arXiv subjects

Olaf Hohm

Publications and source records attributed to Olaf Hohm.

At least 55 records · Page 3Linked to original sources

arXiv2020

Green-Schwarz Mechanism for String Dualities

We determine the complete spacetime action to first order in $α'$ for the massless fields of bosonic string theory compactified on a $d$-dimensional torus. A fully systematic procedure is developed that brings the action into a minimal form in which all fields apart from the metric enter only with first-order derivatives. T-duality implies that this action must have a global $\mathrm{O}(d,d,\mathbb{R})$ symmetry, and we show that this requires a Green-Schwarz type mechanism for $α'$-deformed $\mathrm{O}(d,d,\mathbb{R})$ transformations. In terms of a frame formalism with ${\rm GL}(d)\times {\rm GL}(d)$ gauge symmetry this amounts to a modification of the three-form curvature by a Chern-Simons term for composite gauge fields.

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arXiv2019

Duality Hierarchies and Differential Graded Lie Algebras

The gauge theories underlying gauged supergravity and exceptional field theory are based on tensor hierarchies: generalizations of Yang-Mills theory utilizing algebraic structures that generalize Lie algebras and, as a consequence, require higher-form gauge fields. Recently, we proposed that the algebraic structure allowing for consistent tensor hierarchies is axiomatized by `infinity-enhanced Leibniz algebras' defined on graded vector spaces generalizing Leibniz algebras. It was subsequently shown that, upon appending additional vector spaces, this structure can be reinterpreted as a differential graded Lie algebra. We use this observation to streamline the construction of general tensor hierarchies, and we formulate dynamics in terms of a hierarchy of first-order duality relations, including scalar fields with a potential.

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arXiv2019

The many facets of exceptional field theory

Exceptional field theories are the manifestly duality covariant formulations of the target space theories of string/M-theory in the low-energy limit (supergravity) or for certain truncations. These theories feature a rich system of sub-theories, corresponding to different consistent truncations. We review the structure of exceptional field theory and elaborate on various potential applications. In particular, we discuss how exceptional field theories capture some of the the magic supergravity triangles, Hull's $*$-theories related to timelike dualities, as well as the generalized supergravities related to integrable deformations of AdS/CFT.

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arXiv2019

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.

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arXiv2019

The dual graviton in duality covariant theories

We review (and elaborate on) the `dual graviton problem' in the context of duality covariant formulations of M-theory (exceptional field theories). These theories require fields that are interpreted as components of the dual graviton in order to build complete multiplets under the exceptional groups E$_{d(d)}$, $d=2,\ldots, 9$. Circumventing no-go arguments, consistent theories for such fields have been constructed by incorporating additional covariant compensator fields. The latter fields are needed for gauge invariance but also for on-shell equivalence with $D=11$ and type IIB supergravity. Moreover, these fields play a non-trivial role in generalized Scherk-Schwarz compactifications, as for instance in consistent Kaluza-Klein truncation on AdS$_4\times {\rm S}^7$.

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arXiv2019

Non-perturbative de Sitter vacua via $α'$ corrections

The higher-derivative $α'$ corrections consistent with $O(d,d)$ duality invariance can be completely classified for cosmological, purely time-dependent backgrounds. This result is used to show that there are duality invariant theories featuring string-frame de Sitter vacua as solutions that are non-perturbative in $α'$, thus suggesting that classical string theory may realize de Sitter solutions in an unexpected fashion.

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arXiv2019

Reviving 3D ${\cal N}=8$ superconformal field theories

We present a Lagrangian formulation for ${\cal N}=8$ superconformal field theories in three spacetime dimensions that is general enough to encompass infinite-dimensional gauge algebras that generally go beyond Lie algebras. To this end we employ Chern-Simons theories based on Leibniz algebras, which give rise to L$_{\infty}$ algebras and are defined on the dual space $\frak{g}^*$ of a Lie algebra $\frak{g}$ by means of an embedding tensor map $\vartheta :\frak{g}^*\rightarrow \frak{g}$. We show that for the Lie algebra $\frak{sdiff}_3$ of volume-preserving diffeomorphisms on a 3-manifold there is a natural embedding tensor defining a Leibniz algebra on the space of one-forms. Specifically, we show that the cotangent bundle to any 3-manifold with a volume-form carries the structure of a (generalized) Courant algebroid. The resulting ${\cal N}=8$ superconformal field theories are shown to be equivalent to Bandos-Townsend theories. We show that the theory based on $S^3$ is an infinite-dimensional generalization of the Bagger-Lambert-Gustavsson model that in turn is a consistent truncation of the full theory. We also review a Scherk-Schwarz reduction on $S^2\times S^1$, which gives the super-Yang-Mills theory with gauge algebra $\frak{sdiff}_2$, and we construct massive deformations.

