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Chris D. A. Blair

Publications and source records attributed to Chris D. A. Blair.

At least 19 recordsLinked to original sources
arXiv2026

Carroll Geometry Meets De Sitter Space via Holography

We explain how to relate the ideas of Carroll geometry, matrix theory on instantonic objects, and infinite boost limits of M-theory. Based on these new insights, we explore the implications for possible holographic constructions involving a de Sitter or flat space bulk. We show that Carroll-like (including particle Carroll) geometry in a hypothetical de Sitter holography mirrors the recently realized important role played by Galilei-like geometry in matrix theory and the AdS/CFT correspondence. This also allows us to generate examples of holography with a Carroll-like bulk.

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arXiv2025

Dual Non-Lorentzian Backgrounds for Matrix Theories

We study properties of non-Lorentzian geometries arising from BPS decoupling limits of string theory that are central to matrix theory and the AdS/CFT correspondence. We focus on duality transformations between ten-dimensional non-Lorentzian geometries coupled to matrix theory on D-branes. We demonstrate that T- and S-duality transformations exhibit novel asymmetric properties: depending not only on the choice of transformation but also on the value of the background fields, the codimension of the foliation structure of the dual non-Lorentzian background may be different or the same. This duality asymmetry underlies features observed in the study of non-commutativity and Morita equivalence in matrix and gauge theory. Finally, we show how the holographic correspondence involving non-commutative Yang-Mills fits into our framework, from which we further obtain novel holographic examples with non-Lorentzian bulk geometries.

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arXiv2025

Supersymmetric solutions of non-relativistic 11-dimensional supergravity

Eleven-dimensional supergravity has a non-relativistic variant obtained by taking a limit associated with the M2 brane. Consistency of this non-relativistic supergravity requires constraints. There is one choice of constraints which keeps the maximal amount of supersymmetry transformations, and another which only keeps half. I discuss supersymmetric solutions of this theory, based on limits of the M2 and M5 solutions. These limits involve either a scaling of the number of branes or a smearing in certain directions, and have been argued to produce non-Lorentzian bulk geometries appearing in novel versions of the AdS/CFT correspondence. I show that the scaled solutions are solutions of the maximally supersymmetric version of the non-relativistic supergravity, while the smeared solutions only give solutions of the half-maximally supersymmetric version. I show these solutions are all supersymmetric by solving the Killing spinor equations, and discuss usual and unusual forms of supersymmetry enhancement. I also discuss a simple supersymmetric AdS_3 background, and point out that the BTZ black hole is a solution of non-relativistic 11-dimensional supergravity.

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arXiv2025

The surprising structure of non-relativistic 11-dimensional supergravity

We study a non-relativistic limit of 11-dimensional supergravity. This limit leads to a theory with an underlying membrane Newton-Cartan geometry. Consistency of the non-relativistic limit requires the imposition of constraints, requiring that certain bosonic and fermionic torsions and curvatures vanish. We investigate the implications of two versions of these constraints. In one version, we keep only 16 supersymmetry transformations, leading to a simple (purely bosonic) constraint structure but an unusual realisation of the supersymmetry algebra which does not close into diffeomorphisms. In the other, we keep all 32 supersymmetry transformations. This requires a complicated sequence of bosonic and fermionic constraints, eventually involving three derivatives of bosonic fields. We argue, with a linearised calculation, that this sequence of constraints terminates. Furthermore, we show that there exists a family of supersymmetric solutions satisfying these constraints, containing the non-relativistic limit of the M2 supergravity solution recently obtained by Lambert and Smith as a background relevant for non-relativistic holography.

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arXiv2025

Matrix Theory Reloaded: A BPS Road to Holography

We revisit the decoupling limits that lead to matrix theories on D-branes. We highlight the BPS nature of these limits, in which the target space geometry becomes non-Lorentzian and wrapped D-branes experience instantaneous gravitational forces. Applied to curved D-brane geometries, we show that a single BPS decoupling limit induces the bulk near-horizon limit leading to AdS/CFT. By consecutively applying two such limits, we systematically generate further examples of holography, including novel versions with non-Lorentzian bulk geometry. Uplifted to M-theory, we are led to a unified framework where each BPS decoupling limit corresponds to a Discrete Light Cone Quantisation (DLCQ). We conjecture that a DLCQ${}^n$/DLCQ${}^{m}$ correspondence, with $m>n$, captures the notion of holography in string theory. In particular, AdS${}_5$/CFT${}_4$ can be viewed as an example of DLCQ${}^0$/DLCQ${}^{1}$, with the extra DLCQ on the field theory side corresponding to the near-horizon limit in the bulk geometry. We further show that undoing these BPS decoupling limits can be viewed as deformations of matrix theories. We explain how these deformations are related to the $T\bar{T}$ deformation in two dimensions. In the context of holography, this allows us to view the ten-dimensional near-horizon brane geometry as an intrinsic deformation of the flat non-Lorentzian geometry that arises asymptotically. In field theoretic terms, these generalisations lead to $T\bar{T}$-like flow equations for the D$p$-brane DBI action.

