arXiv subjects

Shousuke Ohmori

Publications and source records attributed to Shousuke Ohmori.

At least 19 recordsLinked to original sources

arXiv2026

Rigged Liouville space formulation for quasi-Hermitian Liouville operators

We discuss a super bra-ket formalism for quasi-Hermitian Liouvillian operators within the framework of rigged Hilbert spaces (RHS). An RHS in terms of the Liouville space, referred to as a rigged Liouville space (RLS), is reconstructed by exploiting the mathematical fact that the space of Hilbert-Schmidt operators is unitarily equivalent to the tensor product of Hilbert spaces. The obtained RLS endows a rigorous foundation of the construction for the super bra-ket and for the spectral decompositions of both Hermitian and quasi-Hermitian Liouville operators, which are characterized by the generalized eigenvectors in the dual spaces. Furthermore, within this framework, the non-Hermitian Liouvillian operator and its adjoint can be constructed symmetrically, with their symmetric structure preserved. As an application of our RLS methodology, we examine the Liouville operators corresponding to Hermitian and non-Hermitian harmonic oscillators and elucidate the differences between their spectral decomposition forms.

math-ph↗

arXiv2025

Rigged Hilbert Space Formulation of Quantum Thermo Field Dynamics and Mapping to Rigged Liouville Space

The rigged Hilbert space, a triplet extension of the Hilbert space, provides a mathematically rigorous foundation for quantum mechanics by extending the Hilbert space to accommodate generalized eigenstates. In this paper, we construct a triplet structure for the thermal space arising in Thermo Field Dynamics with the aid of the tensor product formulation of rigged Hilbert spaces, a formalism that reformulates thermal averages as pure-state expectation values in a doubled Hilbert space. We then induce the rigged Liouville space for Liouville space of density operators from the triplet structure for Thermo Field Dynamics; the rigged Liouville space corresponds isomorphically one-to-one with that of Thermo Field Dynamics. This correspondence offers a unified topological foundation for quantum statistical mechanics at finite temperature and establishes a framework for future generalizations to open and non-equilibrium quantum systems.

math-ph↗

arXiv2025

Piecewise linear cusp bifurcations in ultradiscrete dynamical systems

We investigate the dynamical properties of cusp bifurcations in max-plus dynamical systems derived from continuous differential equations through the tropical discretization and the ultradiscrete limit. A general relationship between cusp bifurcations in continuous and corresponding discrete systems is formulated as a proposition. For applications of this proposition, we analyze the Ludwig and Lewis models, elucidating the dynamical structure of their ultradiscrete cusp bifurcations obtained from the original continuous models. In the resulting ultradiscrete max-plus systems, the cusp bifurcation is characterized by piecewise linear representations, and its behavior is examined through the graph analysis.

nlin.CD↗

arXiv2024

Rigged Hilbert Space formulation for quasi-Hermitian composite systems

The discussion in this study delves into Dirac's bra-ket formalism for a quasi-Hermitian quantum composite system based on the rigged Hilbert space (RHS). We establish an RHS with a positive definite metric suitable for a quasi-Hermite composite system. The obtained RHS is utilized to construct the bra and ket vectors for the non-Hermite composite system and produce the spectral decomposition of the quasi-Hermitian operator. We show that the symmetric relations regarding quasi-Hermitian operators can be extended to dual spaces, and all descriptions obtained using the bra-ket formalism are completely developed in the dual spaces. Our methodology is applied to a non-Hermitian harmonic oscillator composed of conformal multi-dimensional many-body systems.

math-ph↗

arXiv2024

A Generalization for Ultradiscrete Limit Cycles in a Certain Type of Max-Plus Dynamical Systems

Dynamical properties of a generalized max-plus model for ultradiscrete limit cycles are investigated.This model includes both the negative feedback model and the Sel'kov model. It exhibits the Neimark-Sacker bifurcation, and possesses stable and unstable ultradiscrete limit cycles. The number of discrete states in the limit cycles can be analytically determined and its approximate relation is proposed. Additionally, relationship between the max-plus model and the two-dimensional normal form of the border collision bifurcation is discussed.

nlin.CD↗

arXiv2023

Ultradiscretization in discrete limit cycles of tropically discretized and max-plus Sel'kov models

