arXiv subjects

Yasha Neiman

Publications and source records attributed to Yasha Neiman.

At least 19 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.

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arXiv2026

Universal structure in the interactions of massless fields on the lightcone

We consider cubic interactions of massless fields of arbitrary spin in 4 spacetime dimensions, within the lightcone formalism. We extend two key results from flat to (Anti-)de Sitter spacetime. First, we present a simple explicit expression for all the cubic vertices. Second, we prove that the various self-dual/chiral theories, such as Self-Dual Yang-Mills, Self-Dual General Relativity and Chiral Higher-Spin Gravity, are fully consistent with no need for vertices beyond cubic. The key observation behind our results is that all cubic vertices in the lightcone formalism can be expressed as a direct generalization of the "abelian" vertices formed by multiplying linearized curvatures. The simple relationship between flat and (Anti-)de Sitter then follows essentially from the conformal invariance of such linearized curvatures. The price for such simplicity is that our vertex expressions are non-local. It is however easy to bring them into a local form, which we also present.

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.

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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

Unified Lagrangians for gravity and gauge theory

We present a new Lagrangian formulation of General Relativity with cosmological constant, coupled to Yang-Mills gauge theory. The formulation has a manifest color/kinematics-dual structure, both in the choice of fundamental fields and in the way they appear in the Lagrangian. The color/kinematics duality is between gauge and Lorentz generators. The fundamental fields consists of 1-form connections and 0-form curvatures -- a structure inspired by higher-spin gravity. The new formulation can be arrived at by combining appropriate versions of the Plebanski and Chalmers-Siegel Lagrangians, and integrating out the Plebanski 2-form. The construction comes in chiral and non-chiral versions. The chiral version is slightly simpler, and highlights the self-dual sector. The non-chiral one makes parity manifest, and doesn't force us to complexify the theory.

gr-qc↗

arXiv2024

Higher-spin self-dual General Relativity: 6d and 4d pictures, covariant vs. lightcone

We study the higher-spin extension of self-dual General Relativity (GR) with cosmological constant, proposed by Krasnov, Skvortsov and Tran. We show that this theory is actually a gauge-fixing of a 6d diffeomorphism-invariant Abelian theory, living on (4d spacetime)x(2d spinor space) modulo a finite group. On the other hand, we point out that the theory respects the 4d geometry of a self-dual GR solution, with no backreaction from the higher-spin fields. We also present a lightcone ansatz that reduces the covariant fields to one scalar field for each helicity. The field equations governing these scalars have only cubic vertices. We compare our lightcone ansatz to Metsaev's lightcone formalism. We conclude with a new perspective on the lightcone formalism in (A)dS spacetime: not merely a complication of its Minkowski-space cousin, it has a built-in Lorentz covariance, and is closely related to Vasiliev's concept of unfolding.

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arXiv2024

Topology Change from Pointlike Sources

In this paper we study topology-changing spacetimes occurring from pointlike sources. Following an old idea of Penrose, we will opt for a non-Hausdorff model of topology change in which an initial pointlike source is ``doubled" and allowed to propagate along null rays into an eventual cobordism. By appealing to recent developments in non-Hausdorff differential geometry, we will describe and evaluate gravitational actions on these topology-changing spacetimes. Motivated by analogous results for the Trousers space, we describe a sign convention for Lorentzian angles that will ensure the dampening of our non-Hausdorff topology-changing spacetimes within a two-dimensional path integral for gravity.

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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arXiv2023

Self-dual gravity in de Sitter space: lightcone ansatz and static-patch scattering

Using Krasnov's formulation of General Relativity (GR), we develop a lightcone ansatz for self-dual gravity (along with linearized anti-self-dual perturbations) in the Poincare patch of de Sitter space. This amounts to a generalization of Plebanski's "second heavenly equation" to non-zero cosmological constant. The only interaction vertices are cubic ones, found previously by Metsaev in a bottom-up lightcone approach. We point out a special feature of these vertices, which leads to "almost conservation" of energy at each successive order in perturbation theory, despite the time-dependent de Sitter background. Since we embed the lightcone variables into a full spacetime metric, the solutions have a clear geometric interpretation. In particular, this allows us to read off boundary data on both the past and future horizons of a causal (static) patch. In this way, we add self-dual GR to the program of defining & computing scattering amplitudes in a causal patch of de Sitter space.

