Searcharxiv⌕ Search

arXiv subjects

Song He

Publications and source records attributed to Song He.

At least 19 recordsLinked to original sources
arXiv2026

Simplicity of the three-point stress-tensor form factor beyond the planar limit

We express the complete three-loop subleading-color finite remainder of the three-point stress-tensor-multiplet form factor in $\mathcal N=4$ super Yang--Mills theory as a permutation sum of a single $A_2$-type function. The non-product part of the seed is a combination of 35 weight-six generalized polylogarithms, while all lower-weight products and zeta-value terms belong to the same five-letter algebra. A bootstrap based on independently computed collinear data, branch-cut constraints and empirical final-entry relations determines both the symbol and the full function. The remaining function-level ambiguity is proportional to $ζ_2$ times the two-loop planar remainder and is fixed by a single final-entry relation. The weight-three left coproduct factors of the planar and subleading-color results span the same space modulo products; at weight four, the subleading-color result contains four additional nonclassical directions. Through the established maximal-transcendentality correspondence, this compact representation also describes the weight-six subleading-color sector of Higgs-plus-three-gluon amplitudes in QCD. We also construct a four-loop candidate symbol space under a conjectural extension of the three-loop constraints.

hep-th↗
arXiv2026

All-plus Yang--Mills and gravity wavefunctions in de Sitter space

We present sewing representations for tree-level all-plus wavefunctions in four-dimensional de Sitter space. For Yang--Mills theory, the arbitrary-multiplicity formula is a sum over noncrossing polygon dissections, with each cell carrying energy differences of a full lower-point wavefunction. The absence of a generic total-energy pole is manifest, while partial-energy residues are determined by the lower-point factors. We derive this representation from self-dual Yang--Mills solutions. For Einstein gravity, we propose an arbitrary-multiplicity formula consisting of an alternating sum over labelled sewing trees plus a local gravitational Chern--Simons term. This local term arises from the self-dual Einstein action and supplies boundary data not fixed by internal-energy cuts. We derive a generating formula for it from the boundary connection and give explicit expressions through seven points.

hep-th↗
arXiv2026

A periodic $\bar q$ equation for form factors

MHV form factors of the chiral stress-tensor multiplet in planar $\mathcal N=4$ super Yang-Mills theory are dual to periodic null Wilson loops. We propose a periodic $\bar q$ equation for the MHV and higher-helicity sectors at vanishing fermionic monodromy. The equation relates kinematic derivatives of $\mathrm N^k\mathrm{MHV}$ form factors to collinear integrals of $\mathrm N^{k+1}\mathrm{MHV}$ form factors with one additional external particle, providing a recursive relation in loop order. In periodic momentum supertwistors, it has the same collinear-integral form as the two dotted components of the amplitude $\bar Q$ equation, with coefficient $Γ_{\rm cusp}/4$, despite the absence of ordinary dual conformal invariance at fixed operator momentum. For parity-even scalar MHV remainders, combining the equation with its parity image supplies all directions of the kinematic differential. We verify the equation analytically for the one-loop four-point NMHV form factor and reconstruct the two-loop three-point MHV remainder at function level. Further two-loop MHV tests give numerical agreement with derivatives of the known four-point remainder at a fixed kinematic configuration, and for five points, all six chiral derivatives agree exactly at symbol level for a one-parameter family of kinematics. The structure of the collinear source further gives all-loop predictions for MHV last entries, consistent with known results and form a space of dimension $n(2n-5)$. The periodic Wilson-loop picture also motivates an all-loop derivation. Using the form-factor OPE, we extract the one-loop correction to the fermion energy from the logarithmic source and recover its vanishing at zero momentum.

hep-th↗
arXiv2026

String Amplitudes on Integer Rectangles

Hidden zeros of tree-level string amplitudes of colored scalars lie on loci specified by integer-valued dimensionless momentum contractions arranged in rectangles on the kinematic mesh. We study the same kinematic loci for open-string amplitudes with gluons, fermions and higher-spin states at arbitrary finite mass levels. Disk monodromy relations yield $\textit{zero-locus factorization}$: at regular points where the monodromy system is invertible, the amplitude is a weighted sum of physical three-point amplitudes sewn to complete on-shell $(n-1)$-point amplitudes. Hidden zeros follow when the external wavefunctions annihilate all contributing three-point couplings. In the low-energy limit, the massless zero-integer branch recovers the corresponding field-theory factorization. For closed strings, including gravitons, persistent cubic zeros in both chiral sectors remove the disk poles, allowing the Kawai--Lewellen--Tye momentum-kernel zero to imply amplitude zeros. The operator product expansions of external vertices give a common worldsheet origin for these conditions across spins and mass levels.

