number of issues central in string theory. The full quadratic action is rewritten as a two-derivative theory with additional fields. This allows for a simple analysis of the spectrum, which contains two massive spin-2 ghosts and massive scalars, in addition to the massless fields. Moreover, in this formulation, the massless or tensionless limit α′→∞ is non-singular and leads to an enhanced gauge symmetry. We show that the massive modes can be integrated out exactly at the quadratic level, leading to an infinite series of higher-derivative corrections. Finally, we present a ghost-free massive extension of linearized double field theory, which employs a novel mass term for the dilaton and metric.
JOURNAL CLUB
18/08/16, 14H
Aula Chica.
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Speaker: Emanuel Malek.
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D-branes and M-branes in DFT/EFT/GG/EGG
JOURNAL CLUB
01/09/16, 14H
Aula Chica.
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Speaker: Carmen Nuñez.
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On Cosmological Constants from alpha'-Corrections
Friðrik Freyr Gautason, Daniel Junghans, Marco Zagermann
We examine to what extent perturbative alpha'-corrections can generate a small cosmological constant in warped string compactifications. Focusing on the heterotic string at lowest order in the string loop expansion, we show that, for a maximally symmetric spacetime, the alpha'-corrected 4D scalar potential has no effect on the cosmological constant. The only relevant terms are instead higher order products of 4D Riemann tensors, which, however, are found to vanish in the usual perturbative regime of the alpha'-expansion. The heterotic string therefore only allows for 4D Minkowski vacua to all orders in alpha', unless one also introduces string loop and/or nonperturbative corrections or allows for curvatures or field strengths that are large in string units. In particular, we find that perturbative alpha'-effects cannot induce weakly curved AdS_4 solutions.
JOURNAL CLUB
08/09/16, 14H
Aula Chica.
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Speaker: Diego Marques.
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Black hole thermodynamics, stringy dualities and double field theory
Alex S. Arvanitakis, Chris D. A. Blair
We discuss black hole thermodynamics in the manifestly duality invariant formalism of double field theory (DFT). We reformulate and prove the first law of black hole thermodynamics in DFT, using the covariant phase space approach. After splitting the full O(D, D) invariant DFT into a Kaluza-Klein-inspired form where only n coordinates are doubled, our results provide explicit duality invariant mass and entropy formulas. We illustrate how this works by discussing the black fundamental string solution and its T-duals.
JOURNAL CLUB
16/09/16, 14H
Aula Chica.
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Speaker: Sergio Iguri.
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Basics of Inflation
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A discussion on the first chapters of https://arxiv.org/abs/0907.5424 by Daniel Baumann.
JOURNAL CLUB
29/09/16, 14H
Aula Chica.
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Speaker: Victor Penas.
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Doubled strings, negative strings and null waves
We revisit the fundamental string (F1) solution in the doubled formalism. We show that the wave-like solution of double field theory (DFT) corresponding to the F1/pp-wave duality pair is more properly a solution of the DFT action coupled to a doubled sigma model action. The doubled string configuration which sources the pp-wave can be thought of as static gauge with the string oriented in a dual direction. We also discuss the DFT solution corresponding to a vibrating string, carrying both winding and momentum. We further show that the solution dual to the F1 in both time and space can be viewed as a "negative string" solution. Negative branes are closely connected to certain exotic string theories which involve unusual signatures for both spacetime and brane worldvolumes. In order to better understand this from the doubled point of view, we construct a variant of DFT suitable for describing theories in which the fundamental string has a Euclidean worldsheet, for which T-dualities appear to change the spacetime signature.
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LECTURES
31/08/16 - 11/09/16, Departamento de física UBA.
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Speaker: Mariana Graña.
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VI Lectures on flux compactifications in String Theory
Lecture 1: Consistent truncations.
Lecture 2: Kaluza-Klein compactifications.
Lecture 3: Scherk-Schwarz compactifications.
Lecture 4: Calabi-Yau compactifications.
Lecture 5: N=2 supergravities in D=4.
Lecture 6: Generalized Geometry.
JOURNAL CLUB
Second semester 2016, IAFE.
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IV topics in inflation and string theory
JC1: Gabriel Leon "Slow-roll inflation".
JC2: Susana Landau "The CMB power spectrum".
JC3: Diego Marques "Effective potentials form flux compactifications of string theory".
JC4: Mario Galante "Warped branes and inflation".
JOURNAL CLUB
02/12/16, 14H
Aula Chica.
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Speaker: Eric Lescano.
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Second order higher-derivative corrections in Double Field Theory
HSZ Double Field Theory is a higher-derivative theory of gravity with exact and manifest T-duality symmetry. The first order corrections in the massless sector were shown to be governed solely by Chern-Simons deformations of the three-form field strength. We compute the full action with up to six derivatives O(α′2) for the universal sector containing the metric, two-form and dilaton fields. The Green-Schwarz transformation of the two-form field remains uncorrected to second order. In addition to the expected Chern-Simons-squared and Riemann-cubed terms the theory contains a cubic Gauss-Bonnet interaction, plus other six-derivative unambiguous terms involving the three-form field strength whose presence indicates that the theory must contain further higher-derivative corrections.
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JOURNAL CLUB
09/12/16, 14H
Aula Chica.
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Speaker: Yago Cagnacci.
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Gauge enhancement in DFT: stringy-sized tori.
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