arXiv subjects

Xinan Zhou

Publications and source records attributed to Xinan Zhou.

At least 19 recordsLinked to original sources

arXiv2026

Pre-Strings Lectures on Holographic Correlators and Analytic Bootstrap

Over the past decade, the bootstrap strategy has transformed the computation of holographic correlators and revealed structures suggesting an emerging scattering amplitude program in AdS. These notes, which are an extended version of the five lectures delivered at the Pre-Strings 2026 School, give a pedagogical introduction and synthesis of these developments. We start with a quick reminder of the essentials of CFT and a brief review of AdS perturbation theory. We then demonstrate in detail the bootstrap strategy for computing holographic correlators in the canonical example 4d $\mathcal{N}=4$ super Yang-Mills theory, at the level of four-point functions and in the regime dual to classical Type IIB supergravity. Several extensions, including higher-point functions, quantum corrections and stringy corrections, are discussed at varying levels of detail. We also explain how the bootstrap strategy can be extended to holographic CFTs with conformal defects, covering a diverse array of different setups.

hep-th↗

arXiv2026

Quantum Gravity Corrections to Giant Graviton Correlators

We compute the leading quantum gravity correction to the correlation function of two maximal giant gravitons and two light supergravitons in the stress tensor multiplet in the supergravity limit of $\mathcal{N}=4$ SYM theory. By viewing the giant gravitons as a zero-dimensional defect, we employ the defect version of the AdS unitarity method to reconstruct the one-loop correction from the known tree-level correlators. We obtain the one-loop result in closed form in both Mellin and position space. We also extract the quantum correction to the anomalous dimension of operators describing a bound state of a giant graviton and a light supergraviton at the leading conformal twist in the defect channel OPE.

hep-th↗

arXiv2026

Cosmological Correlators Using Tensor Networks

We develop a nonperturbative tensor-network framework for computing cosmological correlators in de Sitter space and use it to test the proposal that suitably defined in-in correlators can be obtained from an in-out formalism by gluing the expanding and contracting Poincaré patches. Focusing on interacting $1+1$-dimensional $ϕ^4$ theory, we formulate finite-time lattice observables using Matrix Product State (MPS) techniques and analyze the regulator subtleties associated with the singular behavior near the patching surface. Within this regulated framework, we find controlled nonperturbative evidence for the proposed relation between in-in and in-out correlators in several examples. We also find suggestive evidence that the perturbative obstructions present for sufficiently light fields can be softened nonperturbatively, albeit in a regime of substantially larger entanglement. A central outcome of our analysis is an entanglement-based picture of the computation: for in-in evolution the entanglement remains modest and can decrease toward late times, whereas in the patched in-out set-up it grows significantly after the gluing slice. Thus, although the in-out formalism is perturbatively economical, the in-in formulation is numerically more favorable. We briefly discuss how the same strategy extends to low-angular-momentum sectors in $3+1$ dimensions, and why regimes of rapid entanglement growth may eventually motivate quantum-computing implementations.

hep-th↗

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

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

Notes on flat-space limit of holographic defect correlators in position space

We study the large AdS radius limit of correlation functions in holographic defect CFTs. For two-point functions of operators inserted away from the defect, we derive a position space formula relating a certain scaling limit of the correlators to the flat-space scattering form factors. We show that our position space prescription is equivalent to the flat-space limit formula recently conjectured in Mellin space and also test our result in a few nontrivial theories.

hep-th↗

arXiv2025

Unitarity Method for Holographic Defects

We initiate the study of loop-level holographic correlators in the presence of defects. We present a unitarity method which constructs loop corrections from lower order data. As an example, we apply this method to 6d $\mathcal{N}=(2,0)$ theories with $\frac{1}{2}$-BPS surface defects and report the first holographic two-point function at one loop.

hep-th↗

arXiv2025

Dissecting supergraviton six-point function with lightcone limits and chiral algebra

We develop a bootstrap strategy to obtain the six-point function of supergravitons in $AdS_5\times S^5$ from symmetry constraints and consistency conditions. Compared to previous bootstrap algorithms, a novel feature is the use of lightcone OPEs together with the chiral algebra constraint. This makes it possible to isolate different parts of the correlator and fix them separately. Our strategy allows us to gain a refined understanding of the power of different bootstrap constraints, which is also useful for computing more general correlators.

hep-th↗

arXiv2025

One-loop Gluon Amplitudes in AdS

We initiate the study of one-loop gluon amplitudes in AdS space. These amplitudes were recently computed at tree level for a variety of backgrounds of the form $AdS_{d+1} \times S^3$. For concreteness, we compute the one-loop correction to the massless gluon amplitude on $AdS_5\times S^3$, which corresponds to the four-point correlator of the flavor current multiplet in the dual 4d $\mathcal{N}=2$ SCFT. This requires solving a mixing problem that involves tree-level amplitudes of arbitrarily massive Kaluza-Klein modes. The final answer has the same color structure as in flat space but the dependence on Mandelstam variables is more complicated, with logarithms replaced by polygamma functions.

hep-th↗

arXiv2024

Meson correlators in 4d $\mathcal{N}=2$ SCFTs and hints for 8d structures at weak coupling

We study correlators of $\frac{1}{2}$-BPS mesons in two examples of 4d SQCDs with $\mathcal{N}=2$ superconformal symmetry in the planar limit. We focus on the weakly coupled regime and obtain one-loop corrections to $n$-point meson correlators with arbitrary operator dimensions. We show that these corrections can be resumed into generating functions which exhibit emergent 8d structures similar to the ones previously observed at strong coupling via AdS/CFT. These structures of the $\mathcal{N}=2$ theories also resemble the hidden 10d structures in 4d $\mathcal{N}=4$ SYM.

