arXiv subjects

Chanyong Park

Publications and source records attributed to Chanyong Park.

At least 19 recordsLinked to original sources

arXiv2026

Lower-dimensional behavior from factorized infrared geometries along holographic RG flows

We study the emergence of effective lower-dimensional behavior in heavy-scalar two-point functions along holographic RG flows. For charged asymptotically AdS black holes, the equal-time spatial correlator remains exponentially screened, while the temporal correlator exhibits distinct temperature-dependent regimes. Away from extremality, the controlled late-time sector is the Schwarzschild-connected saddle, whose decay rate requires matching to the full geometry. Near extremality, an AdS$_2$ throat supports an additional sector whose leading decay rate is fixed by the throat data. For RN-AdS$_4$, sufficiently near extremality, this throat contribution dominates at asymptotically late times if its matched amplitude is nonzero. At extremality, the thermal throat exponential is replaced by the AdS$_2$ power law. We also study the complete zero-density magnetic-brane flow from AdS$_5$ to AdS$_3\times \mathbb{R}^2$. The transverse heavy-scalar correlator remains exponentially screened, whereas the longitudinal correlator approaches the AdS$_3$/CFT$_2$ power law in the infrared. These results show that factorized infrared geometries can support effective lower-dimensional conformal dynamics whose realization depends on temperature, direction, and the relevant saddle sector, without implying dimensional reduction of the microscopic QFT.

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arXiv2026

Heavy holographic correlators in defect conformal field theories

We study holographic defect conformal field theories which are dual to probe branes with bottom-up methods. First we determine the embedding of codimension-1 interface branes in AdS space. Then we compute defect one and two-point functions of heavy scalar operators at strong coupling. We use geodesic approximations to compute reflected two-point functions in two ways, as well as ambient and defect-channel two-point functions. In appropriate limits, our results agree with the operator product expansion (OPE) and the boundary operator expansion (BOE).

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arXiv2026

Dual gravities from entanglement entropy

Applying a rule-based holographic method, we investigate the reconstruction of dual gravity theories from the quantum field theory (QFT) data, specifically entanglement entropy. We first derive a three-dimensional black hole geometry from the entanglement entropy of a two-dimensional thermal system. Using the reconstructed solution, we extract various thermodynamic quantities with small numerical errors. Moreover, we explore how to reconstruct the dual gravity theory beyond the geometry itself. For an undeformed conformal field theory (CFT), we show that the dual gravity theory can be constructed analytically from the analytic form of the entanglement entropy. In particular, we demonstrate how to reconstruct the analytic dual geometry by applying the Abel transformation. Finally, we investigate the numerical reconstruction of the dual gravity theory from numerical entanglement entropy data for a relevantly deformed CFT. After reconstructing the dual gravity, we show that additional information about the renormalization group (RG) flow, for instance, the $\b$-function and the $c$-function, can be extracted for the considered relevantly deformed CFT.

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arXiv2026

A.X K1 Technical Report

We introduce A.X K1, a 519B-parameter Mixture-of-Experts (MoE) language model trained from scratch. Our design leverages scaling laws to optimize training configurations and vocabulary size under fixed computational budgets. A.X K1 is pre-trained on a corpus of approximately 10T tokens, curated by a multi-stage data processing pipeline. Designed to bridge the gap between reasoning capability and inference efficiency, A.X K1 supports explicitly controllable reasoning to facilitate scalable deployment across diverse real-world scenarios. We propose a simple yet effective Think-Fusion training recipe, enabling user-controlled switching between thinking and non-thinking modes within a single unified model. Extensive evaluations demonstrate that A.X K1 achieves performance competitive with leading open-source models, while establishing a distinctive advantage in Korean-language benchmarks.

cs.CL↗

arXiv2025

Holography Transformer

We have constructed a generative artificial intelligence model to predict dual gravity solutions when provided with the input of holographic entanglement entropy. The model utilized in our study is based on the transformer algorithm, widely used for various natural language tasks including text generation, summarization, and translation. This algorithm possesses the ability to understand the meanings of input and output sequences by utilizing multi-head attention layers. In the training procedure, we generated pairs of examples consisting of holographic entanglement entropy data and their corresponding metric solutions. Once the model has completed the training process, it demonstrates the ability to generate predictions regarding a dual geometry that corresponds to the given holographic entanglement entropy. Subsequently, we proceed to validate the dual geometry to confirm its correspondence with the holographic entanglement entropy data.

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arXiv2025

Correlation functions in expanding universes

By using the braneworld model, we investigate the time evolution of microscopic and macroscopic correlations in expanding universes. To describe the FLRW cosmologies in the holographic setup, we take into account a braneworld moving in the $p$-brane gas geometry, where the radial motion of the braneworld determines the cosmology in the braneworld. We show that the braneworld model reproduces the standard cosmology exactly. In this braneworld model, we investigate the time-dependent mutual information between two disjoint macroscopic subregions and the time-dependent two-point functions in the expanding universes. We find that the mutual information becomes zero when the distance between two subregions is slightly larger than the subsystem size. We also find that it decreases as time and the density of matter increase. On the other hand, the microscopic two-point function in the short-distance limit decreases by a power law, while it is exponentially suppressed in the long-distance limit due to the screening effect. In addition, we find that the two-point function is also suppressed by a power law with time.

