arXiv subjects

Shoichi Kawamoto

Publications and source records attributed to Shoichi Kawamoto.

At least 19 recordsLinked to original sources

arXiv2026

Fermionic modes of D-instanton wormholes from broken local supersymmetry

In low-energy supergravity treatment of type IIB superstring on general D-instanton wormhole profiles in the bulk, we obtain non-vanishing scalar two-point functions in addition to the vanishing $\langle τ^* τ^* \rangle$ that corresponds to the BPS amplitude detected by two D-instantons at their respective boundaries. This is exploited to show that the modes of broken local supersymmetry in the bulk deliver the fermionic (diagonal) modes on the boundaries through the deformation by the form of current-current two point functions propagating on the tree level cylinder geometry. Our treatment is generalizable to multi D-instanton cases and general Euclidean branes.

hep-th↗

arXiv2026

Out-of-Time-Order-Correlators in Holographic EPR pairs

In this note, we investigate the out-of-time-order correlators (OTOCs) for quantum fields in a holographic framework describing Einstein-Podolsky-Rosen (EPR) pairs. We compute the four-point and six-point OTOCs using the gravity dual, represented by the string worldsheet theory in Anti-de Sitter (AdS) space. These correlators quantify the rate at which information is scrambled, leading to the disentanglement of the EPR pair. We demonstrate consistency between two approaches for calculating OTOCs: the holographic influence functional on worldsheets perturbed by shock waves, and the worldsheet scattering in the eikonal approximation. We show that the OTOCs exhibit an initial phase of exponential growth, with six-point correlators indicating a marginally longer scrambling time compared to four-point correlators.

hep-th↗

arXiv2026

Decoherence by black holes via holography

In this note, we reexamine decoherence effects in quantum field theories with gravity duals. The thought experiment proposed in \cite{DSW_22, DSW_23}, which reveals novel decoherence patterns associated with black holes, also manifests itself from the perspective of the boundary theory. In particular, we consider a moving mirror coupled to quantum critical theories characterized by a dynamical exponent $z$ that are dual to asymptotically Lifshitz geometries. The interference experiment occurs on the boundary, where a superposition of two spatially separated quantum states of a mirror is maintained for a finite time $τ_0$ before recombination. We find that the interaction with a quantum field at finite temperature, arising from the presence of a Lifshitz black hole, leads to a constant decoherence rate. In contrast, for the zero-temperature case corresponding to pure Lifshitz spacetime, the decoherence rate vanishes in the large-time limit $τ_0 \to \infty$. Remarkably, in the zero-temperature regime, the decoherence exhibits a power-law decay at large $τ_0$ as $z \rightarrow \infty$, a behavior reminiscent of the decoherence patterns seen in extremal black hole geometries. In addition, we investigate the decoherence of one particle in an EPR pair constructed holographically. Our results indicate that causality plays a crucial role in determining whether the entanglement leads to the suppression of decoherence in the other particle.

hep-th↗

arXiv2022

Time dependent field correlators from holographic EPR pairs

We study the correlators of the fields that couple to the quark and anti-quark EPR pair in the super Yang-Mills theory using the holographic description, which is a string in AdS space with its two ends anchoring on the boundaries. We consider the cases that the endpoints of the string are static and that the endpoints are uniformly accelerated in opposite directions where the exact solutions for the string's profiles are available. In both cases, the two-point correlators of the boundary field, described by the linearized perturbations in the worldsheet, can also be derived exactly where we obtain the all-time evolution of the correlators. In the case of the accelerating string, the induced geometry on the string worldsheet has the causal structure of a two-sided AdS black hole with a wormhole connecting two causally disconnected boundaries, which can be a realization of the ER=EPR conjecture. We find that causality plays a crucial role in determining the nature of the dispersion relation of the particle and the feature of the induced mutual interaction between two particles from the field. In the case that two boundaries of the worldsheet are causally disconnected, the induced effect from the field gives the dissipative dynamics of each particle with no dependence on the distance between two particles, and the induced mutual coupling between them vanishes in the late times, following a power law. When two ends are causally connected, the induced dispersion relation becomes non-dissipative in the late times. Here, we will also comment on the implications of our findings to the entangled particle dynamics and the ER=EPR conjecture.

hep-th↗

arXiv2021

Momentum-space entanglement in scalar field theory on fuzzy spheres

Quantum field theory defined on a noncommutative space is a useful toy model of quantum gravity and is known to have several intriguing properties, such as nonlocality and UV/IR mixing. They suggest novel types of correlation among the degrees of freedom of different energy scales. In this paper, we investigate such correlations by the use of entanglement entropy in the momentum space. We explicitly evaluate the entanglement entropy of scalar field theory on a fuzzy sphere and find that it exhibits different behaviors from that on the usual continuous sphere. We argue that these differences would originate in different characteristics; non-planar contributions and matrix regularization. It is also found that the mutual information between the low and the high momentum modes shows different scaling behaviors when the effect of a cutoff becomes important.