hep-th↗
arXiv2026

Exact stress-tensor generators distinguish integrable continuations

The same leading $T\bar T$ interaction can coexist with sharply different strong-field responses, even within causal, classically integrable sigma models. We reconstruct exact autonomous stress-tensor generators for prescribed one-scale Courant--Hilbert families in two dimensions. Separating the invariant stress scale from a signed trace ratio reduces reconstruction to one scalar inversion on each invertible physical branch. The resulting profile determines both the deformation law and the relation between local energy density and pressure. For generalized Born--Infeld and logarithmic models, the leading interactions coincide, yet pressure saturates in the former and grows without bound in the latter. Their exact generators are respectively quadratic and nonpolynomial, the latter involving Lambert $W_{-1}$. A regular Legendre transformation gives the same profile in the auxiliary potential formulation. The flows commute locally with root-$T\bar T$ within a common smooth branch and retain a common classical Lax form. Exact reconstruction thus quantifies the nonlinear freedom left by leading-order matching.

hep-th↗
arXiv2026

All-Plus QED Wavefunctions in de Sitter Space

We present a compact all-multiplicity formula for tree-level late-time wavefunction coefficients of scalar QED in four-dimensional de Sitter space, with a conformally coupled charged scalar pair and positive-helicity photons. The result admits both a recursive representation in terms of shifted lower-point coefficients and an explicit finite sum involving only kinematic factors. The flat-space amplitudes vanish for two or more photons, yet the de Sitter coefficients remain nonzero. These zeros enforce cancellations of the total-energy residue and, through factorization, of proper partial-energy residues involving multi-photon subamplitudes. Using a common-reference construction, we derive an exact lower-point recursion from Abelian Ward identities. Conformal symmetry provides an independent check: the partition sum solves the inhomogeneous Ward identity, while the total-energy term is a homogeneous solution. We also outline an analogous recursion in massless fermionic QED.

hep-th↗
arXiv2026

Planar loop integrands from cuts in $D$ dimensions

We present a direct reconstruction formula for planar loop integrands from $D$-dimensional generalized unitarity cuts in any colored theory. The reconstruction combinatorics is separated from the theory-dependent tree amplitudes entering the cuts: for the $L$-loop $n$-point color-ordered amplitude, the integrand is expressed as a sum over admissible non-scaleless scalar graphs dressed by corresponding cuts in $D$ dimensions; the coefficients are given by the universal Möbius-inversion formula of the refinement poset, or equivalently one minus the Euler characteristics of associated complexes. As an application we write down closed-formulas for loop integrands in pure Yang--Mills theory, where the required cuts are generated by gluing $D$-dimensional tree amplitudes and summing over internal gluon states. We also use the two-loop five-point case as a validation, comparing with known integrand data and after integration-by-parts reduction, with known integrated helicity amplitudes. The same framework also produces compact cut-organized data for larger examples, including the two-loop six-point and three-loop four-point cases. We also describe the corresponding simplification in maximally supersymmetric Yang--Mills theory, where the absence of bubble and triangle subgraphs reduces the relevant cut poset substantially.

hep-th↗
arXiv2026

A new product entropy

We propose a new product entropy, defined as the Rényi (or von Neumann) entropy of a normalized product operator constructed from two density matrices. We establish a duality showing that the SVD entanglement entropy of a subsystem for two pure states is exactly equivalent to the product entropy of the complementary subsystem. This connection provides both a transparent physical interpretation in terms of the spectral diversity of the subsystem state product and a computationally efficient route that bypasses the reduced transition matrix. For low-lying eigenstates, we derive analytical expressions for the subsystem product entropy between the ground state and primary excitations in two-dimensional conformal field theories, explicitly verified against the critical Ising chain. In quantum quench dynamics, the quasiparticle picture yields time evolution in the scaling limit: following a global quench, the subsystem product entropy exhibits distinct sequences of thermalization and revivals, whereas under a local operator quench, it develops characteristic plateaus whose constant values are determined by the inserted operator. Extensive numerical calculations on the critical Ising chain confirm the analytical predictions with excellent accuracy.

hep-th↗
arXiv2026

Form Factor Alphabets and Antipodal Duality from Cluster Algebras

We develop a cluster-algebraic description of symbol alphabets for chiral stress-tensor form factors in planar $\mathcal N=4$ super-Yang--Mills theory. Motivated by unfolding the three-point $C_2$ quiver, we propose a periodic framework for $n$-point form-factor alphabets based on folding a $\mathrm{Gr}(4,2n)$ quiver with two periods of frozen nodes. At four points, the folding leads to the $\widetilde{\mathrm{VI}}$ cluster algebra, which has infinitely many cluster variables. Tropical truncation selects a finite set of rational coordinates and four physical limit rays. The $A_1^{(1)}$ mutation sequences approaching these rays generate the four square roots and the corresponding algebraic-letter spaces. Within the resulting finite set of rational candidates, antipodal closure excludes precisely eight additional letters. On the parity-preserving surface, the antipodal map is realized, after a further folding, by two commuting mutations followed by a relabelling. Furthermore, we find an alternative quiver within the same mutation class that becomes self-antipodal after parity folding, mirroring the antipodal self-duality of the four-point MHV form factor. Its double- and triple-collinear boundaries reproduce, respectively, the $C_2$ algebra of the three-point form factor and the $A_3$ algebra of the six-point amplitude; after folding the latter to $C_2$, the antipodal map exchanges the two $C_2$ boundaries.