The state of limit cycles for a tropically discretized Sel'kov model becomes ultradiscrete due to phase lock caused by a saddle-node bifurcation. This property is essentially the same as the case of the negative feedback model, and existence of a general mechanism for ultradiscretization of the limit cycles is suggested. Furthermore in the case of the max-plus Sel'kov model, we find the logarithmic dependence of the time to pass the bottleneck for phase drift motion in the vicinity of the bifurcation point. This dependency can be understood as a consequence of the piecewise linearization by applying the ultradiscrete limit.

nlin.CG↗

arXiv2023

Conway's law, revised from a mathematical viewpoint

In this article, we revise Conway's Law from a mathematical point of view. By introducing a task graph, we first rigorously state Conway's Law based on the homomorphisms in graph theory for the software system and the organizations that created it. Though Conway did not mention it, the task graph shows the geometric structure of tasks, which plays a crucial role. Furthermore, due to recent requirements for high-level treatment of communication (due to security, knowledge hiding, etc.) in organizations and hierarchical treatment of organizations, we have reformulated these statements in terms of weakened homomorphisms, and the continuous maps in graph topology. In order to use graph topology and the continuous map in Conway's law, we have prepared them as mathematical tools, and then we show the natural expression of Conway's correspondences with hierarchical structures.

cs.SE↗

arXiv2023

Construction of topological representation of geometric patterns using Cantor self-similar set

Universal representation of geometric patterns of disordered matters is investigated with the aid of general topology. By utilizing the result obtained in the previous study (S. Ohmori, et.al., Phys. Scr. 94, 105213 (2019)) that any patterns can be represented by a specific topological space, a construction of topological representation of patterns using Cantor set is shown. The obtained topological representations are then demonstrated by the contractions that characterize the self-similarity of Cantor set. For some practical geometric patterns, e.g., network, dendritic, and clusterized patterns, their topological representations are focused on.

math-ph↗

arXiv2023

Emergence of ultradiscrete states due to phase lock caused by saddle-node bifurcation in discrete limit cycles

Dynamical properties of limit cycles in a tropically discretized negative feedback model are numerically investigated. This model has a controlling parameter $\tau$, which corresponds to time interval for the time evolution of phase in the limit cycles. By considering $\tau$ as a bifurcation parameter, we find that ultradiscrete state emerges due to phase lock caused by saddle-node bifurcation. Furthermore, focusing on limit cycles for the max-plus negative feedback model, it is found that the unstable limit cycle in the max-plus model corresponds to the unstable fixed points emerging by the saddle-node bifurcation in the tropically discretized model.

nlin.AO↗

arXiv2023

Dynamical properties of discrete negative feedback models

Dynamical properties of tropically discretized and max-plus negative feedback models are investigated. Reviewing the previous study [S. Gibo and H. Ito, J. Theor. Biol. 378, 89 (2015)], the conditions under which the Neimark-Sacker bifurcation occurs are rederived with a different approach from their previous one. Furthermore, for limit cycles of the tropically discretized model, it is found that ultradiscrete state emerges when the time interval in the model becomes large. For the max-plus model, we find the two limit cycles; one is stable and the other is unstable. The dynamical properties of these limit cycles can be characterized by using the Poincar\'e map method. Relationship between ultradiscrete limit cycle states for the tropically discretized and the max-plus models is also discussed.

nlin.CD↗

arXiv2023

Types and stability of fixed points for positivity-preserving discretized dynamical systems in two dimensions

Relationship for dynamical properties in the vicinity of fixed points between two-dimensional continuous and its positivity-preserving discretized dynamical systems is studied. Based on linear stability analysis, we reveal the conditions under which the dynamical structures of the original continuous dynamical systems are retained in their discretized dynamical systems, and the types of fixed points are identified if they change due to discretization. We also discuss stability of the fixed points in the discrete dynamical systems. The obtained general results are applied to Sel'kov model and Lengyel-Epstein model.

nlin.CD↗

arXiv2022

Relation of stability and bifurcation properties between continuous and ultradiscrete dynamical systems via discretization with positivity: one dimensional cases

