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David Osten

Publications and source records attributed to David Osten.

18 recordsLinked to original sources

Tensor hierarchy from deformation quantisation

We show that a formal deformation quantisation of degree-2 differential graded symplectic (QP) manifolds gives rise to the complete classical kinematics and dynamics of NS-NS supergravity, or, equivalently, its duality-covariant formulation as double field theory (DFT). Our construction extends the standard tensor hierarchy, encoding gauge parameters and their redundancies, to a complex encoding the physical fields, field strengths, and Bianchi identities. We present two realisations of such a complex: 1) a differential graded Lie algebra built from the algebra of functions on the QP-manifold; 2) a cochain complex that reproduces the tensor hierarchy representations conjectured in the literature and can be interpreted as a classical BV complex of the linearised theory. The deformation that gives rise to the dilaton comes from a normal-ordered graded Moyal--Weyl star product. This naturally extends the duality structure group from $\mathrm{O}(D,D)$ to $\mathrm{O}(D,D)\times\mathbb{R}^+$. Finally, our framework provides a direct route to constructing the DFT action via local double Lorentz invariance, and offers a transparent algebraic foundation for curvature tensors in generalised Cartan geometry.

hep-th

Duality-covariant particles and exotic branes

In this paper we construct duality-covariant worldvolume dynamics of particles and branes. We extend known actions and phase space formulations to include the hidden $E_8$ symmetry of 11D supergravity, analogous to the Ehlers symmetry of 4D gravity. Making the worldvolume theory manifestly duality-covariant requires the ancillary structure of $E_8$ exceptional field theory to be taken into account. For zero-branes, we propose an enlarged worldline model with a coadjoint orbit term to encode this. More generally, we propose worldvolume theories for arbitrary exotic branes in a way that generalises the known gauged sigma model of the Kaluza-Klein monopole. These are natural in the duality-covariant Hamiltonian formulation employed here. We discuss the case of zero-branes in eleven dimensions as an illustrative example.

hep-th

Generalised Cartan Geometry

This talk introduces a Cartan-geometric framework for generalised geometries governed by a differential graded Lie algebra. In contrast to ordinary Cartan geometry, the tangent bundle is extended and qu both a global duality group and a local gauge group. This framework provides a systematic construction of generalised connections and their torsion and curvature tensors for generic generalised geometries. We also review the realisation of these algebraic structures on the phase space of branes in M-theory.

hep-th

Gauged Extended Field Theory and Generalised Cartan Geometry

Cartan geometry provides a unifying algebraic construction of curvature and torsion, based on an underlying model Lie algebra -- a viewpoint that can be extended naturally to the higher algebraic structures underlying supergravity. We present a Cartan-geometric framework for generalised geometries governed by a differential graded Lie algebra, extending previous results. The extended tangent bundle admits the action of both a global duality group $\mathcal{G}$ and a local gauge group $H$. This algebraic structure is implemented via a brane current algebra -- the phase space Poisson structure of $p$-branes. Within this Cartan-inspired framework, we define a hierarchy of generalised connections and compute their linearised torsion and curvature tensors, including the higher curvatures required by the tensor hierarchy. This provides a systematic construction of curvature and torsion tensors in generic generalised geometries.

hep-th

The Manakov-Zakharov-Ward model as an integrable decoupling limit of the membrane

A novel decoupling limit of the membrane is proposed, leading to the $(1+2)$-dimensional classically integrable model originally introduced by Manakov, Zakharov, and Ward. This limit is the large-wrapping regime of a membrane propagating toy background of the form $\mathbb{R}_t \times T^2 \times G$ subject to scaling limit, where $G$ is a Lie group and the geometry is supported by a four-form flux. Such toy backgrounds can arise from consistent eleven-dimensional supergravity solutions, exemplified by the uplift of the pure NSNS AdS$_3 \times$ S$^3 \times$ T$^4$ background. The scaling limit can be interpreted as similtaneous small tension and non- or hyper-relativistic limit.