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arXiv2024

The Geometry, Branes and Applications of Exceptional Field Theory

This is a review of exceptional field theory: a generalisation of Kaluza-Klein theory that unifies the metric and $p$-form gauge field degrees of freedom of supergravity into a generalised or extended geometry, whose additional coordinates may be viewed as conjugate to brane winding modes. This unifies the maximal supergravities, treating their previously-hidden exceptional Lie symmetries as a fundamental geometric symmetry. Duality orbits of solutions simplify into single objects, that in many cases have simple geometric interpretations, for instance as wave or monopole-type solutions. It also provides a route to explore exotic or non-geometric aspects of M-theory, such as exotic branes, U-folds, and more novel sorts of non-Riemannian spaces.

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arXiv2024

Unification of Decoupling Limits in String and M-theory

We study and extend the duality web unifying different decoupling limits of type II superstring theories and M-theory. We systematically build connections to different corners, such as Matrix theories, nonrelativistic string and M-theory, tensionless (and ambitwistor) string theory, Carrollian string theory, and Spin Matrix limits of AdS/CFT. We discuss target space, worldsheet, and worldvolume aspects of these limits in arbitrary curved backgrounds.

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arXiv2024

Infinite and finite consistent truncations on deformed generalised parallelisations

Given a manifold $\mathbb{M}$ admitting a maximally supersymmetric consistent truncation, we show how to formulate new consistent truncations by restricting to a set of Kaluza-Klein modes on $\mathbb{M}$ invariant under some subgroup of the group of isometries of $\mathbb{M}$. These truncations may involve either finite or infinite sets of modes. We provide their global description using exceptional generalised geometry to construct a `deformed' generalised parallelisation starting with that on $\mathbb{M}$. This allows us to explicitly embed known consistent truncations directly into exceptional generalised geometry/exceptional field theory, and to obtain the equations governing situations where the consistent truncation retains an infinite tower of modes.

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arXiv2023

A non-relativistic limit of M-theory and 11-dimensional membrane Newton-Cartan geometry

We consider a non-relativistic limit of the bosonic sector of eleven-dimensional supergravity, leading to a theory based on a covariant `membrane Newton-Cartan' (MNC) geometry. The local tangent space is split into three `longitudinal' and eight `transverse' directions, related only by Galilean rather than Lorentzian symmetries. This generalises the ten-dimensional stringy Newton-Cartan (SNC) theory. In order to obtain a finite limit, the field strength of the eleven-dimensional four-form is required to obey a transverse self-duality constraint, ultimately due to the presence of the Chern-Simons term in eleven dimensions. The finite action then gives a set of equations that is invariant under longitudinal and transverse rotations, Galilean boosts and local dilatations. We supplement these equations with an extra Poisson equation, coming from the subleading action. Reduction along a longitudinal direction gives the known SNC theory with the addition of RR gauge fields, while reducing along a transverse direction yields a new non-relativistic theory associated to D2 branes. We further show that the MNC theory can be embedded in the U-duality symmetric formulation of exceptional field theory, demonstrating that it shares the same exceptional Lie algebraic symmetries as the relativistic supergravity, and providing an alternative derivation of the extra Poisson equation.

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arXiv2022

Generalised U-dual solutions via ISO(7) gauged supergravity

We study a solution generating technique in supergravity which can be viewed as a generalised version of U-duality, taking solutions of type IIA supergravity on a 6-sphere with RR flux to new solutions of 11-dimensional supergravity. The new solutions are characterised by an underlying 6-algebra structure. Our construction provides an 11-dimensional uplift of four-dimensional ISO(7) gauged supergravity, using $E_7$ exceptional geometry techniques. We focus on an example where we start with the D2 solution in type IIA supergravity and construct a new $\tfrac12$-BPS 11-dimensional solution.

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arXiv2022

Non-isometric U-dualities

I study generalisations of U-duality transformations which do not rely on the existence of isometries. I start by providing more details of a recently proposed generalised U-duality map between solutions of type IIA supergravity of the form $\text{M}_7 \times \text{S}^3$, with NSNS flux, and solutions of 11-dimensional supergravity, in which the three-sphere is replaced by a four-dimensional geometry which encodes three-algebra structure constants. I then show that when $\text{M}_7$ admits two abelian isometries, TsT deformations on the IIA side become six-vector deformations in the 11-dimensional setting. These six-vector deformations involve an action of $\mathrm{E}_{6(6)}$ on both isometric and non-isometric directions. I discuss the algebraic interpretation of these deformations, and compare and contrast them with (generalised) Yang-Baxter deformations in supergravity.

