arXiv subjects

Song He

Publications and source records attributed to Song He.

At least 55 records · Page 3Linked to original sources

arXiv2025

Character of the highest weight module of BMS algebra realized on codimensional-two boundary

In this paper, we investigate the highest weight representation (HWR) of the three and four-dimensional Bondi-Metzner-Sachs (BMS) algebra realized on the codimension-two boundary of asymptotic flat spacetime (AFS). In such a realization, the action of supertranslation shifts the conformal weight of the highest-weight states. As a result, there is no extra quantum number relating to the supertranslation. We construct the highest-weight BMS modules and compute their characters. We show that the BMS$_3$ highest-weight vacuum character with special value of central charges coincides with the 1-loop partition function of three-dimensional asymptotic flat gravity, up to an overall phase factor ``$i$''. We expect the vacuum character of BMS$_4$ may shed light on the flat holography in four dimensions.

hep-th↗

arXiv2025

Heptagon Symbols at Five Loops and All-Loop Sequences

We revisit the symbol bootstrap program for the seven-particle MHV and NMHV amplitudes in planar $\mathcal{N}=4$ super-Yang-Mills (SYM) based on the alphabet associated with the $E_6$ cluster algebra. After imposing integrability, cluster adjacency (or extended Steinmann), first- and last-entry conditions, the solution space is already highly restrictive: e.g. for MHV case there are exactly $1,1,2,3,4$ parity-invariant solutions for $L=1,2,\cdots, 5$, which automatically satisfy dihedral symmetry. Remarkably, after further requiring a well-defined collinear limit, we find a unique solution for both MHV and NMHV sectors where all coefficients (e.g. more than $3.1\times 10^{10}$ for MHV at $L=5$) turn out to be integers. Furthermore, we observe recurrent patterns for coefficients of special words in $E_6$ symbols mirroring those found for the $C_2$ symbol of three-point form factors, which lead to numerous predictions in the form of all-loop sequences. As an initial application, we show that these sequences uniquely fix the MHV symbol through five loops without input from collinear limits. Given the simplicity and surprisingly strong constraining power of both physical constraints and the newly observed sequences, we conjecture that there is a unique symbol satisfying these constraints at any loop order.

hep-th↗

arXiv2025

Superstring amplitudes meet surfaceology

We reformulate tree-level amplitudes in open superstring theory (type-I) in terms of stringy Tr$(ϕ^3)$ amplitudes with various kinematical shifts in the "curve-integral" formulation: while the bosonic-string amplitude with $n$ pairs of "scaffolding" scalars comes from a particularly simple shift of the Tr$(ϕ^3)$ one (corresponding to $n$ length-$2$ cycles), the analogous superstring amplitude requires "correction" terms given by bosonic-string amplitudes with longer, even-length "cycles", which are also Tr$(ϕ^3)$ ones at shifted kinematics dictated by the cycles; in total it is expressed as a sum of $(2n{-}3)!!$ shifted amplitudes originated from the expansion of a reduced Pfaffian. Upon taking $n$ scaffolding residues, this leads to a new formula of the $n$-gluon superstring amplitude, which is manifestly symmetric in $n{-}1$ legs, as a gauge-invariant combination of mixed bosonic string amplitudes with gluons and scalars, which come from length-$2$ cycles and longer ones respectively (the total sum is associated with the expansion a $n\times n$ symmetrical determinant); the corresponding prefactors are nested commutators of $2n$-gon kinematical variables, which nicely become traces of field-strengths for those legs corresponding to scalars in the mixed amplitudes. These interesting linear combinations of bosonic string amplitudes must guarantee the cancellation of tachyon poles and $F^3$ vertices ${\it etc.}$, and they give new relations between the superstring amplitude and its bosonic-string building blocks to all orders in the $α'$ expansion (the first order gives a new formula for gluon amplitudes with a single $F^3$ insertion in terms of Yang-Mills-scalar amplitudes). We provide both the worldsheet and "curve-integral" derivations, and discuss applications to heterotic and type II cases.

hep-th↗

arXiv2025

Notes on conformal integrals: Coulomb branch amplitudes, magic identities and bootstrap