Stability and bifurcation properties of one-dimensional discrete dynamical systems with positivity, which are derived from continuous ones by tropical discretization, are studied. The discretized time interval is introduced as a bifurcation parameter in the discrete dynamical systems, and emergence condition of an additional bifurcation, flip bifurcation, is identified. Correspondence between the discrete dynamical systems with positivity and the ultradiscrete ones derived from them is discussed. It is found that the derived ultradiscrete max-plus dynamical systems can retain the bifurcations of the original continuous ones via tropical discretization and ultradiscretization.

nlin.CD↗

arXiv2022

Rigged Hilbert Space Approach for Non-Hermite Systems with Positive Definite Metric

We investigate Dirac's bra-ket formalism based on a rigged Hilbert space for a non-Hermite quantum system with a positive-definite metric. First, the rigged Hilbert space, characterized by positive-definite metric, is established. With the aid of the nuclear spectral theorem for the obtained rigged Hilbert space, spectral expansions are shown for the bra-kets by the generalized eigenvectors of a quasi-Hermite operator. The spectral expansions are utilized to endow the complete bi-orthogonal system and the transformation theory between the Hermite and non-Hermite systems. As an example of application, we show a specific description of our rigged Hilbert space treatment for some parity-time symmetrical quantum systems.

math-ph↗

arXiv2022

Poincare Map Method for Limit Cycles in a Max-Plus Dynamical System

Dynamical properties of limit cycles in a two-dimensional max-plus dynamical system are discussed. We apply a Poincare map method to the limit cycles in order to reveal their stabilities. This method reduces the two dimensional system to a one-dimensional piecewise linear discrete dynamical system composed of the Poincare map and its cross section. Basins for one of the limit cycles are derived by considering the inverse system of the original model. It is found that the obtained basins show a hierarchic structure. Relationship between the Poincare map method and the method of piecewise linear mapping studied in integrable system theory for the limit cycles is discussed.

nlin.CD↗

arXiv2021

Periodicity of limit cycles in a max-plus dynamical system

By introducing a max-plus dynamical system having limit cycles, we discuss their periodicity, especially the number of discrete states in them. We also find that quasi-periodic cycles exist depending on the bifurcation parameter in the system. Approximate relations between the number of states in the limit cycles and the value of the bifurcation parameter are proposed.

nlin.CD↗

arXiv2021

Dynamical properties of max-plus equations obtained from tropically discretized Sel'kov model

Max-plus equations are derived from tropically discretized Sel'kov model via ultradiscretization. These max-plus equations possess common dynamical structures with the discretized model: Neimark-Sacker bifurcation and limit cycles. The limit cycles of the ultradiscrete max-plus equations have seven discrete states. Furthermore, these max-plus equations exhibit excitability. Relationship between the tropically discretized model and the derived max-plus equations is also discussed based on numerical results. It is found that the derived max-plus equations correspond to a limiting case of the tropically discretized model.

nlin.CD↗

arXiv2021

A simple model for ultradiscrete Hopf bifurcation

Dynamical properties of ultradiscrete Hopf bifurcation, similar to those of the standard Hopf bifurcation, are discussed by proposing a simple model of ultradiscrete equations with max-plus algebra. In ultradiscrete Hopf bifurcation, limit cycles emerge depending on the value of a bifurcation parameter in the model. The limit cycles are composed of a finite number of discrete states. Furthermore, the model exhibits excitability. The model is derived from two different dynamical models with Hopf bifurcation by means of ultradiscretization; it is a candidate for a normal form for ultradiscrete Hopf bifurcation.

nlin.CD↗

arXiv2020

Ultradiscrete Bifurcations for One Dimensional Dynamical Systems

Bifurcations of one dimensional dynamical systems are discussed based on some ultradiscrete equations. The ultradiscrete equations are derived from normal forms of one-dimensional nonlinear differential equations, each of which has saddle-node, transcritical, or supercritical pitchfork bifurcations. An additional bifurcation, which is similar to flip bifurcation, is found in ultradiscrete equations for supercritical pitchfork bifurcation. Dynamical properties of these ultradiscrete bifurcations can be characterized with graphical analysis. As an example of application of our treatment, we focus on an ultradiscrete equation of FitzHugh-Nagumo model, and discuss its dynamical properties.

nlin.CD↗