hep-th↗
arXiv2026

Bootstrapping Giant Graviton Correlators

We develop bootstrap methods for mixed heavy-light four-point correlators $\langle GGOO\rangle$ in $\mathcal N=4$ super-Yang--Mills theory at large $N$, where $O\equiv {\cal O}_2$ is the chiral primary operator in the stress-tensor multiplet and $G$ are (dual) giant graviton operators with dimension of order $N$, including the maximal determinant case. The loop integrand is expanded in a basis of labelled $f$-graphs -- necessarily including non-planar topologies due to the dimension-$N$ nature of the giant gravitons -- and the coefficients are fixed by various bootstrap conditions including double-triangle and triangle rules in the cusp and OPE limits, integrated correlators from supersymmetric localization, and a ten-dimensional hidden symmetry, the latter also allowing extension to correlators involving generic chiral primaries $\mathcal{O}_k$. Together, these inputs uniquely determine the correlator through three loops, passing further non-trivial consistency checks. For the maximal determinant operator, we reproduce the known results through two loops and obtain the full three-loop correction.

hep-th↗
arXiv2026

The Hydrotope in the Water-Wave Action

The Hydrotope gives a geometric representation of tree-level water-wave amplitudes with two negative spatial momenta as the volume of a hyperplane slice of a box. We trace the origin of this geometry directly to the water-wave action. Writing the $n$-point contact interaction as $\mathcal{V}_n=\sum_{i<j}w_iw_jh_{ij}^{(n)}$, we show that when the two marked momenta have the same sign and every spectator has the opposite sign, the corresponding coefficient is $h_{ij}^{(n)}=2H_n$, where $H_n/(n{-}3)!$ is the Hydrotope volume. More generally, every fixed-pair coefficient admits a denominator-free ordered-flag representation as an oriented sum of $(n{-}3)$-dimensional box volumes. We then sum all two-minus trees by cutting each at the unique vertex joining its two minus branches. The coefficients multiplying minus-minus, minus-plus, and plus-plus frequency bilinears reduce, respectively, to $(2^{n{-}1}{-}2)H_n$, $0$, and $2H_n$, and immediately reproduce the known amplitude $2^{n{-}1}w_1w_2H_n$. Thus, the Hydrotope-and a broader class of related box-slice geometries-is already encoded locally in the water-wave action. This points to further hidden simplicity and geometric structure in general water-wave amplitudes.

hep-th↗
arXiv2026

Tropical and Stringy Integrals for In-In Correlators

We introduce tropical and stringy integrals for fixed-graph contributions to cosmological in-in correlators of conformally coupled scalars. The full-time representation factorizes into a graph-dependent vertex-space Laplace integral, with one real variable for each graph vertex, and an elementary edge-space Laplace integral, with one real variable for each internal edge. The vertex-space exponent is a sum of absolute values associated with sites and relative edge times; as a piecewise-linear function, it is the support function of the in-in zonotope. Each absolute value is also the tropical limit of a positive Laurent binomial. Retaining these binomials before tropicalization defines a finite-$α'$ vertex-space stringy integral, so both the polytope and its stringy integral are read directly from the physical time integral. In the $α' \to 0$ limit this integral becomes the normalized dual volume of the in-in zonotope, while the edge-space factor deforms independently into a product of beta integrals and restores the elementary propagator normalization. We derive the field-theory rational form from augmented-graph chambers, as well as exact finite-$α'$ parallel-edge reduction, factorization formulas for edge-energy and partial-energy poles, and even descendant towers. As an alternative geometric realization of fixed-graph correlators, we find an ambient Minkowski-sum and stringy-integral realization of the graph correlahedron for a tree graph as the so-called graph cubeahedron of its line graph. For completeness, we also record the logarithmic critical equations and generic reference degrees of the associated affine divisor arrangement.