We study multi-loop conformal integrals for four-point correlators of planar ${\cal N}=4$ super-Yang-Mills theory, and in particular those contributing to Coulomb branch amplitudes in the ten-dimensional lightlike limit, where linear combinations of such integrals are determined by the large R-charge octagons exactly known from integrability. Exploiting known results for integrands, we review those combinations of dual conformal invariant (DCI) integrals that must evaluate to determinants of ladders, generalizing the simplest cases of Basso-Dixon fishnet integrals; in this way, we summarize all-loop predictions for the integrands (which are extracted from $f$-graphs) contributing to components of Coulomb branch amplitudes, such as next-to-fishnet integrals. Moreover, this exercise produces new ``magic identities", {\it i.e.} certain combinations of DCI integrals equal zero, and we enumerate and simplify such identities up to six loops explicitly. On the other hand, most of these individual integrals have not been computed beyond three loops, and as a first step we consider a bootstrap program for DCI integrals based on their leading singularities and the space of pure functions. We bootstrap the $3$ non-trivial DCI integrals for four-loop Coulomb branch amplitudes (providing an independent verification of the four-loop magic identity), which all take remarkably simple form as weight-$8$ single-valued harmonic polylogarithms. We also compute all leading singularities and a large portion of the pure functions for the $34$ DCI integrals contributing to five-loop amplitudes, where not only some integrals evaluate to functions beyond harmonic polylogarithms but they also contain lower-weight pieces individually.

hep-th↗

arXiv2025

Loop-Level Double Copy Relations from Forward Limits

We study double copy relations for loop integrands in gauge theories and gravity based on their constructions from single cuts, which are in turn obtained from forward limits of lower-loop cases. While such a construction from forward limits has been realized for loop integrands in gauge theories, we demonstrate its extension to gravity by reconstructing one-loop gravity integrands from forward limits of trees. Under mild symmetry assumptions on tree-level kinematic numerators (and their forward limits), our method directly leads to double copy relations for one-loop integrands: these include the field-theoretic Kawai-Lewellen-Tye (KLT) relations, whose kernel is the inverse of a matrix with rank $(n{-}1)!$ formed by those in bi-adjoint $ϕ^3$ theory, and the Bern-Carrasco-Johansson (BCJ) double copy relations with crossing-symmetric kinematic numerators (we provide local and crossing-symmetric Yang-Mills BCJ numerators for $n=3,4,5$ explicitly). By exploiting the "universal expansion" for one-loop integrands in generic gauge theories, we also obtain an analogous expansion for gravity (including supergravity theories).

hep-th↗

arXiv2025

Detecting quantum chaos via pseudo-entropy

Quantum informatic quantities such as entanglement entropy are useful in detecting quantum phase transitions. Recently, a new entanglement measure called pseudo-entropy was proposed which is a generalization of the more well-known entanglement entropy. It has many nice properties and is useful in the study of post-selection measurements. In this paper, one of our goals is to explore the properties of pseudo-entropy and study its effectiveness as a quantum chaos diagnostic, i.e., as a tool to distinguish between chaotic and integrable systems. Using various variants of the SYK model, we study the signal of quantum chaos captured in the pseudo-entropy and relate it to the spectral form factor (SFF) and local operator entanglement (LOE).

hep-th↗

arXiv2025

Generalized $T\overline{T}$-like Deformations in Duality-Invariant Nonlinear Electrodynamic Theories

This study introduces a high-order perturbation methodology to categorize two primary solution types within duality-invariant nonlinear electrodynamic theories, adhering to the differential self-duality criterion. The first solution type aligns with irrelevant stress tensor flows, resembling $T\bar{T}$ dynamics, and the second involves a blend of irrelevant $T\bar{T}$-like and marginal root-$T\bar{T}$-like deformations. Our approach facilitates the investigation of diverse duality-invariant nonlinear electrodynamics theories and their stress tensor flows and confirms the commutativity of flows initiated by irrelevant and marginal operators.

