arXiv subjects

Yunfeng Jiang

Publications and source records attributed to Yunfeng Jiang.

At least 19 recordsLinked to original sources

arXiv2026

A universal scaling function for giant graviton OPE coefficients

We consider the large spin limit $S\to\infty$ of the OPE coefficient for two maximal giant gravitons and a spinning operator with finite twist in planar $\mathcal{N}=4$ super-Yang-Mills theory. Up to an overall normalization factor, this OPE coefficient exhibits a power-law scaling of the form $S^{d(g)}$. We provide strong evidence that the exponent $d(g)$ is free from finite size corrections. Consequently, the all-loop asymptotic expression for the OPE coefficient can be used to determine $d(g)$ exactly. We develop a systematic method to compute the scaling function $d(g)$ for arbitrary values of the 't Hooft coupling $g$. At weak coupling, our result agrees perfectly with the available field-theoretic results up to three-loop order. At strong coupling, we present the first three orders as concrete predictions. We further provide the finite-coupling result and show that it interpolates smoothly between the weak- and strong-coupling regimes.

hep-th↗

arXiv2026

Norms, overlaps and Yangian descendants for the Haldane-Shastry spin chain

The Haldane-Shastry spin chain is a prototypical integrable model with long-range interactions, notable for hosting quasiparticles with fractional statistics and serving as a discrete analogue of a conformal field theory. Its remarkable simplicity is closely tied to a full Yangian spin symmetry. While the highest-weight states for this symmetry are known explicitly, a systematic treatment of the descendant states, needed for the computation of various physical quantities, has remained incomplete. In this work, we provide a detailed construction of these descendants in terms of the algebraic Bethe ansatz following recent work of Ferrando et al. In the limit of extreme twist, it includes the Gelfand-Tsetlin basis. As an application, we derive product and determinant formulae for norms and overlaps of these states.

cond-mat.stat-mech↗

arXiv2026

Quantum Entanglement of Bethe States

We investigate the quantum entanglement of Bethe states across a family of integrable spin chains, including the XXX$_{\frac{1}{2}}$ model, its higher-spin generalizations (XXX$_s$), and the non-compact $SL(2,\mathbb{R})$ chain. For on-shell eigenstates, we perform a comprehensive scan of the bipartite entanglement entropy across the entire spectrum of finite chains with periodic boundary conditions, and identify the Bethe solutions that minimize and maximize the entanglement. These extremal solutions follow systematic, spin-dependent patterns in the Bethe quantum numbers. In the XXX$_{\frac{1}{2}}$ spin chain, for the antiferromagnetic chain, the state with minimal entropy always coincides with the lowest-energy state (the ground state) within a given fixed-magnon sector. For the higher-spin XXX$_s$ model, however, the lowest-entropy state is not always identical to the ground state, and can even be the state of highest energy. By contrast, the Bethe roots that maximize entropy exhibit considerably more intricate structure. Our analysis further reveals how special Bethe root configurations, such as singular and strange solutions, affect entanglement, and it uncovers characteristic entanglement features in the non-compact $SL(2,\mathbb{R})$ chain that are absent from compact spin chains. For off-shell Bethe states, we develop an optimization algorithm that extremizes the entanglement entropy over rapidity distributions, enabling us to explore the maximum entanglement achievable by a Bethe state without imposing the Bethe ansatz equations.

hep-th↗

arXiv2026

Gate Parameter Lee-Yang Zeros and Dynamical Phases in Quantum Circuits

We propose gate-parameter Lee-Yang zeros of Loschmidt amplitudes as probes of dynamical phases in finite quantum circuits. We study Floquet circuits constructed from two-qubit fSim gates with identical parameters, for which the Loschmidt amplitude becomes a rational function of the gate parameters after a suitable change of variables. At fixed system size and large circuit depth, the zeros in one complexified gate parameter, with the other held fixed, condense onto limiting curves. In contrast to conventional Loschmidt or Fisher zeros in complex time, these zeros live directly in the complex plane of a tunable gate parameter. We show that the limiting set has two origins: a state-dependent component controlled by overlaps with Floquet eigenstates, and a universal component fixed by the Floquet spectrum. As the remaining gate parameter is varied, the universal zero set reorganizes abruptly, providing a finite-qubit diagnostic of a dynamical phase transition. We demonstrate this behavior in a Bethe ansatz solvable brickwork circuit and in longer-range fSim circuits outside this solvable structure. The mechanism follows from the Beraha-Kahane-Weiss theorem together with local unitarity, and is therefore spectral rather than a special consequence of integrability.