hep-th

Integrable deformations of dimensionally reduced gravity

Dimensional reduction of gravity theories to $D=2$ along commuting Killing isometries is well-known to be classically integrable. The resulting system typically features a coset $\sigma$-model coupled to a dilaton and a scale factor of the dimensional reduction. In this article, we construct two families of deformations of dimensionally reduced gravity that preserve the Lax integrable structure. The first family is an extension of the Auxiliary Field Deformation recently introduced by Ferko and Smith, while the second family consists in the embedding of the Yang-Baxter $\sigma$-model into $D=2$ dimensionally reduced gravity. For both deformations we construct flat Lax representations. The Auxiliary Field Deformation, in particular, preserves the rich algebraic structure underlying the undeformed model and, leaving the canonical structure of the Lax connection's spatial components essentially unchanged, allows us to prove its integrability also in the Hamiltonian sense.

hep-th

Duality covariant curvatures for the heterotic string

Duality covariant curvature and torsion tensors in double field theory/generalized geometry are central in analyzing consistent truncations, generalized dualities, and related integrable $\sigma$-models. They are constructed systematically with the help of a larger, auxiliary space in a procedure inspired by Cartan geometry originally proposed by Pol\'a\v{c}ek and Siegel for bosonic strings. It pivots around a maximally isotropic group that captures the generalized structure group of the physical space. We show how dropping the isotropy condition on this group allows us to describe heterotic/type I strings. As an immediate application, we construct a new family of heterotic backgrounds that interpolates between the two-dimensional cigar and trumpet backgrounds.

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Integrable auxiliary field deformations of coset models

We prove the existence of a family of integrable deformations of $\mathbb{Z}_N$-coset models in two dimensions. Our approach uses and generalises the method of auxiliary fields that was recently introduced for the principal chiral model by Ferko and Smith.

hep-th

Current Algebra and Generalised Cartan Geometry

This article shows that the approach to generalised curvature and torsion pioneered by Polacek and Siegel [1] is a generalisation of Cartan Geometry -- rendering latter natural from the point of view of O(d,d)-generalised geometry. We present this approach in the generalised metric formalism and show that almost all parts of the additional higher generalised tensors appearing in this approach correspond to covariant derivatives of the generalised Riemann tensor. As an application, we use this framework to phrase sigma model dynamics in an explicitly covariant way -- both under generalised diffeomorphisms and local gauge transformations.

hep-th

Non-Relativistic Limits of Bosonic and Heterotic Double Field Theory

The known stringy non-relativistic (NR) limit of the universal NS-NS sector of supergravity has a finite Lagrangian due to non-trivial cancellations of divergent parts coming from the metric and the $B$-field. We demonstrate that in Double Field Theory (DFT) and generalised geometry these cancellations already happen at the level of the generalised metric, which is convergent in the limit $c \rightarrow \infty$, implying that the NR limit can be imposed before solving the strong constraint. We present the $c$-expansion of the generalised metric, which reproduces the Non-Riemannian formulation of DFT at the (finite) leading order, and the $c$-expansion of the generalised frame, which contains divergences. We also extend this approach to the non-Abelian gauge field of Heterotic DFT assuming a convergent expansion for the O$(D,D+n)$ generalised metric. From this proposal, we derive a novel $c$-expansion for the bosonic part of the heterotic supergravity which is, by construction, compatible with O$(D,D)$-symmetry.

hep-th

On the universal exceptional structure of world-volume theories in string and M-theory

A universal structure of world-volume theories of half-BPS branes in string and M-theory in terms of exceptional generalised geometry is observed. Previous constructions are extended in two ways: from internal $d$-dimensional space to full 11- or 10-dimensional spacetimes, by coupling to the tensor hierarchy gauge fields, and from $E_{d(d)}$ with $d\leq 6$ to $E_{7(7)}$ and $E_{8(8)}$. This is done by a clarification of the role of the tensor hierarchy and its end in the context of brane world-volume theories. The exceptional structure of the gauged $\sigma$-model of the Kaluza-Klein monopole is provided as a new example.

