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Jiajie Mei

Publications and source records attributed to Jiajie Mei.

At least 19 recordsLinked to original sources
arXiv2026

A compact analytic formula for the one-loop triangle cosmological correlator

We derive a compact analytic formula for the one-loop triangle correlator of conformally coupled scalars in de Sitter space. The result is organised as six leading-singularity prefactors multiplying pure weight-two functions of the six energy variables. It contains forty-two dilogarithms, compared with approximately one hundred and twenty in the previously known closed-form representation, and requires no auxiliary regulator. The dilogarithms occur in Galois-conjugate pairs, making each contribution separately real throughout the physical region. We validate the result numerically. Moreover, we show that its symbol can be derived directly from the dressed integral representation or, independently, bootstrapped from Landau singularities and general consistency conditions. Finally, we show that the correlator (in a suitable normalization) is a Stieltjes function of each squared energy separately and is jointly completely monotone in all six squared energies. These structures suggest a route towards higher-point one-loop cosmological correlators.

hep-th↗
arXiv2026

From Cosmological Cuts to Yang--Mills Wavefunctions in de Sitter Space

We study tree-level Yang--Mills wavefunctions in four-dimensional de Sitter space using their discontinuities. Cosmological cuts factorize gluon discontinuities into lower-point wavefunctions glued by cut propagators and transverse projectors. For ray-like trees and one-loop $n$-gons, the maximal cuts take a particularly simple form: a scalar $ϕ^3$ discontinuity dressed by an ordered Yang--Mills numerator built from local gluing maps. We then use these cuts as reconstruction data for the four-, five-, and six-gluon wavefunctions in momentum space. The result separates into a cut-detectable part obtained from lower-point gluing and a cut-invisible completion fixed by current conservation and the flat-space limit. Through six points, the terms without longitudinal propagators follow the pole structure of color-ordered scalar $ϕ^3+ϕ^4$ wavefunctions, dressed by local Yang--Mills numerators. Longitudinal propagators collapse part of this scalar structure into contact-type contributions, with the first internal-line corrections appearing at six points. The reconstructed expressions agree with direct momentum-space Feynman-rule computations and give concrete low-point data for an all-$n$ organization of spinning de Sitter wavefunctions.

hep-th↗
arXiv2026

Beyond Discontinuities: Cosmological WFCs and the Supersymmetric Orthogonal Grassmannian

We construct an $\mathcal N=2$ supersymmetric Grassmannian representation of tree-level wavefunction coefficients (WFCs) by combining Grassmannian representations of energy discontinuities with an inversion formula. Since the orthogonal Grassmannian captures homogeneous solutions of the spinor conformal Ward identities, while current WFCs satisfy inhomogeneous Ward identities, the full WFC is obtained by reconstructing the energy-dependent prefactors from a basis of discontinuities. We first demonstrate this mechanism at three points, where the triple discontinuity determines the transverse current WFC and admits a supersymmetric uplift. At four points, we invert a spanning set of five current discontinuities and embed the result in momentum superspace using super-orthogonal-Grassmannian invariants generated by $\hatδ(CΩΞ^I)$. This yields the full four-point super WFC in Grassmannian form. We show that the two orthogonal-Grassmannian branches organize distinct supersymmetric invariants and reduce, in the flat-space limit, to different helicity superamplitudes.

hep-th↗
arXiv2026

Cosmological Dressing Rules

The basic observables in cosmology are known as in-in correlators. Recent calculations have revealed that in-in correlators in four dimensional de Sitter space exhibit hidden simplicity stemming from a close relation to scattering amplitudes in flat space. In this paper we explain how to make this property manifest by dressing flat space Feynman diagrams with certain auxiliary propagators. These dressing rules are derived for conformally coupled and massless scalar theories and we show that they reproduce the same infrared divergences predicted by the Schwinger-Keldysh formalism.

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arXiv2026

Cosmological Correlator Discontinuities from Scattering Amplitudes

Recent theoretical work has revealed that basic observables of quantum field theory in de Sitter space, known as in-in or cosmological correlators, exhibit surprisingly simple mathematical structure reminiscent of scattering amplitudes in flat space. For many theories, this simplicity can be made manifest using a set of ``cosmological dressing rules'' which uplift flat-space Feynman diagrams to in-in correlators in de Sitter space by attaching auxiliary propagators to the interaction vertices. In this paper, we show that discontinuities of cosmological correlators with respect to internal energy variables can be obtained by applying auxiliary propagators to unitarity cuts of flat space Feynman diagrams. Moreover, discontinuities with respect to external energy variables can be obtained by cutting auxiliary propagators attached to Feynman diagrams. This observation in turn implies highly non-trivial constraints on cosmological correlators in the form of simple sum rules. We illustrate these ideas in a number of examples at tree-level and 1-loop for conformally coupled scalar theories, although they hold more generally. Finally, we show how to reconstruct cosmological correlators from their discontinuities using dispersion relations, providing a powerful new approach to computing cosmological observables by systematically reconstructing them from data uplifted from flat space.