quant-ph↗

arXiv2026

Fusion of Integrable Defects and the Defect $g$-Function

We study exact defect $g$-functions for integrable line defects in two-dimensional integrable quantum field theory and use them to probe defect fusion. We consider three settings: fusion of purely transmitting topological defects, fusion of non-topological defects with reflection and transmission, and fusion of a defect with an integrable boundary. For topological defects, the separated logarithmic $g$-function is additive, and the fusion limit is controlled by the multiplicative composition of transmission factors. For non-topological defects, separation-dependent phases in the Bethe-Yang equations produce oscillatory finite-size effects, while the fused defect is described by effective reflection and transmission amplitudes. In the Ising examples studied here, fusion involving non-topological defects lowers the finite localized contribution to the entropy, whereas topological defect-boundary fusion leaves it unchanged.

hep-th↗

arXiv2026

Enumerative Geometry on KSBA moduli spaces

We survey two new compactification methods for the KSBA moduli space of general type surfaces so that both of them admit a perfect obstruction theory. Virtual fundamental classes exist on these two moduli spaces, and tautological invariants can be defined on KSBA moduli spaces. This is the starting point to do enumerative geometry on KSBA moduli spaces, and we include some discussions in this direction.

math.AG↗

arXiv2026

Beyond Hagedorn: A Harmonic Approach to $T\bar{T}$-deformation

We apply harmonic analysis to study the $T\bar{T}$-deformed torus partition function. We first express the CFT partition functions in terms of Maass waveforms, including the Eisenstein series and cusp forms. These basis functions turn out to deform in a very simple way under the $T\bar{T}$-deformation. The spectral decomposition provides a numerically stable and efficient method to compute the partition function at finite values of the deformation parameter $λ$, allowing us to clearly resolve the analytic structure of the partition function as a function of $λ$. The resulting deformed partition function exhibits a Hagedorn singularity. Building on harmonic analysis approach, we propose a natural analytic continuation beyond the Hagedorn singularity, which enables us to compute the full partition function for any value of $λ$.

hep-th↗

arXiv2026

The virtual fundamental class for the moduli space of surfaces of general type

We prove that the moduli stack of index-one covers of semi-log-canonical surfaces of general type is isomorphic to the KSBA moduli stack of stable general type surfaces. Using the index-one covering Deligne-Mumford stack of a semi-log-canonical surface, we define the $\lci$ cover. The $\lci$ cover, as a Deligne-Mumford stack, has only locally complete intersection singularities. We then construct the moduli stack of $\lci$ covers so that it admits a proper map to the moduli stack of surfaces of general type. Next, we construct a perfect obstruction theory on this stack and a virtual fundamental class in its Chow group. We then pushforward the virtual fundamental class from the moduli stack of lci covers to the KSBA moduli space. Thus, our construction proves Donaldson's conjecture on the existence of a virtual fundamental class for KSBA moduli spaces. A tautological invariant is defined by integrating a power of the first Chern class of the CM line bundle over the virtual fundamental class. This serves as a generalization of the tautological invariants defined by integrating tautological classes over the moduli space $\overline{M}_g$ of stable curves to the moduli space of stable surfaces.

