arXiv subjects

Nicolas Boulanger

Publications and source records attributed to Nicolas Boulanger.

At least 19 recordsLinked to original sources

arXiv2026

Conformal Renormalisation of 8D Einstein Gravity

We show that Holographic Renormalisation (HR) in eight dimensions is encoded in the unique conformal gravity theory that admits an Einstein sector with constant negative curvature. We explicitly relate HR to Topological Regularisation (TR), where the latter prescribes to add the Euler term to the Einstein-Hilbert Lagrangian density, with a precise coefficient so as to ensure that the resulting density is polynomial in the anti de Sitter (AdS) curvature. The polynomial is still asymptotically divergent. We find that the aforementioned, unique conformal gravity action in 8D, reproduces the polynomial, together with extra boundary terms that cancel the divergent terms in the action. We conjecture that, in arbitrary even dimension, HR is equivalent to conformally completing the Einstein-Hilbert action with negative cosmological constant, plus the Euler term with fixed coupling prescribed by TR.

hep-th↗

arXiv2026

Higher-spin self-dual gravity from holomorphic planes in twistor space

We prove a `nonlinear graviton theorem' for higher-spin self-dual gravity. We consider small deformations of the complex structure of the non-projective twistor space that are bounded in a specified region near the origin and investigate the space $M_{HS}$ of holomorphically embedded complex planes $\mathbb{C}^2$ that intersect the origin. We show that this space is an infinite dimensional complex manifold with a canonical projection onto a four-dimensional holomorphic self-dual spacetime $\mathcal{M}$, and discuss the geometry induced on this new higher-spin space. Solutions of higher-spin self-dual gravity are then obtained by choosing an embedding of spacetime $\mathcal{M}$ into higher-spin space $M_{HS}$, with higher-spin symmetries arising from the different choices of embedding. Integrability of the theory is manifested in the form of a Lax pair for the system that we present. We conjecture that chiral higher-spin gravity can similarly be realized by considering deformations that are unconstrained at the origin.

hep-th↗

arXiv2026

Higher dualities in $E_{11}$ exceptional field theory

It was proposed that there exists an $E_{11}$-invariant formulation of eleven-dimensional supergravity in which the propagating fields of the theory are realised through an infinite tower of higher duals. We show how to derive the propagating equations of the higher dual fields within $E_{11}$ exceptional field theory at the linearised level. Starting from the pseudo-Lagrangian, we construct parent actions for all higher gradient dual fields that are associated with the three-form, the six-form, and the dual graviton. We show that the resulting Euler-Lagrange equations constrain the St\"uckelberg fields to be pure curls, ensuring that the higher duals propagate the same physical degrees of freedom as the original supergravity fields. The additional St\"uckelberg fields, which are not predicted by the tensor hierarchy algebra, are shown to play a specific role as sources for the Labastida tensors of the higher dual fields.

hep-th↗

arXiv2026

The complete action for $\mathcal{N}=2$ de Sitter pure supergravity

Supergravity theories in de Sitter spacetime are known to be very constrained, and rather unnatural within String/M Theory. We revisit the seminal paper by Pilch, van Nieuwenhuizen and Sohnius, where the possible existence of a real Lagrangian for ${\cal N}=2$ pure supergravity in four-dimensional de Sitter spacetime was pointed out. We clarify several issues related to the non-unitarity of the theory and explicitly construct the unique, complete theory searched for long ago by the aforementioned authors. We argue that the lack of unitarity of the Lorentzian theory may be revisited in the Euclidean approach to de Sitter quantum gravity, where alternative definitions of unitarity can be introduced.

hep-th↗

arXiv2026

Kinematical Lie algebras and symplectic symmetric spaces I: Lie algebraic aspects

We generalize the notion of kinematical Lie algebra introduced in physics for the classification of the various possible relativity algebras an isotropic spacetime can accommodate. We first give an elementary proof of the fact that such a generalized kinematical Lie algebra $\mathfrak{g}$ always carries a canonical structure of symplectic involutive Lie algebra (shortly ``siLa''). In other words, if $G$ is a connected Lie group admitting $\mathfrak{g}$ as Lie algebra, there always exists a Lie subgroup $H$ of $G$ constituted by the elements of $G$ that are fixed under an involutive automorphism of $G$ and such that the homogenenous space $M=G/H$ is a symplectic symmetric space. In particular, the manifold $M$ canonically carries a $G$-invariant linear torsionfree connection $\nabla$ whose geodesic symmetries centered at all points extend as global $\nabla$-affine transformations of $M$. The manifold $M$ is also canonically equipped with a symplectic structure $ω$ which is invariant under every geodesic symmetry, implying in particular that it is parallel w.r.t the linear connection: $\nablaω=0$. In a second part, we give a complete description of the fine structure of our generalized siLa's. Our discussion yields a complete classification of such sila's.