hep-th↗

arXiv2019

Spin chains and classical strings in two parameters $q$-deformed AdS$_3\times$S$^3$

In this paper, we study the spin chain and string excitation in the two-parameters $q$-deformed AdS$_3\times$S$^3$ proposed by Hoare. We obtain the deformed spin chain model at the fast spin limit for choices of deformed parameters. General ansatz for giant magnons are studied in great detail and complicated dispersion relation is treated perturbatively. We also study several types of hanging string solutions and their charges and spins are analyzed numerically. At last, we explore its pp-wave limit and find its solution only depends on the difference of deformed parameters.

hep-th↗

arXiv2018

Charged rotating BTZ black holes in noncommutative spaces and torsion gravity

We consider charged rotating BTZ black holes in noncommutative space by use of Chern-Simons theory formulation of $2+1$ dimensional gravity. The noncommutativity between the radial and the angular variables is introduced through the Seiberg-Witten map for gauge fields, and the deformed geometry to the first order in the noncommutative parameter is derived. It is found that the deformation also induces nontrivial torsion, and the Einstein-Cartan theory appears to be a suitable framework to investigate the equations of motion. Though the deformation is indeed nontrivial, the deformed and the original Einstein equations are found to be related by a rather simple coordinate transformation.

hep-th↗

arXiv2017

Entropic uncertainty relation based on generalized uncertainty principle

We explore the modification of the entropic formulation of uncertainty principle in quantum mechanics which measures the incompatibility of measurements in terms of Shannon entropy. The deformation in question is the type so called generalized uncertainty principle that is motivated by thought experiments in quantum gravity and string theory and is characterized by a parameter of Planck scale. The corrections are evaluated for small deformation parameters by use of the Gaussian wave function and numerical calculation. As the generalized uncertainty principle has proven to be useful in the study of the quantum nature of black holes, this study would be a step toward introducing an information theory viewpoint to black hole physics.

hep-th↗

arXiv2017

Extremal noncommutative black holes as dark matter furnaces

In this letter, we consider dark matter annihilation in the gravitational field of noncommutative black holes. At final stage of evaporation, we hypothesize the existence of a thermal equilibrium state composed of a burning black hole relics fueled by dark matter accretion.

hep-th↗

arXiv2015

Size scaling of self gravitating polymers and strings

We study a statistical ensemble of a single polymer with self gravitational interaction. This is a model of a gravitating string --- the precursor of a black hole. We analyze averaged sizes by mean field approximations with an effective Hamiltonian a la Edwards with Newtonian potential as well as a contact repulsive interaction. We find that there exists a certain scaling region where the attractive and the repulsive forces balance out. The repulsive interaction pushes the critical gravitational coupling to a larger value, at which the size of a polymer becomes comparable to its Schwarzschild radius, and as a result the size of the corresponding black hole increases considerably. We show phase diagrams in various dimensions that clarify how the size changes as the strengths of repulsive and gravitational forces vary.

hep-th↗

arXiv2015

Existence of new nonlocal field theory on noncommutative space and spiral flow in renormalization group analysis of matrix models

In the previous study, we formulate a matrix model renormalization group based on the fuzzy spherical harmonics with which a notion of high/low energy can be attributed to matrix elements, and show that it exhibits locality and various similarity to the usual Wilsonian renormalization group of quantum field theory. In this work, we continue the renormalization group analysis of a matrix model with emphasis on nonlocal interactions where the fields on antipodal points are coupled. They are indeed generated in the renormalization group procedure and are tightly related to the noncommutative nature of the geometry. We aim at formulating renormalization group equations including such nonlocal interactions and finding existence of nontrivial field theory with antipodal interactions on the fuzzy sphere. We find several nontrivial fixed points and calculate the scaling dimensions associated with them. We also consider the noncommutative plane limit and then no consistent fixed point is found. This contrast between the fuzzy sphere limit and the noncommutative plane limit would be manifestation in our formalism of the claim given by Chu, Madore and Steinacker that the former does not have UV/IR mixing, while the latter does.

hep-th↗

arXiv2014

To see Symmetry in a Forest of Trees

The exact symmetry identities among four-point tree-level amplitudes of bosonic open string theory as derived by G. W. Moore are re-examined. The main focuses of this work are: (1) Explicit construction of kinematic configurations and a new polarization basis for the scattering processes. These setups simplify greatly the functional forms of the exact symmetry identities, and help us to extract easily high-energy limits of stringy amplitudes appearing in the exact identities. (2) Connection and comparison between D. J. Gross's high-energy stringy symmetry and the exact symmetry identities as derived by G. W. Moore. (3) Observation of symmetry patterns of stringy amplitudes with respect to the order of energy dependence in scattering amplitudes.