hep-th↗
arXiv2025

Constraints on Long-Range Forces in De Sitter Space

The representation theory of de Sitter space admits partially massless (PM) particles, but whether such particles can participate in consistent interacting theories remains unclear. We investigate the consistency of theories containing PM fields, particularly when these fields are coupled to gravity. Our strategy exploits the fact that PM fields correspond to partially conserved currents on the spacetime boundary, which generate symmetries. These symmetries place stringent constraints on correlation functions of charged operators, allowing us to test the consistency of a proposed bulk spectrum. When the assumed operator content violates these constraints, the corresponding bulk theory is ruled out. Applying this framework, we show that, in four-dimensional de Sitter space, PM fields of spin 2 or 3 (at depth 0) cannot couple consistently to gravity: such couplings necessitate additional massive fields, which are inevitably non-unitary. In higher dimensions, however, the constraints can be satisfied without violating unitarity if further PM fields are included. The resulting structure leads to additional charge conservation laws, which suggests that consistency may ultimately require an infinite tower of higher-spin PM fields, akin to the situation for ordinary higher-spin symmetries. The methods developed here provide powerful constraints on possible long-range interactions in de Sitter space and delineate the landscape of consistent quantum field theories in cosmological spacetimes.

hep-th↗
arXiv2024

Soft Limits of Gluon and Graviton Correlators in Anti-de Sitter Space

We derive formulae for the soft limit of tree-level gluon and graviton correlators in Anti-de Sitter space, which arise from Feynman diagrams encoding the Weinberg soft theorems in flat space. Other types of diagrams can also contribute to the soft limit at leading order in the soft momentum, but have a different pole structure. We derive these results at four points using explicit formulae recently obtained from the cosmological bootstrap and double copy, and extend them to any multiplicity using bootstrap techniques in Mellin-momentum space.

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arXiv2024

From on-shell amplitude in AdS to cosmological correlators: gluons and gravitons

We recently introduced a recursive bootstrap method for constructing $n$-point gluon and graviton Mellin-momentum amplitudes in (A)dS spacetime. The power of this approach was illustrated by our successful computation of the first five-point graviton amplitude in (A)dS. In this work, we provide further details of these calculations and start with a more in-depth review of the formalism by offering detailed insights into the motivation for defining on-shell amplitudes in AdS, along with various explicit examples. Furthermore, we demonstrate how cosmological correlators can be effortlessly obtained once the amplitude is determined.

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arXiv2024

Amplitude Bootstrap in (Anti) de Sitter Space And The Four-Point Graviton from Double Copy

We propose studying a new representation of on-shell Anti de Sitter (AdS) amplitude in Mellin Momentum space, where it encodes all the dynamical information in Cosmological Correlators. At tree level, we demonstrate that this amplitude has a similar analytic structure as the S-matrix, with residues of poles made up of on-shell lower-point amplitudes. We use this structure to bootstrap 4-point scalar amplitudes with spin-1 and spin-2 exchange. In the second part of the paper, we use double copy to construct the 4-point graviton amplitude in general dimension. This leads us to a novel, concise formula that exhibits the flat space structure. We also verified this formula for the case when d=3 with literature.

hep-th↗
arXiv2024

On-shell Bootstrap for n-gluons and gravitons scattering in (A)dS, Unitarity and Soft limit

We propose an algorithm to recursively bootstrap $n$-point gluon and graviton Mellin-Momentum amplitudes in (A)dS spacetime using only three-point amplitude. We discover that gluon amplitudes are simply determined by factorization for $n\geq 5$. The same principle applies to $n$-point graviton amplitudes, but additional constraints such as flat space and soft limits are needed to fix contact terms. Furthermore, we establish a mapping from $n$-point Mellin-Momentum amplitudes to $n$-point cosmological correlators. We efficiently compute explicit examples up to five points. This leads to the first five-graviton amplitude in $AdS_{d+1}$.