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arXiv2024

IR physics from the holographic RG flow

We use the holographic method to investigate an RG flow and IR physics of a two-dimensional conformal field theory (CFT) deformed by a relevant scalar operator. On the dual gravity side, a renormalization group (RG) flow from a UV to IR CFT can be described by rolling a scalar field from an unstable to a stable equilibrium point. After considering a simple scalar potential allowing several local equilibrium points, we study the change of a coupling constant and ground state from the momentum-space and real-space RG flow viewpoints. For the real-space RG flow, we calculate the entanglement entropy as a function of a coupling constant and then explicitly show that the entanglement entropy diverges logarithmically at fixed points due to the restoration of conformal symmetry. We further study how the change of a ground state affects the two-point function and conformal dimension of a local operator numerically and analytically in the probe limit.

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arXiv2024

Correlation functions of boundary and defect conformal field theories

Applying the holographic method, we investigate correlation functions of boundary and defect conformal field theories. To describe boundary conformal field theory, we consider an end of the world brane in an asymptotic AdS space which behaves as a boundary in the dual conformal field theory. In this holographic setup, we calculate correlation functions involving the reflection effect at the boundary. We show that, when the end of the world brane has no degrees of freedom, the holographic calculation reproduces the correlation functions known in the boundary conformal field theory. When the boundary has nontrivial boundary entropy, we calculate one- and two-point functions nontrivially relying on the boundary entropy. We further study correlation functions of defect conformal field theory after introducing a $p$-brane. We directly derive a bulk-to-defect two-point function without introducing an image operator and determine the coefficient of the two-point function exactly in the holographic setup.

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arXiv2023

End of the World Perspective to BCFT

In this work, we study the end-of-the-world (EOW) branes anchored to the boundaries of BCFT${}_2$ dual to the BTZ black hole. First, we explore the thermodynamics of the boundary system consisting of the conformal boundary and two EOW branes. This thermodynamics is extended by the tension appearing as the effective cosmological constant of JT black holes on the EOW branes. The tension contribution is identified with the shadow entropy equivalent to the boundary entropy of the BCFT${}_2$. The thermodynamics of the JT black holes and the bulk of BCFT${}_2$ can be combined into a novel grafted thermodynamics based on the first law. Second, we focus on the observer's view of the EOW branes by lowering the temperature. We show that the EOW branes generate a scale called ``reefs" inside the horizon. This scale also appears in the grafted thermodynamics. At high temperatures, observers on the EOW branes see their respective event horizons. The reef starts to grow relatively to the horizon size at the temperature, $T_{grow}$. As the temperature cools down the reef area fills the entire interior of the JT black holes at the temperature $T_{out}$. Then, the observers recognize their horizons disappear and see the large density of the energy flux. At this temperature, the two JT regions become causally connected. This connected spacetime has two asymptotic $AdS_2$ boundaries with a conformal matter. Also, we comment on the grafted thermodynamics to higher dimensions in Appendix B.

hep-th↗

arXiv2023

Holographic description for correlation functions

We study general correlation functions of various quantum field theories in the holographic setup. Following the holographic proposal, we investigate correlation functions via a geodesic length connecting boundary operators. We show that this holographic description can reproduce the known two- and three-point functions of conformal field theory. Using this holographic method, we further study general two-point functions of a two-dimensional thermal CFT and of a scalar field theory living in a dS or AdS space. Due to the nontrivial thermal or curvature effect, the two-point functions in an IR limit show different scaling behaviors from those of the UV CFT. We study such nontrivial IR scaling behaviors by applying the holographic method.

hep-th↗

arXiv2023

Holographic RG flow triggered by gluon condensate

By applying the holographic method, we study a non-perturbative renormalization group (RG) flow triggered by a gluon condensate. After introducing a bulk scalar field in an AdS space related to the gluon condensate, we investigate the trace anomaly proportional to the gluon condensate. The holographic calculation reproduces the one-loop trace anomaly known in the lattice QCD. We also show that higher loop corrections give rise to additional contributions and modify the one-loop trace anomaly.

hep-th↗

arXiv2023

Holographic two-point functions in a disorder system

We study the holographic dual of two-point correlation functions for nonconformal field theories. We first take into account a Lifshitz geometry as the dual of a Lifshitz field theory which may appear at a critical or IR fixed point. We explicitly show the holographic relation between a Lifshitz geometry and a Lifshitz field theory by calculating two-point correlators and equation of state parameter on both sides. We also investigate a disorder deformation, which allows a UV conformal field theory to flow into a new IR Lifshitz field theory. In this deformed theory, we investigate an anomalous dimension representing the change of an operator's scaling dimension along the RG flow.