hep-th↗

arXiv2025

Generalized $T\bar{T}$-like flows for scalar theories in two dimensions

We demonstrate that the necessary condition for $SO(N) \times SO(N)$ duality invariance manifests as a partial differential equation in two-dimensional scalar theories. This condition, expressed as a partial differential equation, corresponds precisely to the integrability condition. We derive a general perturbation solution to this partial differential equation, which includes both a root $T\bar{T}$ flow equation and an irrelevant $T\bar{T}$-like flow equation. Additionally, we identify a general form for these flow equations that commute with each other. Our results establish a general integrable theory characterized by theory-dependent coefficients at each order in the $λ$-expansion. This unified framework systematically classifies all integrable theories possessing two Lorentz-invariant variables ($P_1$, $P_2$) while accommodating arbitrary orders of the coupling constants ($λ$, $γ$). The theory provides a comprehensive classification scheme that encompasses both known and novel integrable systems within this class.

hep-th↗

arXiv2025

Root-$T\bar{T}$ Deformations on Causal Self-Dual Electrodynamic Theories

The self-dual condition, which ensures invariance under electromagnetic duality, manifests as a partial differential equation in nonlinear electromagnetism theories. The general solution to this equation is expressed in terms of an auxiliary field, $τ$, and Courant-Hilbert functions, $\ell(τ)$, which depend on $τ$. Recent studies have shown that duality-invariant nonlinear electromagnetic theories fulfill the principle of causality under the conditions $\frac{\partial \ell}{\partial τ} \ge 1$ and $\frac{\partial^2 \ell}{\partial τ^2} \ge 0$. In this paper, we investigate theories with two coupling constants that also comply with the principle of causality. We demonstrate that these theories possess a new universal representation of the root-$T\bar{T}$ operator. Additionally, we derive marginal and irrelevant flow equations for the logarithmic causal self-dual electrodynamics and identify a symmetry referred to as $α$-symmetry, which is present in all these models.

hep-th↗

arXiv2025

Thermodynamic topology of Einstein-Maxwell-Dilaton Theories

We present a systematic investigation of the thermodynamic topology for a broad class of asymptotically charged Anti-de Sitter (AdS) black holes in Einstein-Maxwell-Dilaton (EMD) theories, examining how scalar coupling parameters and spacetime dimensions influence black hole thermodynamics. Employing a topological approach that utilizes the torsion number of vector fields constructed from the generalized free energy, we characterize black hole states as topological defects within the thermodynamic parameter space. Through analytical solutions spanning dimensions $d = 4$, $d=5$, and $d=6$, including the Gubser-Rocha model, we demonstrate that variations in the dilaton coupling constant $δ$, particularly near its critical value $δ_c$, induce transitions between distinct thermodynamic topological phases. Our analysis reveals that certain black hole solutions constitute a novel class designated as $W^{0-\leftrightarrow 1+}$, characterized by a torsion number $W = 1$ that corresponds to a unique stability structure. We establish that Gubser-Rocha models belong to this topological classification. These results significantly expand the existing classification framework while reinforcing thermodynamic topology as a robust analytical tool for probing the universal properties of black holes in both gravitational and holographic contexts. The findings provide new insights into the relationship between microscopic couplings and macroscopic thermodynamic behavior in extended gravity theories.

hep-th↗

arXiv2025

Constructibility of AdS supergluon amplitudes

We prove that all tree-level $n$-point supergluon (scalar) amplitudes in AdS$_5$ can be recursively constructed, using factorization and flat-space limit. Our method is greatly facilitated by a natural R-symmetry basis for planar color-ordered amplitudes, which reduces the latter to "partial amplitudes" with simpler pole structures and factorization properties. Given the $n$-point scalar amplitude, we first extract spinning amplitudes with $n{-}2$ scalars and one gluon by imposing "gauge invariance", and then use a special "no-gluon kinematics" to determine the $(n{+}1)$-point scalar amplitude completely (which in turn contains the $n$-point single-gluon amplitude). Explicit results of up to 8-point scalar amplitudes and up to 6-point single-gluon amplitudes are included as Supplemental Material.