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arXiv2024

The Subtle Simplicity of Cosmological Correlators

We investigate cosmological correlators for conformally coupled $ϕ^4$ theory in four-dimensional de Sitter space. These \textit{in-in} correlators differ from scattering amplitudes for massless particles in flat space due to the spacelike structure of future infinity in de Sitter. They also require a regularization which preserves de Sitter-invariance, which makes the flat space limit subtle to define at loop-level. Nevertheless we find that up to two loops, the \textit{in-in} correlators are structurally simpler than the wave function and have the same transcendentality as flat space amplitudes. Moreover, we show that their loop integrands can be recast in terms of flat space integrands and can be derived from a novel recursion relation.

hep-th↗
arXiv2023

Graviton Trispectrum from Gluons

The tree-level wavefunction coefficient for four gravitons in de Sitter space was recently bootstrapped using the Cosmological Optical Theorem, flat space limit, and Manifestly Local Test \cite{Bonifacio:2022vwa}. Inspired by the double copy for scattering amplitudes, we derive a compact new expression for this quantity starting from the wavefunction coefficient for gluons.

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arXiv2023

Bootstrapping Witten diagrams via differential representation in Mellin space

We explore the use of the differential representation of AdS amplitudes to compute Witten diagrams. The differential representation expresses AdS amplitudes in terms of conformal generators acting on contact Witten diagrams, which allows us to construct differential equations for Witten diagrams. These differential equations can then be transformed into difference equations in Mellin space, which can be solved recursively. Using this method, we efficiently re-computed scalar four-point amplitudes and obtained new results for scalar six-point amplitudes mediated by gluons and scalars, as well as two examples of scalar eight-point amplitudes from gluon exchange.

hep-th↗
arXiv2022

New recursions for tree-level correlators in (Anti) de Sitter space

We present for the first time classical multiparticle solutions in Anti de Sitter space (AdS) involving scalars, gluons, and gravitons. They are recursively defined through multiparticle currents which reduce to Berends-Giele currents in the flat space limit. This construction exposes a compact definition of tree-level boundary correlators using a general prescription that removes unphysical boundary contributions. Similarly to the flat space perturbiner, a convenient gauge choice leads to a scalar basis for all degrees of freedom, while the tensor structure is exclusively captured by field theory vertices. This provides a fully automated way to compute AdS boundary correlators to any multiplicity and cosmological wavefunction coefficients after Wick-rotating to de Sitter space.

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arXiv2022

Enhanced Soft Limits in de Sitter Space

In flat space, the scattering amplitudes of certain scalar effective field theories exhibit enhanced soft limits due to the presence of hidden symmetries. In this paper, we show that this phenomenon extends to wavefunction coefficients in de Sitter space. Using a representation in terms of boundary conformal generators acting on contact diagrams, we find that imposing enhanced soft limits fixes the masses and four-point couplings (including curvature corrections) in agreement with Lagrangians recently derived from hidden symmetries. Higher-point couplings can then be fixed using a bootstrap procedure which we illustrate at six points. We also discuss implications for the double copy in de Sitter space.

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arXiv2022

Effective Field Theories and Cosmological Scattering Equations

We propose worldsheet formulae for wavefunction coefficients of the massive non-linear sigma model (NLSM), scalar Dirac-Born-Infeld (DBI), and special Galileon (sGal) theories in de Sitter momentum space in terms of the recently proposed cosmological scattering equations constructed from conformal generators in the future boundary. The four-point integrands are assembled from simple building blocks and we identify a double copy prescription mapping the NLSM wavefunction coefficient to the DBI and sGal wavefunction coefficients, including mass deformations and curvature corrections. Finally, we compute the soft limits of these wavefunction coefficients and find that they can be written in terms of boundary conformal generators acting on contact diagrams.

hep-th↗
arXiv2021

Weakly Supervised Video Anomaly Detection via Center-guided Discriminative Learning

Anomaly detection in surveillance videos is a challenging task due to the diversity of anomalous video content and duration. In this paper, we consider video anomaly detection as a regression problem with respect to anomaly scores of video clips under weak supervision. Hence, we propose an anomaly detection framework, called Anomaly Regression Net (AR-Net), which only requires video-level labels in training stage. Further, to learn discriminative features for anomaly detection, we design a dynamic multiple-instance learning loss and a center loss for the proposed AR-Net. The former is used to enlarge the inter-class distance between anomalous and normal instances, while the latter is proposed to reduce the intra-class distance of normal instances. Comprehensive experiments are performed on a challenging benchmark: ShanghaiTech. Our method yields a new state-of-the-art result for video anomaly detection on ShanghaiTech dataset

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