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Masaki Murata

Publications and source records attributed to Masaki Murata.

At least 19 recordsLinked to original sources
arXiv2025

Gluon scattering amplitudes with instantons and minimal surfaces with topology change

We study the instanton effect on the gluon scattering amplitudes at strong coupling and large $N$ for the ${\cal N}=4$ supersymmetric Yang-Mills theory. According to Alday and Maldacena, the gluon scattering amplitude corresponds holographically to the area of a worldsheet minimal surface in the T-dual AdS${}_5$ geometry. The Yang-Mills instanton introduces an instanton D-brane in the geometry, with which a particular boundary condition for the minimal surface is imposed. We show that the minimal surface undergoes a topology change depending on the size and the gluon momenta, and that the instanton amplitude exhibits a characteristic dependence on gluon momenta. More specifically, we find that when the fixed instanton size modulus $ρ$ is larger than ${\cal O}(\sqrtλ/E)$ where $λ$ is the 't Hooft coupling and $E$ is the typical momentum of the scattering gluon, due to the topology change of the worldsheet minimal surface, the instanton amplitude is exponentially enhanced as $\exp(ρE)$.

hep-th↗
arXiv2025

Physics-informed neural network solves minimal surfaces in curved spacetime

We develop a flexible framework based on physics-informed neural networks (PINNs) for solving boundary value problems involving minimal surfaces in curved spacetimes, with a particular emphasis on singularities and moving boundaries. By encoding the underlying physical laws into the loss function and designing network architectures that incorporate the singular behavior and dynamic boundaries, our approach enables robust and accurate solutions to both ordinary and partial differential equations with complex boundary conditions. We demonstrate the versatility of this framework through applications to minimal surface problems in anti-de Sitter (AdS) spacetime, including examples relevant to the AdS/CFT correspondence (e.g. Wilson loops and gluon scattering amplitudes) popularly used in the context of string theory in theoretical physics. Our methods efficiently handle singularities at boundaries, and also support both "soft" (loss-based) and "hard" (formulation-based) imposition of boundary conditions, including cases where the position of a boundary is promoted to a trainable parameter. The techniques developed here are not limited to high-energy theoretical physics but are broadly applicable to boundary value problems encountered in mathematics, engineering, and the natural sciences, wherever singularities and moving boundaries play a critical role.

hep-th↗
arXiv2024

Machine-learning emergent spacetime from linear response in future tabletop quantum gravity experiments

We introduce a novel interpretable Neural Network (NN) model designed to perform precision bulk reconstruction under the AdS/CFT correspondence. According to the correspondence, a specific condensed matter system on a ring is holographically equivalent to a gravitational system on a bulk disk, through which tabletop quantum gravity experiments may be possible as reported in arXiv:2211.13863. The purpose of this paper is to reconstruct a higher-dimensional gravity metric from the condensed matter system data via machine learning using the NN. Our machine reads spatially and temporarily inhomogeneous linear response data of the condensed matter system, and incorporates a novel layer that implements the Runge-Kutta method to achieve better numerical control. We confirm that our machine can let a higher-dimensional gravity metric be automatically emergent as its interpretable weights, using a linear response of the condensed matter system as data, through supervised machine learning. The developed method could serve as a foundation for generic bulk reconstruction, i.e., a practical solution to the AdS/CFT correspondence, and would be implemented in future tabletop quantum gravity experiments.

hep-th↗
arXiv2024

Comparative Study of Neural Network Methods for Solving Topological Solitons

Topological solitons, which are stable, localized solutions of nonlinear differential equations, are crucial in various fields of physics and mathematics, including particle physics and cosmology. However, solving these solitons presents significant challenges due to the complexity of the underlying equations and the computational resources required for accurate solutions. To address this, we have developed a novel method using neural network (NN) to efficiently solve solitons. A similar NN approach is Physics-Informed Neural Networks (PINN). In a comparative analysis between our method and PINN, we find that our method achieves shorter computation times while maintaining the same level of accuracy. This advancement in computational efficiency not only overcomes current limitations but also opens new avenues for studying topological solitons and their dynamical behavior.

hep-th↗
arXiv2015

Transport Process in Multi-Junctions of Quantum Systems

We consider the junction of multiple one-dimensional systems and study how conserved currents transport at the junction. To characterize the transport process, we introduce reflection/transmission coefficients by applying boundary conformal field theory. We compute the reflection/transmission coefficients for some examples to derive the closed formulas. The formulas demonstrate spin-flip transport, where the spin polarization is flipped at the junction.

hep-th↗
arXiv2014

Current Reflection and Transmission at Conformal Defects: Applying BCFT to Transport Process

We study reflection/transmission process at conformal defects by introducing new transport coefficients for conserved currents. These coefficients are defined by using BCFT techniques thanks to the folding trick, which turns the conformal defect into the boundary. With this definition, exact computations are demonstrated to describe reflection/transmission process for a class of conformal defects. We also compute the boundary entropy based on the boundary state.