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arXiv2019

Higher Gauge Structures in Double and Exceptional Field Theory

We review the higher gauge symmetries in double and exceptional field theory from the viewpoint of an embedding tensor construction. This is based on a (typically infinite-dimensional) Lie algebra $\frak{g}$ and a choice of representation $R$. The embedding tensor is a map from the representation space $R$ into $\frak{g}$ satisfying a compatibility condition (`quadratic constraint'). The Lie algebra structure on $\frak{g}$ is transported to a Leibniz--Loday algebra on $R$, which in turn gives rise to an $L_{\infty}$-structure. We review how the gauge structures of double and exceptional field theory fit into this framework.

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arXiv2019

Leibniz-Chern-Simons Theory and Phases of Exceptional Field Theory

We discuss a generalization of Chern-Simons theory in three dimensions based on Leibniz (or Loday) algebras, which are generalizations of Lie algebras. Special cases of such theories appear in gauged supergravity, where the Leibniz algebra is defined in terms of the global (Lie) symmetry algebra of the ungauged limit and an embedding tensor. We show that the Leibniz algebra of generalized diffeomorphisms in exceptional field theory can similarly be obtained from a Lie algebra that describes the enhanced symmetry of an `ungauged phase' of the theory. Moreover, we show that a `topological phase' of ${\rm E}_{8(8)}$ exceptional field theory can be interpreted as a Chern-Simons theory for an algebra unifying the three-dimensional Poincaré algebra and the Leibniz algebra of ${\rm E}_{8(8)}$ generalized diffeomorphisms.

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arXiv2018

Constructions of L$_{\infty}$ algebras and their field theory realizations

We construct L$_{\infty}$ 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$_{\infty}$ algebra on a graded vector space of twice the dimension, with the 3-bracket being related to the Jacobiator. While these L$_{\infty}$ algebras always exist, they generally do not realize a non-trivial symmetry in a field theory. In order to define L$_{\infty}$ algebras with genuine field theory realizations, we 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$_{\infty}$ 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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arXiv2018

On Background Independence in String Theory

I discuss various aspects of background independence in the context of string theory, for which so far we have no manifestly background independent formulation. After reviewing the role of background independence in classical Einstein gravity, I discuss recent results implying that there is a conflict in string theory between manifest background independence and manifest duality invariance when higher-derivative corrections are included. The resolution of this conflict requires the introduction of new gauge degrees of freedom together with an enlarged gauge symmetry. This suggests more generally that a manifestly background independent and duality invariant formulation of string theory requires significantly enhanced gauge symmetries.

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arXiv2017

O(d+1,d+1) enhanced double field theory

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 $T^d$. 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 $D=6$, ${\cal N}=(1,1)$ and $D=6$, ${\cal N}=(2,0)$ supergravity on AdS$_3\times \mathbb{S}^3$.

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arXiv2017

Background Independent Double Field Theory at Order $α'$: Metric vs. Frame-like Geometry

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 $GL(D)\times GL(D)$ 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 ${\cal E}$, the sum of metric and $b$-field. The transformations of ${\cal E}$ 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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arXiv2017

On Background Independence and Duality Invariance in String Theory

Closed string theory exhibits an O(D,D) duality symmetry on tori, which in double field theory is manifest before compactification. I prove that to first order in $α'$ there is no manifestly background independent and duality invariant formulation of bosonic string theory in terms of metric, b-field and dilaton. To this end I use O(D,D) invariant second order perturbation theory around flat space to show that the unique background independent candidate expression for the gauge algebra at order $α'$ is inconsistent with the Jacobi identity. A background independent formulation exists instead for frame variables subject to $α'$-deformed frame transformations (generalized Green-Schwarz transformations). Potential applications for curved backgrounds, as in cosmology, are discussed.

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arXiv2017

$L_{\infty}$ Algebras and Field Theory

We review and develop the general properties of $L_\infty$ algebras focusing on the gauge structure of the associated field theories. Motivated by the $L_\infty$ 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 $L_\infty$ 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 $L_\infty$ 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 $L_\infty$ algebra for the interacting theory. The analysis suggests that $L_\infty$ algebras provide a classification of perturbative gauge invariant classical field theories.

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arXiv2017

Exotic Dual of Type II Double Field Theory

We perform an exotic dualization of the Ramond-Ramond fields in type II double field theory, in which they are encoded in a Majorana-Weyl spinor of O(D,D). Starting from a first-order master action, the dual theory in terms of a tensor-spinor of O(D,D) is determined. This tensor-spinor is subject to an exotic version of the (self-)duality constraint needed for a democratic formulation. We show that in components, reducing O(D,D) to GL(D), one obtains the expected exotically dual theory in terms of mixed Young tableaux fields. To this end, we generalize exotic dualizations to self-dual fields, such as the 4-form in type IIB string theory.

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arXiv2016

On the curious spectrum of duality invariant higher-derivative gravity

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 $α'\rightarrow \infty$ 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.

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arXiv2016

Dual Double Field Theory

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.

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