hep-th↗
arXiv2026

Emergent gravitational action from non-local $T\bar T$-like deformations

We study the gravitational effective action induced, at first order in the deformation parameter, by non-local $T\bar T$-like deformations of quantum field theories. Using a heat-kernel formulation, we extract the local geometric terms generated by stress-tensor two-point functions, and apply the construction to free fermions, massive Maxwell theory, and second-order Yang-Mills theory. While the resulting coefficients are generally model dependent, conformal field theories contain a universal sector fixed by the central charge $C_T$. After regularization and renormalization, this sector yields finite, scheme-independent contributions organized into a finite set of curvature invariants. We further analyze trace-trace deformations, for which the relevant contact terms are determined by the Weyl anomaly, and derive the corresponding finite gravitational action for a general class of minimal non-local kernels. These results provide a quantum effective-action realization of induced gravity in which universal conformal data determine calculable contributions to the emergent geometric response.

hep-th↗
arXiv2026

Timelike Entanglement First Law and Linearized Field Equations in Higher Curvature Gravity

We investigate the timelike entanglement first law in holographic conformal field theories whose bulk dual is Lovelock gravity. Using the double Wick rotation formulation of timelike entanglement entropy together with the Jacobson-Myers entropy functional, we compute the linear variation of holographic timelike entanglement entropy for hyperbolic subregions. For cubic Lovelock gravity, we explicitly show that a single, universal multiplicative renormalization factor governs how higher curvature interactions enter the variations of both the entropy and the modular Hamiltonian, leading to $ΔS=Δ\langle H\rangle$ for low-energy thermal excitations. We then extend the analysis to Lovelock gravity of arbitrary order around the anti-de Sitter spacetime in the Fefferman-Graham gauge. For normalizable perturbations, the variation of the Jacobson-Myers functional reduces to the Einstein gravity's result multiplied by the same coupling-dependent factor that renormalizes the effective Newtonian constant in the linearized field equations of Lovelock gravity. We further show that the boundary contribution vanishes in the conformal limit for the class of perturbations considered. Consequently, the timelike entanglement first law is equivalent to the linearized field equations of Lovelock gravity about the maximally symmetric background, within the hyperbolic and perturbative regime considered in the present paper.

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

Operational Tube-Sector Theory of Quantum State Distinguishability Under Generalized Symmetries

A variational principle for quantum-state distinguishability is established in many-body systems with generalized symmetries, including noninvertible cases described by fusion categories. Standard fidelity and symmetry-resolved diagnostics emerge as coarse-grained limits of a more refined operational structure. When symmetry actions terminate at entanglement cuts, distinguishability is governed by boundary tube algebras within a symmetry-constrained measurement resource theory. The physically admissible instruments are characterized by complete positivity, entanglement-cut locality, boundary-module covariance, and sequential stability. The resulting optimal measurement structure is uniquely fixed by the center of the boundary tube algebra, $\mathcal{A}_{\mathrm{phys}} = Z\!\left(\mathrm{Tube}_{\mathcal{C}}(\mathcal{M}_A)\right)$, whose primitive dempotents define tube-sector probabilities that refine fidelity-based and symmetry-resolved descriptions. The associated tube positive-operator-valued measures (POVMs) are extremal and yield optimal one-shot hypothesis-testing distinguishability under symmetry constraints. The categorical selection rule is universal across fusion categories and independent of microscopic realization; microscopic models enter by choosing the boundary module and the protocol family used to witness a nontrivial tube fiber.

hep-th↗
arXiv2026

Bootstrapping the Four-Point NMHV Stress-Tensor Form Factor

We bootstrap the four-point next-to-maximally helicity-violating (NMHV) form factor of the chiral stress-tensor supermultiplet in planar maximally supersymmetric Yang-Mills theory through three loops at the symbol level. At two loops, an ansatz built from NMHV leading singularities and the relevant five-point one-mass integral function space is fixed uniquely by physical constraints; the resulting ratio function symbol contains 78 letters, all drawn from the 88-letter alphabet previously identified in the four-point MHV sector. At three loops, using this 88-letter alphabet as input and imposing extended Steinmann relations satisfied by the minimally-subtracted hard function, together with other physical constraints, we determine the three-loop symbol uniquely. Both results pass soft, double-soft and directional dual conformal invariance (DDCI) checks, provide the first multi-loop non-MHV form-factor data, and support the universality of the 88-letter alphabet for four-point form factors beyond the MHV sector.

hep-th↗
arXiv2026

Exact Relevant Stress-Tensor Flows and a Causality No-Go in Self-Dual Electrodynamics

Can a classically relevant stress-tensor deformation be exactly solvable, duality preserving, and physically causal? We construct an exact power-law family of nonlinear electrodynamics preserving electromagnetic duality, together with a parallel two-dimensional Lax-integrable realization. Its auxiliary geometry yields the full characteristic-cone phase diagram and a universal finite-energy fold. For the Maxwell seed, every nonzero relevant branch is acausal, whereas every causal branch is caustic-free; undeformed Maxwell theory is the only causal point in the relevant regime.

hep-th↗