math.DG↗

arXiv2025

8D conformal gravity with Einstein sector, and its relation to the Q-curvature

We first streamline the construction of the unique six-dimensional conformal gravity action found by Lü, Pang and Pope, that admits Einstein metrics as solutions to the field equations. We then prove that there exists a unique eight-dimensional conformal gravity action that admits Einstein metrics as solutions to the field equations, and explicitly build the corresponding action. Finally, we relate these results to Branson's Q-curvature and the Fefferman-Graham obstruction tensor, to conclude that on every even-dimensional space there exists a unique -- up to boundary terms -- conformally-invariant gravity theory that is extremised by Einstein metrics.

hep-th↗

arXiv2025

Reframing classical mechanics: An AKSZ sigma model perspective

The path-integral re-formulation due to E. Gozzi, M. Regini, M. Reuter and W. D. Thacker of Koopman and von Neumann's original operator formulation of a classical Hamiltonian system on a symplectic manifold $M$ is identified as a gauge slice of a one-dimensional Alexandrov--Kontsevich--Schwarz--Zaboronsky sigma model with target $T^\ast(T[1]M\times \mathbb{R}[1])$.

hep-th↗

arXiv2025

Unfolding $E_{11}$

We work out the unfolded formulation of the fields in the non-linear realisation of $E_{11}$. Using the connections in this formalism, we propose, at the linearised level, an infinite number of first-order duality relations between the dual fields in $E_{11}$. In this way, we introduce extra fields that do not belong to $E_{11}$ and we investigate their origin. The equations of motion of the fields are obtained by taking derivatives and higher traces of the duality relations.

hep-th↗

arXiv2025

A note on partially massless supergravity

We analyse the couplings of a partially massless spin-2 field with a doublet of massless, real spin-3/2 fields. In the flat limit, this spectrum coincides with the spectrum of ${\cal N}=2$ pure supergravity around anti-de Sitter spacetime AdS$_4$. We classify all the possible parity-invariant, non-Abelian deformations of the free theory that lead to a deformation of the Lagrangian. By doing this, we re-derive a non-Abelian vertex recently found in 2412.04982 [hep-th] by Yu. M. Zinoviev following a different approach, and show that the corresponding non-Abelian gauge algebra closely resembles the one of ${\cal N}=2$ supergravity around AdS$_4$. The gauge-algebra deformation is however obstructed, at next order. Then, we add a massless vector field together with a massive spin-3/2 field, and find two nontrivial vertices mixing these fields with a single massless gravitino. Still, the gauge algebra remains obstructed at next order, therefore excluding the possibility to make local the global supersymmetry algebra found in recent works on partially massless supermultiplets in AdS$_4$. Finally, we argue that the two problems encountered are simultaneously solved by the addition of the masseless graviton, leading to ${\cal N}=1$ pure conformal supergravity around AdS$_4$ as the only consistent theory coupling partially massless spin-2 fields to massless and massive spin-3/2 fields.

hep-th↗

arXiv2024

Cubic interactions for massless and partially massless spin-1 and spin-2 fields

We perform a complete classification of the consistent two-derivative cubic couplings for a system containing an arbitrary number of massless spin-1, massless spin-2, and partially massless (PM) spin-2 fields in $D$-dimensional (anti-)de Sitter space. In addition to previously known results, we find a unique candidate mixing between spin-1 and PM spin-2 fields. We derive all the quadratic constraints on the structure constants of the theory, allowing for relative ``wrong-sign'' kinetic terms for any of the fields. In the particular case when the kinetic terms in each sector have no relative signs, we find that the unique consistent non-trivial theory is given by multiple independent copies of conformal gravity coupled to a Yang-Mills sector in $D=4$. Our results strengthen the well-known no-go theorems on the absence of mutual interactions for massless and PM spin-2 fields.

hep-th↗

arXiv2024

Structural and optical characterization of NiO polycrystalline thin films fabricated by spray-pyrolysis

Nickel (II) oxide, NiO, a wide band gap Mott insulator characterized by strong Coulomb repulsion between d-electrons and displaying antiferromagnetic order at room temperature, has gained attention in recent years as a very promising candidate for applications in a broad set of areas, including chemistry and metallurgy to spintronics and energy harvesting. Here, we report on the synthesis of polycrystalline NiO fabricated using spray-pyrolysis technique, which is a deposition technique able to produce quite uniform films of pure and crystalline materials without the need of high vacuum or inert atmospheres. We then characterized the composition and structure of our NiO thin films using X-ray diffraction, and atomic force and scanning electron microscopies, respectively. We completed our study by looking at the phononic and magnonic properties of our NiO thin films via Raman spectroscopy, and at the ultrafast electron dynamics by using optical pump probe spectroscopy. We found that our NiO samples display the same phononic and magnonic dispersion expected for single crystal NiO at room temperature, and that electron dynamics in our system is similar to those of previously reported NiO mono- and poli-crystalline systems synthesized with different techniques. These results prove that spray-pyrolysis can be used as affordable and large-scale fabrication technique to synthetize strongly correlated materials for a large set of applications.

