arXiv subjects

Walter H. Baron

Publications and source records attributed to Walter H. Baron.

18 recordsLinked to original sources

arXiv2026

Generalized Bergshoeff-de Roo identification in the Supergravity frame

The effective action of string theory has a highly constrained structure due to the numerous symmetries of the underlying theory. Recently, a method known as the Generalized Bergshoeff-de Roo identification was developed, which exploits diffeomorphism, Lorentz and gauge invariance, along with T-duality, to derive higher-derivative couplings in the effective action within the framework of Double Field Theory. This method has been revisited and further refined to generate couplings directly within the standard Supergravity framework.

hep-th↗

arXiv2025

The generalized Bergshoeff-de Roo identification

There are two main approaches to duality covariant first order higher derivative corrections to the heterotic string, one extending the duality structure and the other deforming the gauge transformations. In this paper we introduce a framework from which both approaches can be derived, proving their equivalence and extending them to higher orders.

hep-th↗

arXiv2025

The generalized Bergshoeff-de Roo identification II

We recently introduced a T-duality covariant mechanism to compute all-order higher-derivative interactions in the heterotic string. Here we extend the formalism to account for a two-parameter family of corrections that also include the bosonic string and HSZ theory. We use our result to compute the full second order Double Field Theory (DFT) for generic values of the parameters, including the generalized Green-Schwarz transformation and its invariant action.

hep-th↗

arXiv2025

$β$ symmetry in type II Supergravities

A non geometric sector of the duality group emerging in Kaluza-Klein reductions is realized as an effective symmetry in the low energy action of uncompactified type II theories. This is achieved by extending the so called $β$ symmetry of the universal NS-NS sector to the R-R sector of type IIA, IIB and massive type IIA.

hep-th↗

arXiv2025

Tri-vector symmetry of 11 dimensional supergravity

Kaluza-Klein reductions of 11-dimensional supergravity lead to exceptional global symmetries in lower dimensions. Certain non-geometric elements of these symmetries, parameterized by a tri-vector $γ$, are not inherited from the higher-dimensional local symmetries, but represent instead a symmetry enhancement produced by the isometries of the background. Here, we demonstrate how to realize this enhancement in 11 dimensions, as a symmetry principle with constrained parameters. We show that $γ$ transformations exchange the equations of motion of the metric and the three-form with their Bianchi identities, in a closed form, structuring them into tri-vector multiplets. Implementing this principle as an off-shell symmetry of the theory requires the introduction of a hierarchy of dual fields, including a six-form and a dual graviton in the initial levels.

hep-th↗

arXiv2025

$β$ symmetry of heterotic supergravity

The low energy effective action describing the Kaluza-Klein reduction of string theory on a $d$-torus possesses a continuous O($d, d$) global symmetry. The non-geometric piece of this symmetry, parameterized by a bi-vector $β$, was recently shown to effectively act as a hidden symmetry on the massless RR and universal NSNS fields of the ten dimensional parent theory, fixing their couplings. Here we extend the analysis of this symmetry to the massless gauge and fermion fields of heterotic supergravity. While the interactions of the boson fields are univocally fixed by $β$ symmetry, we find four bilinear and two quartic $β$ invariant combinations of fermions whose relative coefficients in the action must be determined by supersymmetry. Although not fully fixed, bilinear and quartic fermion couplings are strongly restricted by $β$ symmetry at leading order in $α'$.

hep-th↗

arXiv2023

Exploring the $β$ symmetry of supergravity

Kaluza-Klein reductions of low energy string effective actions possess a continuous $O(d,d) $ symmetry. The non-geometric elements of this group, parameterized by a bi-vector $β$, are not inherited from the symmetries of the higher-dimensional theory, but constitute instead a symmetry enhancement produced by the isometries of the background. The realization of this enhancement in the parent theory was recently defined as $β$ symmetry, a powerful tool that allows to avoid the field reparameterizations of the Kaluza-Klein procedure. In this paper we further explore this symmetry and its impact on the first order $α'$-corrections. We derive the $β$ transformation rules from the frame formulation of Double Field Theory (DFT), and connect them to the corresponding rules in the Metsaev-Tseytlin and Bergshoeff-de Roo supergravity schemes. It follows from our results that $β$ symmetry is a necessary condition for the uplift of string $α'$-expansions to DFT.