hep-th↗

arXiv2025

A Hidden Permutation Symmetry of Squared Amplitudes in ABJM Theory

We define the square amplitudes in planar Aharony-Bergman-Jafferis-Maldacena theory (ABJM), analogous to that in $\mathcal{N}{=}4$ super-Yang-Mills theory (SYM). Surprisingly, the $n$-point $L$-loop integrands with fixed $N{:=}n{+}L$ are unified in a single generating function. Similar to the SYM four-point half-BPS correlator integrand, the generating function enjoys a hidden $S_N$ permutation symmetry in the dual space, allowing us to write it as a linear combination of weight-3 planar $f$-graphs. Remarkably, through Gram identities it can also be represented as a linear combination of bipartite $f$-graphs which manifest the important property that no odd-multiplicity amplitude exists in the theory. The generating function and these properties are explicitly checked against squared amplitudes for all $n$ with $N{=}4,6,8$. By drawing analogies with SYM, we conjecture some graphical rules the generating function satisfy, and exploit them to bootstrap a unique $N{=}10$ result, which provides new results for $n{=}10$ squared tree amplitudes, as well as integrands for $(n,L){=}(4,6),(6,4)$. Our results strongly suggest the existence of a "bipartite correlator" in ABJM theory that unifies all squared amplitudes and satisfies physical constraints underlying these graphical rules.

hep-th↗

arXiv2025

Hydrodynamical transports in generic AdS Gauss-Bonnet-scalar Gravity

The experimentally observed temperature-dependent shear and bulk viscosities of the quark-gluon plasma (QGP), along with its apparent violation of the Kovtun-Son-Starinets (KSS) bound $η/s=1/(4π)$, necessitate a holographic description that incorporates higher-derivative corrections. We propose a five-dimensional Einstein-Scalar-Maxwell-Gauss-Bonnet model in which a scalar-Gauss-Bonnet coupling $H(ϕ)$ encodes leading curvature corrections. Although no closed-form black hole solution is available, we employ an entropy-production analysis at the event horizon to derive exact analytic formulas for the shear viscosity $η$ and bulk viscosity $ζ$. These expressions exhibit apparent deviation from the KSS bound and nontrivial temperature dependence. We then perform an independent computation via the retarded Green function (Kubo) method, finding perfect agreement for $η$ and isolating a single constant in $ζ$ that requires numerical determination. Our dual derivation underscores the pivotal role of higher-derivative terms in realistic QGP modeling and demonstrates the efficacy of nonanalytic holographic backgrounds in capturing the dynamics of strongly coupled fluids.

hep-th↗

arXiv2025

Root-$T\bar{T}$ Flows Unify 4D Duality-Invariant Electrodynamics and 2D Integrable Sigma Models

We present a unified framework that connects four-dimensional duality-invariant nonlinear electrodynamics and two-dimensional integrable sigma models via the Courant-Hilbert and new auxiliary field formulations, both governed by a common generating function and a generating potential, respectively. Introducing two commuting deformation parameters, $λ$ (irrelevant) and $γ$ (marginal), we identify a universal class of $γ$-flows, including the root-$T\bar{T}$ deformation and its rescaled variants. Our approach generalizes conventional single-coupling structures via novel field transformations that extend to a two-parameter space ($λ$,$γ$) while preserving the root-$T\bar{T}$ flow condition for all $γ$-coupled theories. We construct several integrable models, including generalized Born-Infeld, logarithmic, q-deformed, and a new closed-form theory applicable to both electrodynamics and integrable systems. This unified framework, based on the unique form of the root-$T\bar{T}$ flow, systematically spans duality-invariant nonlinear electrodynamics in 4D and their exact 2D integrable counterparts.

hep-th↗

arXiv2025

Systematic approach to correlators in $T\bar{T}$ deformed CFTs

We investigate higher-order corrections to correlators in a general CFT (conformal field theory) with the double-trace $T\bar{T}$ deformation. Standard perturbation theory proves inadequate for this problem due to the intricate stress-tensor flow induced by the deformation. To tackle this challenge, we introduce a novel technique termed the conservation equation method. This method leverages the stress tensor's trace relation and conservation property to establish relationships between higher and lower-order corrections, and subsequently determine the correlators by enforcing symmetry properties. As an illustration, we compute first- and higher-order corrections to various types of correlators. Our results align with existing calculations in the literature and demonstrate the viability of our method for general CFTs.