hep-th↗

arXiv2024

Flat-space limit of defect correlators and stringy AdS form factors

We study AdS form factors, given by the Mellin representation for CFT correlators of local operators in the presence of extended defects. We propose a formula for taking (and expanding around) the flat-space limit. This formula relates the flat-space form factors for particles scattering off an extended object to the high-energy limit of the Mellin amplitude, via a Borel transform. We check the validity of our proposal in a number of examples. As an application, we study the two-point function of local operators in the presence of a 't Hooft loop in 4d $\mathcal{N}=4$ SYM, and compute the first few orders of stringy corrections to the AdS form factor of gravitons scattering off a D1 brane.

hep-th↗

arXiv2024

On the Regge behaviour of the AdS Virasoro-Shapiro Amplitude

We compute the AdS Virasoro-Shapiro amplitude in the Regge limit, in terms of the CFT data of the exchanged operators in the leading Regge trajectory. To any order in the small curvature expansion, the result can be written in terms of derivatives of the flat space Virasoro-Shapiro amplitude in the Regge limit. The result also admits an integral representation involving single-valued logarithms, fully consistent with recent proposals for the full AdS Virasoro-Shapiro amplitude.

hep-th↗

arXiv2024

Correlators of $\mathcal{N}=4$ SYM on real projective space at strong coupling

We consider type IIB supergravity on a $\mathbb{Z}_2$ quotient of AdS$_5\times$S$^5$ as the holographic dual of strongly coupled 4d $\mathcal{N}=4$ SYM on $\mathbb{RP}^4$ space with the gauging of charge conjugation. Using bootstrap techniques, we determine all two-point functions of $\frac{1}{2}$-BPS operators of arbitrary weights at the leading order in the large central charge expansion.

hep-th↗

arXiv2024

Six-Point AdS Gluon Amplitudes from Flat Space and Factorization

We present a powerful new approach to compute tree-level higher-point holographic correlators. Our method only exploits the flat-space limit, where we point out a novel and important simplification, and factorization of amplitudes in AdS. In particular, it makes minimal use of supersymmetry, crucial in all previous bootstrap methods. We demonstrate our method by computing the six-point super gluon amplitude of super Yang-Mills in AdS$_5$.

hep-th↗

arXiv2023

Defect two-point functions in 6d (2,0) theories

We consider correlation functions in 6d $(2,0)$ theories of two $\frac{1}{2}$-BPS operators inserted away from a $\frac{1}{2}$-BPS surface defect. In the large central charge limit the leading connected contribution corresponds to sums of tree-level Witten diagram in AdS$_7\times$S$^4$ in the presence of an AdS$_3$ defect. We show that these correlators can be uniquely determined by imposing only superconformal symmetry and consistency conditions, eschewing the details of the complicated effective Lagrangian. We explicitly compute all such two-point functions. The result exhibits remarkable hidden simplicity.

hep-th↗

arXiv2023

Aspects of higher-point functions in BCFT$_d$

We study three-point correlation functions of scalar operators in conformal field theories with boundaries and interfaces. We focus on two cases where there are one bulk and two boundary operators (B$\partial\partial$), or two bulk and one boundary operators (BB$\partial$). We perform a detailed analysis of the conformal blocks in different OPE channels. In particular, we obtain the bulk channel conformal blocks of the BB$\partial$ three-point functions for arbitrary exchanged spins in a series expansion with respect to the radial coordinates. We also study examples of such three-point functions in the simplest holographic dual where the $AdS_{d+1}$ space contains a brane filling an $AdS_d$ subspace. Such a setup arises in top-down models with probe branes and is also relevant for the functional approach to boundary and interface CFT correlators. We systematically study the Witten diagrams in this setup both in position space and in Mellin space. We also discuss in detail how to decompose these Witten diagrams into conformal blocks.

hep-th↗

arXiv2023

Simplicity of AdS Super Yang-Mills at One Loop

We perform a systematic bootstrap analysis of four-point one-loop Mellin amplitudes for super gluons in $\mathrm{AdS}_5\times\mathrm{S}^3$ with arbitrary Kaluza-Klein weights. The analysis produces the general expressions for these amplitudes at extremalities two and three, as well as analytic results for many other special cases. From these results we observe remarkable simplicity. We find that the Mellin amplitudes always contain only simultaneous poles in two Mellin-Mandelstam variables, extending a previous observation in the simplest case with the lowest Kaluza-Klein weights. Moreover, we discover a substantial extension of the implication of the eight-dimensional hidden conformal symmetry, which goes far beyond the Mellin poles associated with the leading logarithmic singularities. This leaves only a small finite set of poles which can be determined on a case-by-case basis from the contributions of protected operators in the OPE.

hep-th↗

arXiv2023

AdS super gluon scattering up to two loops: A position space approach

We carry out a bootstrap study of four-point correlators in 4d $\mathcal{N}=2$ SCFTs which are dual to super Yang-Mills on $AdS_5\times S^3$. We focus on the simplest $\frac{1}{2}$-BPS operators which correspond to the super gluons in the massless current multiplet. Our computation is based on an ansatz in position space which is inspired by a hidden symmetry structure manifest in the leading terms of the Lorentzian singularities of the correlators. By using other consistency conditions, we completely fix the super gluon correlators at one and two loops in the bulk genus expansion, up to possible counterterms. Our results reveal a number of interesting properties enriched by the color structures. In particular, the implication of hidden conformal symmetry on the full super gluon reduced correlator exhibits an analogous pattern as in the $AdS_5\times S^5$ supergravity correlators recently computed up to two loops.

hep-th↗