hep-th↗

arXiv2022

The $β$-symmetry of supergravity

Continuous O$(d,d)$ global symmetries emerge in Kaluza-Klein reductions of $D$-dimensional string supergravities to $D-d$ dimensions. We show that the non-geometric elements of this group effectively act in the $D$-dimensional parent theory as a hidden bosonic symmetry that fixes its couplings: the $β$-symmetry. We give the explicit $β$-transformations to first order in $α'$ and verify the invariance of the action as well as the closure of the transformation rules.

hep-th↗

arXiv2022

Duality covariant field redefinitions

We explore the role of the dilaton field on higher derivative supergravity within the framework of Double Field Theory and use it to fix the Lorentz non covariant field redefinitions connecting the metric and dilaton fields with the duality multiplets.

hep-th↗

arXiv2017

The Odd story of $α'$-corrections

The $α'$-deformed frame-like Double Field Theory (DFT) is a T-duality and gauge invariant extension of DFT in which generalized Green-Schwarz transformations provide a gauge principle that fixes the higher-derivative corrections. It includes all the first order $α'$-corrections of the bosonic and heterotic string low energy effective actions and of the Hohm-Siegel-Zwiebach $α'$-geometry. Here we gauge this theory and parameterize it in terms of a frame, a two-form, a dilaton, gauge vectors and scalar fields. This leads to a unified framework that extends the previous construction by including all duality constrained interactions in generic (gauged/super)gravity effective field theories in arbitrary number of dimensions, to first order in $α'$.

hep-th↗

arXiv2015

Uplifting Maximal Gauged Supergravities

Which theories have a higher dimensional origin in String/M-theory is a non trivial question and it is still far from being understood in the constrained scenario of maximal supergravities. After 35 years of progress in this direction we have found supporting evidence in favor of the idea that every electric maximal supergravity in 4 dimensions can be uplifted to M-theory. We will review the current understanding of this problem with special emphasis in the uplifting of non compact supergravities and their relation with Exceptional Generalised Geometry.

hep-th↗

arXiv2015

Uplifting non-compact gauged supergravities

We provide the M-theory uplift of de Sitter vacua of SO(5,3) and SO(4,4) gaugings of maximal supergravity in 4 dimensions. We find new non-compact backgrounds that are squashed hyperboloids with non-trivial flux for the 3-form potential. The uplift requires a new non-linear ansatz for the 11-dimensional metric and for the 3-form potential that reduces to the known one leading to the 7-sphere solution in the case of the SO(8) gauging.

hep-th↗

arXiv2014

Gaugings from E7 Extended Geometries

We discuss the construction of gaugings in recent models of E7 Extended Geometries, focusing on the two inequivalent SL(8) truncations of the theory. In these sectors the conditions for the generation of gaugings in the 36, 36', 420 and 420' representations of E7 can be compactly expressed in terms of objects which are in the fundamental representation of SL(8), making the search of solutions simpler. As an application we discuss the generation of SO(8) gaugings. In particular we show how the internal generalized vielbein for the seven sphere recently found by Nicolai et al. can be derived in a completely independent setting and we also prove that neither of these sectors is able to generate the new SO(8) dyonic gaugings, at least if the so called section conditions are implemented.

hep-th↗

arXiv2013

Quantum corrections to dynamical holographic thermalization: entanglement entropy and other non-local observables