hep-th

A heterotic integrable deformation of the principal chiral model

A novel classically integrable model is proposed. It is a deformation of the two-dimensional principal chiral model, embedded into a heterotic $\sigma$-model, by a particular heterotic gauge field. This is inspired by the bosonic part of the heterotic $\sigma$-model and its recent Hamiltonian formulation in terms of O$(d,d+n)$-generalised geometry by Hatsuda, Mori, Sasaki and Yata. Classical integrability is shown by construction of a Lax pair and a classical $\mathcal{R}$-matrix. Latter is almost of the canonical form with twist function and solves the classical Yang-Baxter equation.

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On exceptional QP-manifolds

The connection between two recent descriptions of tensor hierarchies - namely, infinity-enhanced Leibniz algebroids, given by Bonezzi & Hohm and Lavau & Palmkvist, the p-brane QP-manifolds constructed by Arvanitakis - is made precise. This is done by presenting a duality-covariant version of latter. The construction is based on the QP-manifold $T^\star[n]T[1]M \times \mathcal{H}[n]$, where $M$ corresponds to the internal manifold of a supergravity compactification and $\mathcal{H}[n]$ to a degree-shifted version of the infinity-enhanced Leibniz algebroid. Imposing that the canonical Q-structure on $T^\star[n] T[1] M$ is the derivative operator on $\mathcal{H}$ leads to a set of constraints. Solutions to these constraints correspond to $\frac{1}{2}$-BPS p-branes, suggesting that this is a new incarnation of a brane scan. Reduction w.r.t. to these constraints reproduces the known p-brane QP-manifolds. This is shown explicitly for the SL(3)$\times$SL(2)- and SL(5)-theories. Furthermore, this setting is used to speculate about exceptional 'extended spaces' and QP-manifolds associated to Leibniz algebras. A proposal is made to realise differential graded manifolds associated to Leibniz algebras as non-Poisson subspaces (i.e. not Poisson reductions) of QP-manifolds similar to the above. Two examples for this proposal are discussed: generalised fluxes (including the dilaton flux) of O(d,d) and the 3-bracket flux for the SL(5)-theory.

hep-th

Lax pairs for new $\mathbb{Z}_N$-symmetric coset $\sigma$-models and their Yang-Baxter deformations

Two-dimensional $\sigma$-models with $\mathbb{Z}_N$-symmetric homogeneous target spaces have been shown to be classically integrable when introducing WZ-terms in a particular way. This article continues the search for new models of this type now allowing some kinetic terms to be absent, analogously to the Green-Schwarz superstring $\sigma$-model on $\mathbb{Z}_4$-symmetric homogeneous spaces. A list of such integrable $\mathbb{Z}_N$-symmetric (super)coset $\sigma$-models for $N \leq 6$ and their Lax pairs is presented. For arbitrary $N$, a big class of integrable models is constructed that includes both the known pure spinor and Green-Schwarz superstring on $\mathbb{Z}_4$-symmetric cosets. Integrable Yang-Baxter deformations of this class of $\mathbb{Z}_N$-symmetric (super)coset $\sigma$-models can be constructed in same way as in the known $\mathbb{Z}_2$- or $\mathbb{Z}_4$-cases. Deformations based on solutions of the modified classical Yang-Baxter equation, the so-called $\eta$-deformation, require deformation of the constants defining the Lagrangian and the corresponding Lax pair. Homogeneous Yang-Baxter deformations (i.e. those based on solutions to the classical Yang-Baxter equation) leave the equations of motion and consequently the Lax pair invariant and are expected to be classically equivalent to the undeformed model. As an example, the relationship between $\mathbb{Z}_3$-symmetric homogeneous spaces and nearly (para-)K\"ahler geometries is revisited. Confirming existing literature it is shown that the integrable choice of WZ-term in the $\mathbb{Z}_3$-symmetric coset $\sigma$-model associated to a nearly K\"ahler background gives an imaginary contribution to the action.