math.AG↗

arXiv2026

The Roaming Bethe Roots: An Effective Bethe Ansatz Beyond Integrability

We propose an effective Bethe ansatz (EBA) for solving quantum many-body systems near an integrable point. Our approach retains the functional form of the Bethe wave function while renormalizing the Bethe roots to account for integrability-breaking interactions. These effective roots are determined by minimizing physically motivated cost functions. The resulting off-shell Bethe states serve as approximate eigenstates of the non-integrable models. We assess the quality of the approximation using various physical observables, including the energy eigenvalue, state fidelity, and bipartite entanglement entropy. Our tests show that for models with weak integrability-breaking, the effective Bethe ansatz provides a high-quality approximation to the exact eigenstates over a wide range of deformation parameters. In contrast, for models with strong integrability-breaking interactions, the efficacy of the effective Bethe ansatz degrades relatively quickly as the deformation parameter increases. The efficacy of the method thus offers a useful probe for characterizing the strength of integrability breaking. Within its regime of accuracy, it also provides a new representation of the eigenstates of nearly integrable models, enabling one to exploit the algebraic structure inherited from integrability.

cond-mat.stat-mech↗

arXiv2026

Defect Approach to Giant Graviton Dynamics

We develop a framework of zero dimensional defects for analyzing light-light-heavy-heavy (LLHH) correlators in conformal field theories. We specifically apply this formalism to correlators of giant gravitons in $\mathcal{N}=4$ super Yang-Mills to probe the nontrivial physics beyond planarity. By combining this framework with bootstrap techniques, we compute all four-point functions at strong coupling involving two maximal giant gravitons and two supergravitons of arbitrary dimensions. We identify a partially broken, higher-dimensional hidden symmetry -- a defect extension of 10d hidden conformal symmetry -- present at both strong and weak coupling, which allows these correlators to be packaged into a single generating function. Furthermore, we perform a systematic OPE analysis of the strong-coupling correlators, extracting the complete spectrum of anomalous dimensions for the defect-channel double-particle operators. Finally, we argue that the defect perspective provides the natural nonperturbative description for any LLHH correlator by showing that four-point conformal blocks reduce to defect two-point blocks in the heavy limit.

hep-th↗

arXiv2025

Rational $Q$-systems for integrable spin chains without $U(1)$ symmetry

The $Q$-system is an efficient method for finding complete physical solutions of Bethe ansatz equations, but so far its application has been confined to systems possessing $U(1)$ symmetry. We extend the rational $Q$-system framework to integrable spin chains without $U(1)$ symmetry, exemplified by the closed XXZ model with anti-diagonal twists and the open XXZ model with non-diagonal boundary fields. We demonstrate that the $Q$-system can be derived by combining $TQ$-relation with fusion relations of higher-spin transfer matrices. This yields $QQ$-relations analogous to the $U(1)$ symmetric case but incorporating additional inhomogeneous terms. We present numerical solutions that are validated against exact diagonalization, confirming that it generates all and exclusively physical solutions.

hep-th↗

arXiv2025

Equivariant deformation of minimally elliptic singularities

We study certain equivariant deformation components of minimally elliptic surface singularities under finite group actions. Interesting examples include cyclic quotients of simple elliptic singularities and finite group quotients of cusp singularities, where the resulting quotients remain simple elliptic and cusp singularities, respectively. In cases where the minimally elliptic singularities are locally complete intersection (lci) singularities, we identify equivariant deformation components of general type surfaces containing such singularities that admit a perfect obstruction theory.

math.AG↗

arXiv2025

Stochastic Geometry of Cylinders: Characterizing Inter-Nodal Distances for 3D UAV Networks

The analytical characterization of coverage probability in finite three-dimensional wireless networks has long remained an open problem, hindered by the loss of spatial independence in finite-node settings and the coupling between link distances and interference in bounded geometries. This paper closes this gap by presenting the first exact analytical framework for coverage probability in finite 3D networks modeled by a binomial point process within a cylindrical region. To bypass the intractability that has long hindered such analyses, we leverage the independence structure, convolution geometry, and derivative properties of Laplace transforms, yielding a formulation that is both mathematically exact and computationally efficient. Extensive Monte Carlo simulations verify the analysis and demonstrate significant accuracy gains over conventional Poisson-based models. The results generalize to any confined 3D wireless system, including aerial, underwater, and robotic networks.