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arXiv2022

Generalised U-dual solutions in supergravity

We discuss the notion of generalised U-duality as a solution generating technique in supergravity. We demonstrate a method to take solutions of type IIA supergravity on a 3-sphere, with NSNS flux, to new solutions of 11-dimensional supergravity, using exceptional geometry techniques. These new solutions are characterised by an underlying 3-algebra structure, and generalise features of solutions obtained by non-abelian T-duality, which involve an underlying ordinary Lie algebra. We focus on an example where we start with the pp-F1-NS5 solution in type IIA supergravity. We discuss the properties of our resulting new solution, including the possibility of viewing it globally as a U-fold, and its M2 and M5 brane charges. In the extremal case, the new solution admits an AdS${}_3$ limit, which falls into a recently constructed class of M-theory AdS$_{3}$ backgrounds -- this provides a global completion of our solution with a well-defined holographic dual, similar to the global completions of non-abelian T-dual solutions. Our full solution is a 6-vector deformation of this AdS${}_3$ limit. We also explicitly solve the Killing spinor equation in the AdS${}_3$ limit, finding a $\frac{1}{2}$-BPS solution.

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arXiv2022

Doubled space and extended supersymmetry

The doubled formulation of the worldsheet provides a description of string theory in which T-duality is promoted to a manifest symmetry. Here we extend this approach to $\mathcal{N}=(2,2)$ superspace providing a doubled formulation for bi-Hermitian/generalised Kähler target spaces. The theory is described by a single function, a doubled-generalised Kähler potential, supplemented with a manifestly $\mathcal{N}=(2,2)$ constraint. Several examples serve to illustrate this construction, including a discussion of the $\mathcal{N}=(2,2)$ description of T-folds.

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arXiv2021

A QP perspective on topology change in Poisson-Lie T-duality

We describe topological T-duality and Poisson-Lie T-duality in terms of QP (differential graded symplectic) manifolds and their canonical transformations. Duality is mediated by a QP-manifold on doubled non-abelian "correspondence" space, from which we can perform mutually dual symplectic reductions, where certain canonical transformations play a vital role. In the presence of spectator coordinates, we show how the introduction of "bibundle" structure on correspondence space realises changes in the global fibration structure under Poisson-Lie duality. Our approach can be directly translated to the worldsheet to derive dual string current algebras. Finally, the canonical transformations appearing in our reduction procedure naturally suggest a Fourier-Mukai integral transformation for Poisson-Lie T-duality.

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arXiv2021

Non-Riemannian isometries from double field theory

We explore the notion of isometries in non-Riemannian geometries. Such geometries include and generalise the backgrounds of non-relativistic string theory, and they can be naturally described using the formalism of double field theory. Adopting this approach, we first solve the corresponding Killing equations for constant flat non-Riemannian backgrounds and show that they admit an infinite-dimensional algebra of isometries which includes a particular type of supertranslations. These symmetries correspond to known worldsheet Noether symmetries of the Gomis-Ooguri non-relativistic string, which we now interpret as isometries of its non-Riemannian doubled background. We further consider the extension to supersymmetric double field theory and show that the corresponding Killing spinors can depend arbitrarily on the non-Riemannian directions, leading to "supersupersymmetries" that square to supertranslations.

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arXiv2020

Exploring Exceptional Drinfeld Geometries

We explore geometries that give rise to a novel algebraic structure, the Exceptional Drinfeld Algebra, which has recently been proposed as an approach to study generalised U-dualities, similar to the non-Abelian and Poisson-Lie generalisations of T-duality. This algebra is generically not a Lie algebra but a Leibniz algebra, and can be realised in exceptional generalised geometry or exceptional field theory through a set of frame fields giving a generalised parallelisation. We provide examples including "three-algebra geometries", which encode the structure constants for three-algebras and in some cases give novel uplifts for $CSO(p,q,r)$ gaugings of seven-dimensional maximal supergravity. We also discuss the M-theoretic embedding of both non-Abelian and Poisson-Lie T-duality.

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arXiv2019

A worldsheet supersymmetric Newton-Cartan string

We construct a (locally) supersymmetric worldsheet action for a string in a non-relativistic Newton-Cartan background. We do this using a doubled string action, which describes the target space geometry in an $O(D,D)$ covariant manner using a doubled metric and doubled vielbeins. By adopting different parametrisations of these doubled background fields, we can describe both relativistic and non-relativistic geometries. We focus on the torsional Newton-Cartan geometry which can be obtained by null duality/reduction (such null duality is particularly simple for us to implement). The doubled action we use gives the Hamiltonian form of the supersymmetric Newton-Cartan string action automatically, from which we then obtain the equivalent Lagrangian. We extract geometric quantities of interest from the worldsheet couplings and write down the supersymmetry transformations. Our general results should apply to other non-relativistic backgrounds. We comment on the usefulness of the doubled approach as a tool for studying non-relativistic string theory.

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