Kac-Moody and Borcherds Symmetries of Six-Dimensional Chiral Supergravity

We investigate the conjectured infinite-dimensional hidden symmetries of six-dimensional chiral supergravity coupled to two vector multiplets and two tensor multiplets, which is known to possess the $F_{4,4}$ symmetry upon dimensional reduction to three spacetime dimensions. Two things are done. (i) First, we analyze the geodesic equations on the coset space $F_{4,4}^{++}/K(F_{4,4}^{++})$ using the level decomposition associated with the subalgebra $\mathfrak{gl}(5)\oplus \mathfrak{sl}(2)$ of $F_{4,4}^{++}$ and show their equivalence with the bosonic equations of motion of six-dimensional chiral supergravity up to the level where the dual graviton appears. In particular, the self-duality condition on the chiral $2$-form is automatically implemented in the sense that no dual potential appears for that $2$-form, in contradistinction with what occurs for the non chiral $p$-forms. (ii) Second, we describe the $p$-form hierarchy of the model in terms of its $V$-duality Borcherds superalgebra, of which we compute the Cartan matrix.Comment: 31 pages. v2: Error in section 6.3 corrected, Dynkin diagram now appears correctly, minor typo

Enhancement of hidden symmetries and Chern-Simons couplings

We study the role of Chern--Simons couplings for the appearance of enhanced symmetries of Cremmer--Julia type in various theories. It is shown explicitly that for generic values of the Chern--Simons coupling there is only a parabolic Lie subgroup of symmetries after reduction to three space-time dimensions but that this parabolic Lie group gets enhanced to the full and larger Cremmer--Julia Lie group of hidden symmetries if the coupling takes a specific value. This is heralded by an enhanced isotropy group of the metric on the scalar manifold. Examples of this phenomenon are discussed as well as the relation to supersymmetry. Our results are also connected with rigidity theorems of Borel-like algebras.Comment: To appear in the Proceedings of the 9th Workshop and School on "Quantum Field Theory and Hamiltonian Systems", 24-28 September 2014, Sinaia, Romani

Aspects of electric-magnetic dualities in maximal supergravity

This thesis is devoted to various aspects of electric-magnetic duality and its gravitational generalization, with an emphasis on the case of maximal supergravity. It is divided into three parts. In the first part, we review the the Cremmer-Julia "hidden" symmetries of maximal supergravity in various dimensions. Two new results are obtained: we prove that those symmetries appear if and only if the Chern-Simons coupling of the $D=11$ theory takes the value predicted by supersymmetry, and we obtain a manifestly $E_{7(7)}$-invariant formula for the entropy of non-extremal black holes in $D=4$, $N=8$ supergravity. The second part is motivated by supergravity gaugings. We examine through BRST methods the local deformations of non-minimally coupled scalars and abelian vector fields in four dimensions. We prove that they are all of the usual Yang-Mills type, i.e., correspond to the gauging of some rigid symmetries of the undeformed theory. We also show that other Lagragians considered in the literature, containing additional fields, do not allow for gaugings that cannot be reached starting from the usual Lagrangian. In the third part, we construct self-contained action principles for several self-dual free fields in six dimensions. These fields are motivated by two considerations: they allow for a geometric interpretation of the electric-magnetic duality symmetries of linearized gravity in four dimensions, and they also appear in the spectrum of the chiral $N=(4,0)$ and $N=(3,1)$ "exotic supergravities" in place of a metric. The free action and supersymmetry transformations for those theories are then explicitly constructed. We check that they reduce to linearized maximal supergravity in five dimensions, and also generalize previous works on linearized supergravity by other authors in which the graviton and its dual appear on the same footing at the level of the action.Comment: Ph.D. Thesis, Universit\'e Libre de Bruxelles. 139 pages + appendices. Based on arXiv:1505.07355, arXiv:1510.03582, arXiv:1612.02772, arXiv:1709.06014, arXiv:1711.07448, arXiv:1712.08126, arXiv:1804.06729 and arXiv:1804.1012

Higher spins from exotic dualisations

At the free level, a given massless field can be described by an infinite number of different potentials related to each other by dualities. In terms of Young tableaux, dualities replace any number of columns of height $h_i$ by columns of height $D-2-h_i$, where $D$ is the spacetime dimension: in particular, applying this operation to empty columns gives rise to potentials containing an arbitrary number of groups of $D-2$ extra antisymmetric indices. Using the method of parent actions, action principles including these potentials, but also extra fields, can be derived from the usual ones. In this paper, we revisit this off-shell duality and clarify the counting of degrees of freedom and the role of the extra fields. Among others, we consider the examples of the double dual graviton in $D=5$ and two cases, one topological and one dynamical, of exotic dualities leading to spin three fields in $D=3$.Comment: 31 pages. v2: typos corrected, published versio