gr-qc↗

arXiv2023

Quartic locality of higher-spin gravity in de Sitter and Euclidean anti-de Sitter space

We consider higher-spin gravity in (A)dS_4, defined as the holographic dual of a free O(N) or Sp(N) vector model. At the quartic level, this theory has been judged non-local at distances greater than the (A)dS radius, due to a mismatch of massless (twist=1) exchange-type terms in its boundary OPE behavior. We review the non-locality argument, and note that it relies on a double-lightcone limit, which requires a Lorentzian boundary. In the Euclidean OPE limit, we demonstrate the absence of massless exchange-type non-localities of any spin, by inspecting a known formula for the bulk exchange diagrams in Euclidean AdS, and constructing upper bounds in which the spin-dependence factorizes from the position-dependence. Our results suggest that higher-spin theory is local (at distances greater than the curvature radius) in spacetimes with Euclidean boundary signature. For Lorentzian bulk, this implies locality in de Sitter space, as opposed to anti-de Sitter.

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arXiv2022

New diagrammatic framework for higher-spin gravity

We consider minimal type-A higher-spin (HS) gravity in four dimensions, at tree level. We propose new diagrammatic rules for this theory, involving both Fronsdal fields and Didenko-Vasiliev (DV) particles - linearized versions of HS gravity's "BPS black hole". The vertices include a standard minimal coupling between particle and gauge field, the Sleight-Taronna cubic vertex for HS fields, and a recently introduced vertex coupling two HS fields to a DV particle. We show how these ingredients can be combined to reproduce all n-point functions of the theory's holographic dual - the free O(N) vector model. Our diagrammatic rules interpolate between the usual ones of field theory and those of string theory. Our construction can be viewed as a bulk realization of HS algebra.

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arXiv2022

Bulk locality and gauge invariance for boundary-bilocal cubic correlators in higher-spin gravity

We consider type-A higher-spin gravity in 4 dimensions, holographically dual to a free O(N) vector model. In this theory, the cubic correlators of higher-spin boundary currents are reproduced in the bulk by the Sleight-Taronna cubic vertex. We extend these cubic correlators from local boundary currents to bilocal boundary operators, which contain the tower of local currents in their Taylor expansion. In the bulk, these boundary bilocals are represented by linearized Didenko-Vasiliev (DV) "black holes". We argue that the cubic correlators are still described by local bulk structures, which include a new vertex coupling two higher-spin fields to the "worldline" of a DV solution. As an illustration of the general argument, we analyze numerically the correlator of two local scalars and one bilocal. We also prove a gauge-invariance property of the Sleight-Taronna vertex outside its original range of applicability: in the absence of sources, it is invariant not just within tranverse-traceless gauge, but rather in general traceless gauge, which in particular includes the DV solution away from its "worldline".

hep-th↗

arXiv2022

Higher-spin gravity's "string": new gauge and proof of holographic duality for the linearized Didenko-Vasiliev solution

We consider type-A higher-spin gravity in AdS_4, holographically dual to a free U(N) vector model on the boundary. We study the linearized version of the Didenko-Vasiliev "BPS black hole", which we view as this theory's equivalent of the fundamental string. The Didenko-Vasiliev solution consists of gauge fields of all spins generated by a particle-like source along a bulk geodesic, and is holographically dual to a bilocal boundary operator at the geodesic's endpoints. Our first main result is a new gauge for this solution, which makes manifest its behavior under the boundary field equation. It can be viewed as an AdS uplift of flat spacetime's de Donder gauge, but is not de Donder in AdS. To our knowledge, this gauge is novel even in the spin-2 sector, and thus provides a new expression for the linearized gravitational field of a massive point particle in (A)dS_4. Our second main result is a proof of the holographic duality between the mutual bulk action of two Didenko-Vasiliev solutions and the CFT correlator of two boundary bilocals. As an intermediate step, we show that in a bilocal->local limit, the Didenko-Vasiliev solution reproduces the standard boundary-bulk propagators of all spins. We work in the "metric-like" language of Fronsdal fields, and use the embedding-space formalism.

