arXiv subjects

Julian Lang

Publications and source records attributed to Julian Lang.

6 recordsLinked to original sources

arXiv2026

Higher-Spin dS/CFT beyond minimal type-A, and the doubled nature of de Sitter space

We study the holographic duality between free vector models and Higher-Spin Gravity in 4-dimensional de Sitter space. On both the bulk and boundary sides, we introduce new reality conditions, which allow us to include odd spins in the bulk, and to extend the duality from type-A to type-B (i.e. from boundary scalars to spinors). The new reality conditions are closely related to a higher-spin-symmetric Hilbert-space norm for the single-particle (super)multiplet in de Sitter space. We construct two alternative viewpoints on the type-A and type-B theories. In one view, the two co-exist in "parallel universes", specifically in even vs. odd antipodal identifications of de Sitter space. In the other view, type-A and type-B are Legendre-transformed descriptions of the same twistor-space theory in Euclidean AdS (this involves the observation that the higher-spin partition function is Legendre-dual to itself). In this way, higher-spin holography reconciles the two-boundary nature of de Sitter space with the one-boundary nature of Euclidean AdS. The supersymmetric theory that unifies type-A and type-B with bulk fermions fails to be consistent under the appropriate reality conditions.

hep-th↗

arXiv2026

BRST methods for constructing quartic actions for spinning black holes

We develop a systematic approach to the computation of gauge invariant quartic interactions between reducible massive and massless higher spin fields. Extending the BRST formulation of existing cubic results, we obtain a single constraint for each off-shell quartic vertex that ensures both the gauge invariance of the Lagrangian and associativity of the gauge transformations at quartic order. A solution to these equations is presented. The general equation is then reduced to an on-shell version to reduce complexity. We find example solutions for the off-shell and on-shell quartic vertices in low spin examples relevant to the problem of black hole scattering.

hep-th↗

arXiv2025

Massive Higher Spins and Black Hole Interactions

We give a brief introduction into the gauge invariant formulation of irreducible massive bosonic higher spin fields. We discuss both free Lagrangians and the ones which include cubic interactions. We demonstrate an application of these Lagrangians to a description of the interactions between Kerr black holes in a Post Minkowskian approximation.

hep-th↗

arXiv2025

Causality of higher-spin interactions on the (A)dS lightcone, with application to the static patch

We study Higher-Spin Gravity in 4-dimensional (Anti-)de Sitter space, at leading order in the interactions (cubic vertices), in the AdS lightcone formalism developed by Metsaev. Using the vertices' chiral structure, we extend the formalism into a broader class of lightcone frames, which allows for lightcones of bulk points. This enables us to write the lightcone theory in de Sitter space, where only these more general frames are available. It also allows us to formulate and verify (for the first time!) some causal properties of massless higher-spin interactions, involving lightcone foliations that share a lightray. These causal properties serve to both motivate and enable the computation of "static-patch scattering amplitudes" - the evolution of fields between the two horizons of the maximal observable region in de Sitter space. We present a computation scheme for such "amplitudes" in coordinate space, and in momentum space with spinor-helicity variables.

hep-th↗

arXiv2025

Theories of the gravity+gauge type in de Sitter space

We study theories of the "General Relativity + Yang-Mills" type in 4d spacetime with cosmological constant, focusing on formulations where the basic variables are connections and curvatures (but no metric). We present a new Lagrangian for GR coupled to Yang-Mills, which uses the same kind of variables for both sectors, and is suggestive of the double-copy structure. This Lagrangian comes in both non-chiral (real) and chiral (complex) versions. The chiral version makes it easy to isolate the self-dual sector. The latter lends itself to a higher-spin (HS) generalization, which combines the HS Self-Dual GR and HS Self-Dual Yang-Mills of Krasnov, Skvortsov and Tran. We then descend from the covariant formulation to lightcone gauge, and construct a cubic-exact lightcone action. For HS Self-Dual Yang-Mills, we solve the lightcone field equations to all orders in perturbation theory. Finally, we discuss the relation between lightcone foliations that share a lightray - a setup relevant for the scattering problem in the de Sitter static patch. We derive this relation at the linearized level, and argue from causality+symmetry that it cannot receive non-linear corrections. We explore the associated gauge transformations in the non-linear covariant theory.

gr-qc↗

arXiv2024

N=2 supersymmetry in the twistor description of higher-spin holography

We study the holographic duality between higher-spin (HS) gravity in 4d and free vector models in 3d, with special attention to the role of N=2 supersymmetry (SUSY). For the type-A bosonic bulk theory, dual to spin-0 fields on the boundary, there exists a twistor-space description; this maps both single-trace boundary operators and linearized bulk fields to spacetime-independent twistor functions, whose HS-algebra products compute all boundary correlators. Here, we extend this description to the type-B bosonic theory (dual to spin-1/2 fields on the boundary), and to the supersymmetric theory containing both. A key role is played by boundary bilocals, which in type-A are dual to the Didenko-Vasiliev 1/2-BPS "black hole". We extend this to an infinite family of linearized 1/2-BPS "black hole" solutions. Remarkably, the full supersymmetric theory (along with the SUSY generators) fits in the same space of twistor functions as the type-A theory. Instead of two sets of bosonic bulk fields, the formalism sees one set of linearized fields, but with both types of boundary data allowed.

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