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arXiv2023

Holographic entanglement entropy probe on spontaneous symmetry breaking with vector order

We study holographic entanglement entropy in 5-dimensional charged black brane geometry obtained from Einstein-SU(2)Yang-Mills theory defined in asymptotically AdS space. This gravity system undergoes second order phase transition near its critical point affected by a spatial component of the Yang-Mills fields, which is normalizable mode of the solution. This is known as phase transition between isotropic and anisotropic phases. We get analytic solutions of holographic entanglement entropies by utilizing the solution of bulk spacetime geometry given in arXiv:1109.4592, where we consider subsystems defined on AdS boundary of which shapes are wide and thin slabs and a cylinder. It turns out that the entanglement entropies near the critical point shows scaling behavior such that for both of the slabs and cylinder, $Δ_\varepsilon S\sim\left(1-\frac{T}{T_c}\right)^β$ and the critical exponent $β=1$, where $Δ_\varepsilon S\equiv S^{iso}-S^{aniso}$, and $S^{iso}$ denotes the entanglement entropy in isotropic phase whereas $S^{aniso}$ denotes that in anisotropic phase. We suggest a quantity $O_{12}\equiv S_1-S_2$ as a new order parameter near the critical point, where $S_1$ is entanglement entropy when the slab is perpendicular to the direction of the vector order whereas $S_2$ is that when the slab is parallel to the vector order. $O_{12}=0$ in isotropic phase but in anisotropic phase, the order parameter becomes non-zero showing the same scaling behavior. Finally, we show that even near the critical point, the first law of entanglement entropy is hold. Especially, we find that the entanglement temperature for the cylinder is $\mathcal T_{cy}=\frac{c_{ent}}{a}$, where $c_{ent}=0.163004\pm0.000001$ and $a$ is the radius of the cylinder.

hep-th↗

arXiv2022

Holographic two-point functions in medium

We study two-point correlation function in a medium composed of two kinds of matter, which is the dual of a three-dimensional generalized $p$-brane gas geometry. Following the holographic prescription, we calculate temporal and spatial two-point functions in the medium. In general, the screening effect of the medium makes two-point functions decrease more rapidly than the CFT's two-point function. In the extremal limit, however, we find that a temporal two-point function is still conformal. This indicates that a two-dimensional UV CFT flows into a one-dimensional quantum mechanics in the IR limit. This is consistent with the fact that the near horizon geometry in the extremal limit reduces to AdS$_2$. We also investigate holographic mutual information representing the correlation between two subsystems. We show that a critical distance in the IR region, where the mutual information vanishes, leads to a similar behavior to the correlation length of a two-point function.

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arXiv2022

Dual Geometry of Entanglement Entropy via Deep Learning

For a given entanglement entropy of QFT, we investigate how to reconstruct its dual geometry by applying the Ryu-Takayanagi formula and the deep learning method. In the holographic setup, the radial direction of the dual geometry is identified with the energy scale of the dual QFT. Therefore, the holographic dual geometry can describe how the QFT changes along the RG flow. Intriguingly, we show that the reconstructed geometry only from the entanglement entropy data can give us more information about other physical properties like thermodynamic quantities in the IR region.

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arXiv2022

Quantum correlation in quark-gluon medium

We study thermodynamics and quantum correlations of the string cloud geometry whose field theory dual is the quark-gluon medium. We found the novel universality of the entanglement entropy first law in the high quark density limit. We also showed that a correlation function generally decreases as the entanglement entropy of the background medium increases due to the screening effect of the background. We study the UV and IR effects of the medium on phase transition behaviour observed in the holographic mutual information using both perturbative and numerical computations. Moreover, by numerical computation, we show that in the IR region the critical length obtained from the mutual information behaves similar to the correlation length of the two-point function.

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arXiv2022

Holographic time-dependent entanglement entropy in $p$-brane gas geometries

We study the time evolution of entanglement entropy in expanding universes with various matters. To describe expanding universes holographically, we take into account a braneworld moving in an asymptotic AdS space involving a uniform $p$-brane gas. In the braneworld model, an observer living in the braneworld detects the bulk motion of the braneworld as an expanding universe. We show that the entanglement entropy of expanding universes increases by the volume law in the early time and by the area law in the late time. We further consider the cosmological horizon, which is the border of the visible and invisible universe, and then investigate the time-dependent quantum entanglement between them across the cosmological horizon.

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arXiv2021

Time-dependent quantum correlations in two-dimensional expanding spacetime

In expanding universes, the entanglement entropy must be time-dependent because the background geometry changes with time. For understanding time evolution of quantum correlations, we take into account two distinct holographic models, the dS boundary model and the braneworld model. In this work, we focus on two-dimensional expanding universes for analytic calculation and comparison. Although two holographic models realize expanding universes in totally different ways, we show that they result in the qualitatively same time-dependence for eternal inflation. We further investigate the time-dependent correlations in the radiation-dominated era of the braneworld model. Intriguingly, the holographic result reveals that a thermal system in the expanding universe is {\it dethermalized} after a critical time characterized by the subsystem size.

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