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arXiv2021

A microscopic derivation of the quantum measurement postulates

In the mid-19th century, both the laws of mechanics and thermodynamics were known, and both appeared fundamental. This was changed by Boltzmann and Gibbs, who showed that thermodynamics can be *derived*, by applying mechanics to very large systems, and making simple statistical assumptions about their behavior. Similarly, when Quantum Mechanics (QM) was first discovered, it appeared to require two sets of postulates: one about the deterministic evolution of wavefunctions, and another about the probabilistic measurement process. Here again, the latter is derivable from the former: by applying unitary evolution to large systems (apparatuses, observers and environment), and making simple assumptions about their behavior, one can derive all the features of quantum measurement. We set out to demonstrate this claim, using a simple and explicit model of a quantum experiment, which we hope will be clear and compelling to the average physicist.

quant-ph↗

arXiv2021

MHV amplitudes and BCFW recursion for Yang-Mills theory in the de Sitter static patch

We study the scattering problem in the static patch of de Sitter space, i.e. the problem of field evolution between the past and future horizons of a de Sitter observer. We formulate the problem in terms of off-shell fields in Poincare coordinates. This is especially convenient for conformal theories, where the static patch can be viewed as a flat causal diamond, with one tip at the origin and the other at timelike infinity. As an important example, we consider Yang-Mills theory at tree level. We find that static-patch scattering for Yang-Mills is subject to BCFW-like recursion relations. These can reduce any static-patch amplitude to one with N^{-1}MHV helicity structure, dressed by ordinary Minkowski amplitudes. We derive all the N^{-1}MHV static-patch amplitudes from self-dual Yang-Mills field solutions. Using the recursion relations, we then derive from these an infinite set of MHV amplitudes, with arbitrary number of external legs.

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arXiv2020

Scattering in the static patch of de Sitter space

We study the scattering problem in the static patch of de Sitter space, i.e. the problem of field evolution between the past and future horizons of a de Sitter observer. We calculate the leading-order scattering for a conformally massless scalar with cubic interaction, as both the simplest case and a warmup towards Yang-Mills and gravity. Our strategy is to decompose the static-patch evolution problem into a pair of more symmetric evolution problems in two Poincare patches, sewn together by a spatial inversion. To carry this out explicitly, we end up developing formulas for the momentum-space effect of inversions in flat spacetime. The geometric construction of an electron's 4-momentum and spin vectors from a Dirac spinor turns out to be surprisingly relevant.

hep-th↗

arXiv2020

Higher-spin symmetry vs. boundary locality, and a rehabilitation of dS/CFT

We consider the holographic duality between 4d type-A higher-spin gravity and a 3d free vector model. It is known that the Feynman diagrams for boundary correlators can be encapsulated in an HS-algebraic twistorial expression. This expression can be evaluated not just on separate boundary insertions, but on entire finite source distributions. We do so for the first time, and find that the result Z_HS disagrees with the usual CFT partition function. While such disagreement was expected due to contact corrections, it persists even in their absence. We ascribe it to a confusion between on-shell and off-shell boundary calculations. In Lorentzian boundary signature, this manifests via wrong relative signs for Feynman diagrams with different permutations of the source points. In Euclidean, the signs are instead ambiguous, spoiling would-be linear superpositions. Framing the situation as a conflict between boundary locality and HS symmetry, we sacrifice locality and choose to take Z_HS seriously. We are rewarded by the dissolution of a long-standing pathology in higher-spin dS/CFT. Though we lose the connection to the local CFT, the precise form of Z_HS can be recovered from first principles, by demanding a spin-local boundary action.

hep-th↗

arXiv2020

Bulk interactions and boundary dual of higher-spin-charged particles

We consider higher-spin gravity in (Euclidean) AdS_4, dual to a free vector model on the 3d boundary. In the bulk theory, we study the linearized version of the Didenko-Vasiliev black hole solution: a particle that couples to the gauge fields of all spins through a BPS-like pattern of charges. We study the interaction between two such particles at leading order. The sum over spins cancels the UV divergences that occur when the two particles are brought close together, for (almost) any value of the relative velocity. This is a higher-spin enhancement of supergravity's famous feature, the cancellation of the electric and gravitational forces between two BPS particles at rest. In the holographic context, we point out that these "Didenko-Vasiliev particles" are just the bulk duals of bilocal operators in the boundary theory. For this identification, we use the Penrose transform between bulk fields and twistor functions, together with its holographic dual that relates twistor functions to boundary sources. In the resulting picture, the interaction between two Didenko-Vasiliev particles is just a geodesic Witten diagram that calculates the correlator of two boundary bilocals. We speculate on implications for a possible reformulation of the bulk theory, and for its non-locality issues.

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