cond-mat.mtrl-sci↗

arXiv2023

Conformal boundaries of Minkowski superspace and their super cuts

In this article we carry out a detailed investigation of the geometric nature of the points at infinity of Minkowski superspace. It turns out that there are several sets of points forming the superconformal boundary of Minkowski superspace: on top of a well-behaved super $\mathscr{I}$, we find other sets that we exhibit and study. We also study the intersection of these boundaries with super null cones and explicitly construct the corresponding space of super cuts.

hep-th↗

arXiv2023

Strange higher-spin topological systems in 3D

Motivated by the generation of action principles from off-shell dualisation, we present a general class of free, topological theories in three dimensional Minkowski spacetime that exhibit higher-spin gauge invariance. In the spin-two case, we recover a dual reformulation of the triplet system already known, while the higher-spin systems that we obtain seem to be new. They are associated with wild quivers. We study in which situations these exotic (or strange) higher-spin models can be extended to dS${}_3$ and AdS${}_3$ backgrounds, revealing that the flat limit of such models, when they exist, admits a one-parameter freedom. Interactions are studied in the simplest higher-spin case featuring spin-2 and spin-3 fields. We then give several higher-spin generalisations of these strange systems.

hep-th↗

arXiv2023

Consistent couplings between a massive spin-3/2 field and a partially massless spin-2 field

We revisit the problem of constructing consistent interactions between a massive spin-3/2 field and a partially massless graviton in four-dimensional (A)dS spacetime. We use the Stueckelberg formulation of the action principle for these fields and find two non-trivial cubic vertices with less than two derivatives, when going to the unitary gauge. One of the vertices is reminiscent of the minimal coupling of the massive spin-3/2 field to gravity, except that now the graviton is partially massless.

hep-th↗

arXiv2023

Higher dualisations of linearised gravity and the $A_1^{+++}$ algebra

The non-linear realisation based on $A_1^{+++}$ is known to describe gravity in terms of both the graviton and the dual graviton. We extend this analysis at the linearised level to find the equations of motion for the first higher dual description of gravity that it contains. We also give a systematic method for finding the additional fields beyond those in the non-linear realisation that are required to construct actions for all of the possible dual descriptions of gravity in the non-linear realisation. We show that these additional fields are closely correlated with the second fundamental representation of $A_1^{+++}\,$.

hep-th↗

arXiv2023

New higher-spin curvatures in flat space

It was shown that the Lie algebra underlying higher-spin holography admits a contraction including a Poincaré subalgebra in any space-time dimensions. The associated curvatures, however, do not reproduce upon linearisation those that are usually employed to formulate the equations of motion of free massless particles in Minkowski space. We show that, despite this mismatch, the new linearised curvatures can also be used to describe massless higher-spin fields. This suggests a new way to build interacting higher-spin gauge theories in Minkowski space that may admit a holographic description.

hep-th↗

arXiv2023

Ambient-space variational calculus for gauge fields on constant-curvature spacetimes

We propose a systematic generating procedure to construct free Lagrangians for massive, massless and partially massless, totally-symmetric tensor fields on $AdS_{d+1}$ starting from the BRST Lagrangian description of massless fields in the flat ambient space $\mathbb{R}^{d,2}$. A novelty is that the Lagrangian is described by a $d+1$ form on $\mathbb{R}^{d,2}$ whose pullback to $AdS_{d+1}$ gives the genuine Lagrangian defined on anti de Sitter spacetime. Our derivation uses the triplet formulation originating from the first-quantized BRST approach, where the action principle is determined by the BRST operator and the inner product of a first-quantised system. In this way we build, in a manifestly $so(2,d)$-covariant manner, a unifying action principle for the three types of fields mentioned above. In particular, our derivation justifies the form of some actions proposed earlier for massive and massless fields on AdS. We also give a general setup for ambient Lagrangians in terms of the respective jet-bundles and variational bi-complexes. In particular we introduce a suitable ambient-space Euler-Lagrange differential which allows to derive the equation of motion ambiently, i.e. without the need to explicitly derive the respective spacetime Lagrangian.

hep-th↗

arXiv2022

Snowmass White Paper: Higher Spin Gravity and Higher Spin Symmetry

Higher Spin Gravity refers to extensions of gravity including at least one field of spin greater than two. These extensions are expected to provide manageable models of quantum gravity thanks to the infinite-dimensional (higher spin) gauge symmetry constraining them. One of the key aspects of Higher Spin Gravity/Symmetry is the range and diversity of topics it embraces: (a) higher spin fields play a role in quantum gravity, AdS/CFT, string theory and are expected to have important consequences in cosmology and black hole physics; (b) higher spin symmetry finds applications in Conformal Field Theories, condensed matter systems and dualities therein; (c) these models often rely on tools developed in the study of the mathematical foundations of QFT or in pure mathematics: from deformation quantization and non-commutative geometry to conformal geometry, graded geometry (including BV-BRST quantization), and geometry of PDEs. Recent exciting applications also involve (d) modelling the coalescence of black hole binaries as scattering of massive higher spin particles.

hep-th↗