arXiv subjects

Taras Skrypnyk

Publications and source records attributed to Taras Skrypnyk.

7 recordsLinked to original sources

arXiv2025

On compatible linear and quadratic Poisson brackets on $gl(N)$

In the present paper, using two constant tensors $c$ and $b$ on $sl(N)\otimes sl(N)$ satisfying certain linear-quadratic equation and a technique of Poisson bivectors and Schouten brackets, we explicitly construct quadratic Poisson bracket on the space $ (sl(N)+\mathbb{C})^*$ which is compatible with the standard Lie--Poisson bracket on $gl(N)^* \simeq (sl(N)\oplus \mathbb{C})^*$. The case of $N=3$ is considered in details. The relation of the proposed brackets with the generalized classical Sklyanin algebras is explained.

math-ph↗

arXiv2025

Symmetric Separation of Variables for the Extended Clebsch and Manakov Models

In the present paper, using a modification of the method of vector fields $Z_i$ of the bi-Hamiltonian theory of separation of variables (SoV), we construct symmetric non-Stäckel variable separation for three-dimensional extension of the Clebsch model, which is equivalent (in the bi-Hamiltonian sense) to the system of interacting Manakov (Schottky-Frahm) and Euler tops. For the obtained symmetric SoV (contrary to the previously constructed asymmetric one), all curves of separation are the same and have genus five. It occurred that the difference between the symmetric and asymmetric cases is encoded in the different form of the vector fields $Z$ used to construct separating polynomial. We explicitly construct coordinates and momenta of separation and Abel-type equations in the considered examples of symmetric SoV for the extended Clebsch and Manakov models.

nlin.SI↗

arXiv2025

Algebro-geometric integration of the Boussinesq hierarchy

We construct an integrable hierarchy of the Boussinesq equation using the Lie-algebraic approach of Holod-Flashka-Newell-Ratiu. We show that finite-gap hamiltonian systems of the hierarchy arise on coadjoint orbits in the loop algebra of $\mathfrak{sl}(3)$, and possess spectral curves from the family of $(3,3N\,{+}\,1)$-curves, $N\,{\in}\, \Natural$. Separation of variables leads to the Jacobi inversion problem on the mentioned curves, which is solved in terms of the corresponding multiply periodic functions. An exact finite-gap solution of the Boussinesq equation is obtained explicitly, and a conjecture on the reality conditions is made. The obtained solutions are computed for several spectral curves, and illustrated graphically.

nlin.SI↗

arXiv2022

The Generalized Lipkin-Meshkov-Glick Model and the Modified Algebraic Bethe Ansatz

We show that the Lipkin-Meshkov-Glick $2N$-fermion model is a particular case of one-spin Gaudin-type model in an external magnetic field corresponding to a limiting case of non-skew-symmetric elliptic $r$-matrix and to an external magnetic field directed along one axis. We propose an exactly-solvable generalization of the Lipkin-Meshkov-Glick fermion model based on the Gaudin-type model corresponding to the same $r$-matrix but arbitrary external magnetic field. This model coincides with the quantization of the classical Zhukovsky-Volterra gyrostat. We diagonalize the corresponding quantum Hamiltonian by means of the modified algebraic Bethe ansatz. We explicitly solve the corresponding Bethe-type equations for the case of small fermion number $N=1,2$.

nlin.SI↗

arXiv2021

Separation of Variables, Quasi-Trigonometric $r$-Matrices and Generalized Gaudin Models

We construct two new one-parametric families of separated variables for the classical Lax-integrable Hamiltonian systems governed by a one-parametric family of non-skew-symmetric, non-dynamical $\mathfrak{gl}(2)\otimes \mathfrak{gl}(2)$-valued quasi-trigonometric classical $r$-matrices. We show that for all but one classical $r$-matrices in the considered one-parametric families the corresponding curves of separation differ from the standard spectral curve of the initial Lax matrix. The proposed scheme is illustrated by an example of separation of variables for $N=2$ quasi-trigonometric Gaudin models in an external magnetic field.

nlin.SI↗

arXiv2020

New Separation of Variables for the Classical XXX and XXZ Heisenberg Spin Chains

We propose a non-standard separation of variables for the classical integrable XXX and XXZ spin chains with degenerate twist matrix. We show that for the case of such twist matrices one can interchange the role of classical separating functions $A(u)$ and $B(u)$ and construct a new full set of separated variables, satisfying simpler equation of separation and simpler Abel equations in comparison with the standard separated variables of Sklyanin. We show that for certain cases of the twist matrices the constructed separated variables can be directly identified with action-angle coordinates.

math-ph↗

arXiv2015

The Clebsch System

The Clebsch system is one of the few classical examples of rigid bodies whose equations of motion are known to be integrable in the sense of Liouville. The explicit solution of its equations of motion, however, is particularly hard, and it has defeated many attempts in the past. In this paper we present a novel and rather detailed study of these equations of motion. Our approach is based on an improved version of the method originally used, in 1889, by Sophia Kowalewski to solve the equations of motion of the top bearing her name. We improve her method in two important points, and we clarify that it concerns a class of dynamical systems which is wider than the class of Hamiltonian systems which are integrable in the sense of Liouville. We use the improved version of the method by Kowalewski to prove two results. First, without using the Hamiltonian structure of the Clebsch system, we show that the integration of the equations of motion may be achieved by computing four Abelian integrals. Next, taking into account its Hamiltonian structure, we show that two quadratures are sufficient to compute a complete integral of its Hamilton-Jacobi equation. In this way, the process of solution of the equations of motion of the Clebsch system is clarified both from the standpoint of Abel and from the standpoint of Jacobi.

nlin.SI↗