hep-th↗

arXiv2013

A Renormalization Group Approach to A Yang-Mills Two Matrix Model

A Yang-Mills type two matrix model with mass terms is studied by use of a matrix renormalization group approach proposed by Brezin and Zinn-Justin. The renormalization group method indicates that the model exhibits a critical behavior similar to that of two dimensional Euclidean gravity. A massless limit and the generation of quadratic terms along the renormalization group flow are discussed.

hep-th↗

arXiv2013

Emission spectrum of soft massless states from heavy superstring

We calculate emission rates of various bosonic/fermionic soft massless states of open/closed superstring from an ensemble of a highly excited open/closed superstring in the flat background. The resulting spectrum shows thermal distributions at the Hagedorn temperature. We find greybody factors for each process and observe their relation to the ones from blackholes.

hep-th↗

arXiv2012

Renormalization group approach to matrix models via noncommutative space

We develop a new renormalization group approach to the large-N limit of matrix models. It has been proposed that a procedure, in which a matrix model of size (N-1) \times (N-1) is obtained by integrating out one row and column of an N \times N matrix model, can be regarded as a renormalization group and that its fixed point reveals critical behavior in the large-N limit. We instead utilize the fuzzy sphere structure based on which we construct a new map (renormalization group) from N \times N matrix model to that of rank N-1. Our renormalization group has great advantage of being a nice analog of the standard renormalization group in field theory. It is naturally endowed with the concept of high/low energy, and consequently it is in a sense local and admits derivative expansions in the space of matrices. In construction we also find that our renormalization in general generates multi-trace operators, and that nonplanar diagrams yield a nonlocal operation on a matrix, whose action is to transport the matrix to the antipode on the sphere. Furthermore the noncommutativity of the fuzzy sphere is renormalized in our formalism. We then analyze our renormalization group equation, and Gaussian and nontrivial fixed points are found. We further clarify how to read off scaling dimensions from our renormalization group equation. Finally the critical exponent of the model of two-dimensional gravity based on our formalism is examined.

hep-th↗

arXiv2011

Branes from a non-Abelian (2,0) tensor multiplet with 3-algebra

In this paper, we study the equations of motion for non-Abelian N=(2,0) tensor multiplets in six dimensions, which were recently proposed by Lambert and Papageorgakis. Some equations are regarded as constraint equations. We employ a loop extension of the Lorentzian three-algebra (3-algebra) and examine the equations of motion around various solutions of the constraint equations. The resultant equations take forms that allow Lagrangian descriptions. We find various (5+d)-dimensional Lagrangians and investigate the relation between them from the viewpoint of M-theory duality.

hep-th↗

arXiv2010

Dynamical Instability of Holographic QCD at Finite Density

In this paper we study the dynamical instability of Sakai-Sugimoto's holographic QCD model at finite baryon density. In this model, the baryon density, represented by the smeared instanton on the worldvolume of the probe D8-\overline{D8} mesonic brane, sources the worldvolume electric field, and through the Chern-Simons term it will induces the instability to form a chiral helical wave. This is similar to Deryagin-Grigoriev-Rubakov instability to form the chiral density wave for large N_c QCD at finite density. Our results show that this kind of instability occurs for sufficiently high baryon number densities. The phase diagram of holographic QCD will thus be changed from the one which is based only on thermodynamics. This holographic approach provides an effective way to study the phases of QCD at finite density, where the conventional perturbative QCD and lattice simulation fail.

hep-th↗

arXiv2010

Unruh Effect and Holography

We study the Unruh effect on the dynamics of quarks and mesons in the context of AdS$_5$/CFT$_4$ correspondence. We adopt an AdS$_5$ metric with the boundary Rindler horizon extending into a bulk Rindler-like horizon, which yields the thermodynamics with Unruh temperature verified by computing the boundary stress tensor. We then embed in it a probe fundamental string and a $D7$ brane in such a way that they become the dual of an accelerated quark and a meson in Minkowski space, respectively. Using the standard procedure of holographic renormalization, we calculate the chiral condensate, and also the spectral functions for both the accelerated quark and meson. Especially, we extract the corresponding strength of random force of the Langevin dynamics and observe that it can characterize the phase transition of meson melting. This result raises an issue toward a formulation of complementarity principle for the Rindler horizon. We find most of the dynamical features are qualitatively similar to the ones in the thermal bath dual to the AdS black hole background, though they could be quite different quantitatively.

hep-th↗