cs.NI↗

arXiv2025

All Giant Graviton Two-Point Functions at Two-Loops

We present a comprehensive two-loop computation of correlation functions involving two maximal giant gravitons and two arbitrary $R$-charge single-trace half-BPS operators in $\mathcal{N}=4$ Super-Yang-Mills theory. By combining the partially-contracted giant graviton (PCGG) method with the $\mathcal{N}=2$ harmonic superspace formalism, we achieve significant simplifications in perturbative calculations. The resulting correlation functions encode rich CFT data, from which we derive sum rules for the OPE coefficients. These sum rules are in perfect agreement with integrability predictions. Furthermore, at the integrand level, we find a hidden higher dimensional symmetry present at both one- and two-loop orders. This symmetry was discovered recently at strong coupling, which generalizes its counterpart in correlation functions of single-trace operators.

hep-th↗

arXiv2025

Giant Graviton Correlators as Defect Systems

We consider correlation functions of two maximal giant gravitons and two light $\frac{1}{2}$-BPS operators in 4d $\mathcal{N}=4$ SYM. Viewed as two-point correlators in the presence of a zero dimensional defect, they can be completely fixed at strong coupling using analytic bootstrap techniques. We determine all infinitely such correlators for arbitrary light $\frac{1}{2}$-BPS operators and find that the result can be repackaged into a simple generating function thanks to a hidden higher dimensional symmetry. We also find evidence that the same symmetry holds at weak coupling for loop correction integrands.

hep-th↗

arXiv2025

Holographic Wilson Loop One-point Functions in ABJM Theory

We compute the correlation function between a circular half-BPS Wilson loop (or straight Wilson line) and a local operator in ABJM theory utilizing its M-theory description. The local operator can be a $1/3$-BPS single-trace chiral primary operator or the stress-energy tensor. Using the AdS/CFT correspondence, these correlators are dual to fluctuations of a probe M2-brane in $AdS_4 \times S^7/\mathbb{Z}_k$. We derive analytic results for both cases and compare them with existing results based on supersymmetric localization in the literature. In the large-$N$ limit with $k$ finite, our holograkphic results exhibit perfect agreement with localization.

hep-th↗

arXiv2025

Mesons in a quantum Ising ladder

When two transverse-field Ising chains (TFICs) with magnetic order are coupled, the original free excitations become confined, giving rise to meson-like bound states. In this work, we study such bound states systematically. The mesons are characterized by their fermion number parity and chain-exchanging properties, which lead to distinct sets of mesonic states. The meson masses are determined by solving the Bethe-Salpter equation. An interesting observation is the additional degeneracy in the chain-exchanging odd sectors. Beyond the two particle approximation, we exploit the truncated free fermionic space approach to calculate the spectrum numerically. Corrections to the meson masses are obtained, and the degeneracy is further confirmed. The characterization and degeneracy can be connected to the situation when each chain is tuned to be quantum critical, where the system is described by the Ising$_h^2$ integrable model, a sine-Gordon theory with $\mathbb{Z}_2$ orbifold. Here we establish a clear correspondence between the particles in the bosonized form and their fermionic counterparts. Near this point, the stability of these particles is analyzed using the form factor perturbation scheme, where four particles are always present. Additionally, we calculate the evolution of the dominant dynamical structure factor for local spin operators, providing further insight into the low-energy excitations and their role in the system's behavior. The two-particle confinement framework as well as the parity classifications may inspire the study for other coupled bi-partite systems.

hep-th↗

arXiv2025

Spin dynamics and dark particle in a weak-coupled quantum Ising ladder with $\mathcal{D}_8^{(1)}$ spectrum

Emergent Ising$_h^2$ integrability is anticipated in a quantum Ising ladder composed of two weakly-coupled critical transverse field Ising chains. The system is remarkable for including eight types of massive relativistic particles, with their scattering matrix and mass spectrum characterized by the $\mathcal{D}_8^{(1)}$ Lie algebra. In this article, by computing the spin dynamical structure factors following analytical form factor approach, we clearly identify dispersive single-particle excitations of (anti-) soliton and breathers as well as their multi-particle continua in the spectra, which is further confirmed by the numerical simulations. We show that the selection rule inherent in the parity and topological charge of the theory, causes a significant result that charge-parity-odd particles, termed as dark particles, cannot be directly excited from the ground state through any local or quasi-local operations. This in turn suggests the long lifetime of the lightest dark particle.

cond-mat.str-el↗