We investigate the thermalization time scale in the planar limit of the SU(N) N=4 SYM plasma at strong yet finite 't Hooft coupling by considering its supergravity dual description, including the full O(alpha'^3) type IIB string theory corrections. We also discuss on the effects of the leading non-planar corrections. We use extended geometric probes in the bulk which are dual to different non-local observables in the N=4 SYM theory. This is carried out within the framework of dynamical holographic thermalization.

hep-th↗

arXiv2013

Dynamics of holographic thermalization

Dynamical evolution of thin shells composed by different kinds of degrees of freedom collapsing within asymptotically AdS spaces is explored with the aim of investigating models of holographic thermalization of strongly coupled systems. From the quantum field theory point of view this corresponds to considering different thermal quenches. We carry out a general study of the thermalization time scale using different parameters and space-time dimensions, by calculating renormalized space-like geodesic lengths and rectangular minimal area surfaces as extended probes of thermalization, which are dual to two-point functions and rectangular Wilson loops. Different kinds of degrees of freedom in the shell are described by their corresponding equations of state. We consider a scalar field, as well as relativistic matter, a pressureless massive fluid and conformal matter, which can be compared with the collapse of an AdS-Vaidya thin shell. Remarkably, for conformal matter, the thermalization time scale becomes much larger than the others. Furthermore, in each case we also investigate models where the cosmological constants of the inner and outer regions separated by the shell are different. We found that in this case only a scalar field shell collapses, and that the thermalization time scale is also much larger than the AdS-Vaidya case.

hep-th↗

arXiv2012

Strings and D-branes in curved space-time

In this thesis we study the AdS3 Wess-Zumino-Novikov-Witten model. We compute the Operator Product Expansion of primary fields as well as their images under the spectral flow automorphism in all sectors of the model by considering it as a Wick rotation of the H3+ coset model. We argue that the symmetries of the affine algebra require a truncation which establishes the closure of the fusion rules on the Hilbert space of the theory. These results are then used to discuss the factorization of four point functions by applying the bootstrap approach. We also study the modular properties of the model. Although the Euclidean partition function is modular invariant, the characters on the Euclidean torus diverge and the regularization proposed in the literature removes information on the spectrum, so that the usual one to one map between characters and representations of rational models is lost. Reconsidering the characters defined on the Lorentzian torus and focusing on their structure as distributions, we obtain expressions that recover those properties. We then study their generalized modular properties and use them to discuss the relation between modular data and one point functions associated to symmetric D-branes, generalizing some results from Rational Conformal Field Theories in the particular cases of point like and dS2 branes, such as Cardy type solutions or Verlinde like formulas.

hep-th↗

arXiv2009

Fusion rules and four-point functions in the AdS3 WZNW model

We study the operator product expansion in the AdS$_3$ WZNW model. The OPE of primary fields and their spectral flow images is computed from the analytic continuation of the expressions in the H$_3^+$ WZNW model, adding spectral flow. We argue that the symmetries of the affine algebra require a truncation which establishes the closure of the fusion rules on the Hilbert space of the theory. Although the physical mechanism determining the decoupling is not completely understood, we present several consistency checks on the results. A preliminary analysis of factorization allows to obtain some properties of four-point functions involving fields in generic sectors of the theory, to verify that they agree with the spectral flow selection rules and to show that the truncation must be realized in physical amplitudes for consistency.

hep-th↗

arXiv2007

On supersymmetric $D6$-$\bar D 6$ systems with magnetic fields

We study systems of $D6$ and $\bar D 6$ branes with non zero world-volume magnetic fields in the weak coupling limit. We find two configurations for which the conditions for absence of tachyons in the spectra coincide exactly with those found in the low energy effective theory approach, for the systems to preserve 1/8 of the supersymmetries of the Type $IIA$ string theory vacuum. These conditions give rise to a four-parameter family of solutions in each case. We present further evidence of the stability of these systems by computing the lowest order interaction amplitude, verifying the no force condition as well as the supersymmetric character of the spectrum.

hep-th↗