hep-th↗

arXiv2025

Shear transport in far-from-equilibrium isotropization of supersymmetric Yang-Mills plasma

We holographically study the far-from-equilibrium isotropization dynamics of the strongly coupled $\mathcal{N}=4$ supersymmetric Yang-Mills plasma. The dual gravitational background is driven to be out of equilibrium and anisotropic by a time-dependent change in boundary conditions. At late times, the system relaxes and asymptotically approaches a static configuration. The large initial energy densities accelerate the isotropization significantly compared to the initial geometry corresponding to the supersymmetric Yang-Mills vacuum. We analyze shear transport during isotropization by directly computing the time-dependent stress tensor, which is now a nonlinear function of the shear rate. The shear viscosity far from equilibrium displays much richer dynamics than its near-equilibrium counterpart. Moreover, we uncover that the equilibrium viscosity-to-entropy ratio at late times depends on the details of the quench function and the initial data, which could be due to a resummation of the hydrodynamic description. In particular, this ratio can be parametrically smaller than the Kovtun-Son-Starinets bound calculated from linear response theory.

hep-th↗

arXiv2025

Holographic $T\bar{T}$ deformation of the entanglement entropy in (A)dS$_3$/CFT$_2$

In recent years, the holographic duality between $T\bar{T}$-deformed conformal field theory (CFT) and Anti-de Sitter (AdS) spacetime with finite radial cutoff has received significant attention. The study of $T\bar{T}$ deformation within the framework of de Sitter (dS)/CFT duality has also progressed. This paper shows that the trace flow equation in dS spacetime can be analytically extended from its AdS counterpart through double Wick rotations. Meanwhile, we generalize the replica method in both AdS and dS holography to derive a general expression for the entanglement entropy of arbitrary single spatial intervals within the $T\bar{T}$-deformed framework. For both finite size and finite temperature systems, we obtain the analytical expression for the entanglement entropy after $T\bar{T}$ deformation. Finally, in dS/dS holography and half-dS holography, we find that the dual field theory exhibits non-locality by analyzing the strong subadditivity and boosted strong subadditivity of entanglement entropy.

hep-th↗

arXiv2025

Bootstrapping form factor squared in ${\cal N}=4$ super-Yang-Mills

We propose a bootstrap program for the {\it form factor squared} with operator ${\rm tr}(ϕ^2)$ in maximally supersymmetric Yang-Mills theory in the planar limit, which plays a central role for perturbative calculations of important physical observables such as energy correlators. The tree-level $N$-point form factor (FF) squared can be obtained by cutting $N$ propagators of a collection of two-point ``master diagrams" at $(N{-}1)$ loops: for $N=3,4,5,6$ there are merely $1, 2, 4, 13$ topologies of such diagrams respectively, and their numerators are strongly constrained by power-counting (including ``no triangle" property) and other constraints such as the ``rung rule". Moreover, these two-point diagrams provide a ``unification" of FF squared at different numbers of loops and legs, which is similar to extracting (planar) amplitude squared from vacuum master diagrams (dual to $f$-graphs): by cutting $2\leq n<N$ propagators, one can also extract the planar integrand of $n$-point FF squared at $(N-n)$ loops, thus our results automatically include integrands of 2-point (Sudakov) FF up to four loops (where the squaring is trivial), 3-point FF squared up to three loops, and so on. Our ansatz is completely fixed using soft limits of (tree and loop) FF squared and the multi-collinear limit which reduces it to the splitting function, without any other inputs such as unitarity cuts. This method opens up the exciting possibility of a {\it graphical bootstrap} for FF squared for higher $N$ (which contains {\it e.g.} planar Sudakov FF to $N{-}2$ loops) similar to that for the amplitude squared via $f$-graphs. We also comment on applications to the computation of leading order energy correlators where new structures are expected after performing phase-space integrations.

hep-th↗