Prepotentials for linearized supergravity

Linearized supergravity in arbitrary dimension is reformulated into a first order formalism which treats the graviton and its dual on the same footing at the level of the action. This generalizes previous work by other authors in two directions: 1) we work in arbitrary space-time dimension, and 2) the gravitino field and supersymmetry are also considered. This requires the construction of conformally invariant curvatures (the Cotton fields) for a family of mixed symmetry tensors and tensor-spinors, whose properties we prove (invariance; completeness; conformal Poincar\'e lemma). We use these geometric tools to solve the Hamiltonian constraints appearing in the first order formalism of the graviton and gravitino: the constraints are solved through the introduction of prepotentials enjoying (linearized) conformal invariance. These new variables (two tensor fields for the graviton, one tensor-spinor for the gravitino) are injected into the action and equations of motion, which take a geometrically simple form in terms of the Cotton tensor(-spinors) of the prepotentials. In particular, the equations of motion of the graviton are equivalent to twisted self-duality conditions. We express the supersymmetric transformations of the graviton and gravitino into each other in terms of the prepotentials. We also reproduce the dimensional reduction of supergravity within the prepotential formalism. Finally, our formulas in dimension five are recovered from the dimensional reduction of the already known prepotential formulation of the six-dimensional $\mathcal{N}=(4,0)$ maximally supersymmetric theory.Comment: v2: updated reference

Gravitational anomalies of fermionic higher-spin fields

Using the Atiyah-Singer index theorem, we formally compute gravitational anomalies for fermionic higher-spin fields in two, six and ten dimensions, as well as the U(1) mixed gauge-gravitational anomaly in four dimensions. In all cases, anomaly cancellations are found for an infinite tower of fields with alternating chiralities.Comment: 11 pages. v2: Comments and references added, published versio

Deformations of vector-scalar models

Abelian vector fields non-minimally coupled to uncharged scalar fields arise in many contexts. We investigate here through algebraic methods their consistent deformations ("gaugings"), i.e., the deformations that preserve the number (but not necessarily the form or the algebra) of the gauge symmetries. Infinitesimal consistent deformations are given by the BRST cohomology classes at ghost number zero. We parametrize explicitly these classes in terms of various types of global symmetries and corresponding Noether currents through the characteristic cohomology related to antifields and equations of motion. The analysis applies to all ghost numbers and not just ghost number zero. We also provide a systematic discussion of the linear and quadratic constraints on these parameters that follow from higher-order consistency. Our work is relevant to the gaugings of extended supergravities.Comment: v2: references added, typos corrected, minor changes for clarit

A note on the double dual graviton

The (free) graviton admits, in addition to the standard Pauli-Fierz description by means of a rank-two symmetric tensor, a description in which one dualizes the corresponding (2,2)-curvature tensor on one column to get a (D-2,2)-tensor, where D is the spacetime dimension. This tensor derives from a gauge field with mixed Yound symmetry (D-3,1) called the "dual graviton" field. The dual graviton field is related non-locally to the Pauli-Fierz field (even on-shell), in much the same way as a p-form potential and its dual (D-p-2)-form potential are related in the theory of an abelian p-form. Since the Pauli-Fierz field has a Young tableau with two columns (of one box each), one can contemplate a double dual description in which one dualizes on both columns and not just on one. The double dual curvature is now a (D-2,D-2)-tensor and derives from a gauge field with (D-3, D-3) mixed Young symmetry, the "double dual graviton" field. We show, however, that the double dual graviton field is algebraically and locally related to the original Pauli-Fierz field and, so, does not provide a truly new description of the graviton. From this point of view, it plays a very different role from the dual graviton field obtained through a single dualization. We also show that these equations can be obtained from a variational principle in which the variables to be varied in the action are (all) the components of the double-dual field as well as an auxiliary field with (2,1) Young symmetry. By gauge fixing the shift symmetries of this action principle, one recovers the Pauli-Fierz action. Our approach differs from the interesting approach based on parent actions and covers only the free, sourceless theory. Similar results are argued to hold for higher spin gauge fields

Homotopy Transfer and Effective Field Theory II: Strings and Double Field Theory

We continue our study of effective field theory via homotopy transfer of $L_\infty$-algebras, and apply it to tree-level non-Wilsonian effective actions of the kind discussed by Sen in which the modes integrated out are comparable in mass to the modes that are kept. We focus on the construction of effective actions for string states at fixed levels and in particular on the construction of weakly constrained double field theory. With these examples in mind, we discuss closed string theory on toroidal backgrounds and resolve some subtle issues involving vertex operators, including the proper form of cocycle factors and of the reflector state. This resolves outstanding issues concerning the construction of covariant closed string field theory on toroidal backgrounds. The weakly constrained double field theory is formally obtained from closed string field theory on a toroidal background by integrating out all but the doubly massless' states and homotopy transfer then gives a prescription for determining the theory's vertices and symmetries. We also discuss consistent truncation in the context of homotopy transfer.Comment: 53 pages. v2: References adde