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Currents, charges and algebras in exceptional generalised geometry

A classical $E_{d(d)}$-invariant Hamiltonian formulation of world-volume theories of half-BPS p-branes in type IIb and eleven-dimensional supergravity is proposed, extending known results to $d \leq 6$. It consists of a Hamiltonian, characterised by a generalised metric, and a current algebra constructed s.t. it reproduces the $E_{d(d)}$ generalised Lie derivative. $E_{d(d)}$-covariance necessitates the introduction of so-called charges, specifying the type of p-brane and the choice of section. For p>2, currents of p-branes are generically non-geometric due to the imposition of U-duality, e.g. the M5-currents contain coordinates associated to the M2-momentum. A derivation of the $E_{d(d)}$-invariant current algebra from a canonical Poisson structure is in general not possible. At most, one can derive a current algebra associated to para-Hermitian exceptional geometry. The membrane in the SL(5)-theory is studied in detail. It is shown that in a generalised frame the current algebra is twisted by the generalised fluxes. As a consistency check, the double dimensional reduction from membranes in M-theory to strings in type IIa string theory is performed. Many features generalise to p-branes in SL(p+3) generalised geometries that form building blocks for the $E_{d(d)}$-invariant currents.

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On current algebras, generalised fluxes and non-geometry

A Hamiltonian formulation of the classical world-sheet theory in a generic, geometric or non-geometric, NSNS background is proposed. The essence of this formulation is a deformed current algebra, which is solely characterised by the generalised fluxes describing such a background. The construction extends to backgrounds for which there is no Lagrangian description -- namely magnetically charged backgrounds or those violating the strong constraint of double field theory -- at the cost of violating the Jacobi identity of the current algebra. The known non-commutative and non-associative interpretation of non-geometric flux backgrounds is reproduced by means of the deformed current algebra. Furthermore, the provided framework is used to suggest a generalisation of Poisson-Lie $T$-duality to generic models with constant generalised fluxes. As a side note, the relation between Lie and Courant algebroid structures of the string current algebra is clarified.

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Generalised fluxes, Yang-Baxter deformations and the O(d,d) structure of non-abelian T-duality

Based on the construction of Poisson-Lie T-dual $\sigma$-models from a common parent action we study a candidate for the non-abelian respectively Poisson-Lie T-duality group. This group generalises the well-known abelian T-duality group O(d,d) and we explore some of its subgroups, namely factorised dualities, B- and $\beta$-shifts. The corresponding duality transformed $\sigma$-models are constructed and interpreted as generalised (non-geometric) flux backgrounds. We also comment on generalisations of results and techniques known from abelian T-duality. This includes the Lie algebra cohomology interpretation of the corresponding non-geometric flux backgrounds, remarks on a double field theory based on non-abelian T-duality and an application to the investigation of Yang-Baxter deformations. This will show that homogeneously Yang-Baxter deformed $\sigma$-models are exactly the non-abelian T-duality $\beta$-shifts when applied to principal chiral models.

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Abelian Yang-Baxter Deformations and TsT transformations

We prove that abelian Yang-Baxter deformations of superstring coset sigma models are equivalent to sequences of commuting TsT transformations, meaning T dualities and coordinate shifts. Our results extend also to fermionic deformations and fermionic T duality, and naturally lead to a TsT subgroup of the superduality group OSp(d_b,d_b|2d_f). In cases like AdS_5 x S^5, fermionic deformations necessarily lead to complex models. As an illustration of inequivalent deformations, we give all six abelian deformations of AdS_3. We comment on the possible dual field theory interpretation of these (super-)TsT models.

hep-th