hep-th↗
arXiv2013

Multibrane Solutions in Open String Field Theory

We study properties of a class of solutions of open string field theory which depend on a single holomorphic function F(z). We show that the energy of these solutions is well defined and is given by integer multiples of a single D-brane tension. Potential anomalies are discussed in detail. Some of them can be avoided by imposing suitable regularity conditions on F(z), while the anomaly in the equation of motion seems to require an introduction of the so called phantom term.

hep-th↗
arXiv2012

A Landscape in Boundary String Field Theory: New Class of Solutions with Massive State Condensation

We solve the equation of motion of boundary string field theory allowing generic boundary operators quadratic in $X$, and explore string theory non-perturbative vacua with massive state condensation. Using numerical analysis, a large number of new solutions are found. Their energies turn out to distribute densely in the range between the D-brane tension and the energy of the tachyon vacuum. We discuss an interpretation of these solutions as perturbative closed string states. From the cosmological point of view, the distribution of the energies can be regarded as the so-called landscape of string theory, as we have a vast number of non-perturbative string theory solutions including one with small vacuum energy.

hep-th↗
arXiv2012

No-Ghost Theorem for Neveu-Schwarz String in 0-Picture

The no-ghost theorem for Neveu-Schwarz string is directly proved in 0-picture. The one-to-one correspondence between physical states in 0-picture and those in the conventional (-1)-picture are confirmed. It is shown that a non-trivial metric consistent with the BRST cohomology is needed to define a positive semi-definite norm in the physical Hilbert space. As a by-product, we find a new inverse picture changing operator, which is non-covariant but has non-singular operator product with itself. A possibility to construct a new gauge invariant superstring field theory is discussed.

hep-th↗
arXiv2011

On Multibrane Solutions in Open String Field Theory

Existence of open string field theory solutions describing configurations of multiple space-filling D-branes has been a subject of numerous speculations for quite some time. In this talk we present some new results giving further support to these ideas.

hep-th↗
arXiv2010

E6,7,8 Magnetized Extra Dimensional Models

We study 10D super Yang-Mills theory with the gauge groups $E_6$, $E_7$ and $E_8$. We consider the torus/orbifold compacfitication with magnetic fluxes and Wilson lines. They lead to 4D interesting models with three families of quarks and leptons, whose profiles in extra dimensions are quasi-localized because of magnetic fluxes.

hep-ph↗
arXiv2009

Melting Spectral Functions of the Scalar and Vector Mesons in a Holographic QCD Model

We investigate the finite-temperature spectral functions of heavy quarkonia by using the soft-wall AdS/QCD model. We discuss the scalar, the pseudo-scalar, the vector, and the axial-vector mesons and compare their qualitative features of the melting temperature and growing width. We find that the axial-vector meson melts earlier than the vector meson, while there appears only a slight difference between the scalar and pseudo-scalar mesons which also melt earlier than the vector meson.

hep-ph↗
arXiv2009

Finite-temperature spectral function of the vector mesons in an AdS/QCD model

We use the soft-wall AdS/QCD model to investigate the finite-temperature effects on the spectral function in the vector channel. The dissociation of the vector meson tower onto the AdS black hole leads to the in-medium mass shift and the width broadening in a way similar to the lattice QCD results for the heavy quarkonium at finite temperature. We also show the momentum dependence of the spectral function and find it consistent with screening in a hot wind.

hep-ph↗
arXiv2008

Chiral currents and static properties of nucleons in holographic QCD

We analyze static properties of nucleons in the two flavor holographic QCD model of Sakai and Sugimoto described effectively by a five-dimensional U(2) Yang-Mills theory with the Chern-Simons term on a curved background. The baryons are represented in this model as a soliton, which at a time slice is approximately the BPST instanton with a fixed size. First, we construct a chiral current in four dimensions from the Noether current of local gauge transformations which are non-vanishing on the boundaries of the extra dimension. We examine this chiral current for nucleons with quantized collective coordinates to compute their charge distribution, charge radii, magnetic moments and axial vector coupling. Most of the results are better close to the experimental values than in the Skyrme model. We discuss the problems of our chiral current; non-uniqueness of the local gauge transformation for defining the current, and its gauge-noninvariance.

hep-th↗
arXiv2007

Baryons and the Chern-Simons term in holographic QCD with three flavors

We study dynamical baryons in the holographic QCD model of Sakai and Sugimoto in the case of three flavors and with special interest in the construction of the Chern-Simons (CS) term. The baryon classical solution in this model is given by the BPST instanton, and we carry out the collective coordinate quantization of the solution. The CS term should give rise to a first class constraint which selects baryon states with right spins. However, the original CS term written in terms of the CS 5-form does not work. We instead propose a new CS term which is gauge invariant and is given as an integral over a six dimensional space having as its boundary the original five dimensional spacetime of the holographic model. Collective coordinate quantization using our new CS term leads to correct baryon states and their mass formula.

hep-th↗
arXiv2002

Using the DIFF Command for Natural Language Processing

Diff is a software program that detects differences between two data sets and is useful in natural language processing. This paper shows several examples of the application of diff. They include the detection of differences between two different datasets, extraction of rewriting rules, merging of two different datasets, and the optimal matching of two different data sets. Since diff comes with any standard UNIX system, it is readily available and very easy to use. Our studies showed that diff is a practical tool for research into natural language processing.

cs.CL↗