Nonlinear Sciences

The one-parameter family of second order nonlinear difference equations each of which is given by x n−1 x n x n+1 = x n−1 +( x n ) β−1 + x n+1 (β∈N) is explored. Since the equation above is arising from seed mutations of a rank 2 cluster algebra, its solution is periodic only when β≤3 . In order to evaluate the dynamics with β≥4 , algebraic entropy of the birational map equivalent to the difference equation is investigated; it vanishes when β=4 but is positive when β≥5 . This fact suggests that the difference equation with β≤4 is integrable but that with β≥5 is not. It is moreover shown that the difference equation with β≥4 fails the singularity confinement test. This fact is consistent with linearizability of the equation with β=4 and reinforces non-integrability of the equation with β≥5 .

In this paper, we are concerned with a a semi-discrete complex short pulse (CSP) equation of both focusing and defocusing types, which can be viewed as an analogue to the Ablowitz-Ladik (AL) lattice in the ultra-short pulse regime. By using a generalized Darboux transformation method, various solutions to this newly integrable semi-discrete equation are studied with both zero and nonzero boundary conditions. To be specific, for the focusing CSP equation, the multi-bright solution (zero boundary condition), multi-breather and high-order rogue wave solutions (nonzero boudanry conditions) are derived, while for the defocusing CSP equation with nonzero boundary condition, the multi-dark soliton solution is constructed. We further show that, in the continuous limit, all the solutions obtained converge to the ones for its original CSP equation (see Physica D, 327 13-29 and Phys. Rev. E 93 052227)

A new, completely integrable, two dimensional evolution equation is derived for an ion acoustic wave propagating in a magnetized, collisionless plasma. The equation is a multidimensional generalization of a modulated wavepacket with weak transverse propagation, which has resemblance to nonlinear Schrodinger (NLS) equation and has a connection to Kadomtsev-Petviashvili equation through a constraint relation. Higher soliton solutions of the equation are derived through Hirota bili- nearization procedure, and an exact lump solution is calculated exhibiting 2D structure. Some mathe- matical properties demonstrating the completely integrable nature of this equation are described. Modulational instability using nonlinear frequency correction is derived, and the corresponding growth rate is calculated, which shows the directional asymmetry of the system. The discovery of this novel (2þ1) dimensional integrable NLS type equation for a magnetized plasma should pave a new direction of research in the field.

A new three-dimensional second-order nonlinear wave equation is introduced which passes the Painleve test for integrability and possesses KdV-type multisoliton solutions. Lax integrability of this equation remains unknown.

This is the first part of a two-part paper describing a new concept of separation of variables applied to the Clebsch integrable case of the Kirchhoff equations. There are two principal novelties: 1) Separating coordinates are constructed (not guessed) by solving the Kowalewski separability conditions. 2) The quadratures represent an apparently new generalization of the standard Jacobi inversion problem of algebraic geometry. Part I explains the Kowalewski separability conditions and their implementation to the Clebsch case. It is shown that the new separating coordinates lead to quadratures involving Abelian differentials on two different non-hyperelliptic curves (of genus higher than the dimension of the invariant tori). In Part II these quadratures are interpreted as a new generalization of the standard Abel--Jacobi map, and a procedure of its inversion in terms of theta-functions is worked out. The theta-function solution is different from that found long time ago by F. Kötter, since the theta-functions used in this paper have different period matrix.

This is the second part of a paper describing a new concept of separation of variables applied to the classical Clebsch integrable case. The quadratures obtained in Part I (also uploaded in arXiv.org) lead to a new type of the Abel map which contains Abelian integrals on two different algebraic curves. Here we interprete it as from the product of the two curves to the Prym variety of one of them, show that the map is well defined although not a bijection. We analyse its properties and formulate a new extention of the Riemann vanishing theorem, which allows to invert the map in terms of theta-functions of higher order. Lastly, we describe how to express the original variables of the Clebsch system in terms of the preimages of the map. This enables one to obtain theta-function solution whose structure is different from that found long time ago by F. Kötter.

For cubic pencils we define the notion of an involution curve. This is a curve which intersects each curve of the pencil in exactly one non base-point of the pencil. Involution curves can be used to construct integrable maps of the plane which leave invariant a cubic pencil.

A new matrix modified Korteweg-de Vries (mmKdV) equation with a p×q complex-valued potential matrix function is first studied via Riemann-Hilbert approach, which can be reduced to the well-known coupled modified Korteweg-de Vries equations by selecting special potential matrix. Starting from the special analysis for the Lax pair of this equation, we successfully establish a Riemann-Hilbert problem of the equation. By introducing the special conditions of irregularity and reflectionless case, some interesting exact solutions, including the N -soliton solution formula, of the mmKdV equation are derived through solving the corresponding Riemann-Hilbert problem. Moreover, due to the special symmetry of special potential matrices and the N -soliton solution formula, we make further efforts to classify the original exact solutions to obtain some other interesting solutions which are all displayed graphically. It is interesting that the local structures and dynamic behaviors of soliton solutions, breather-type solutions and bell-type soliton solutions are all analyzed via taking different types of potential matrices.

A new integrable nonlocal nonlinear Schroedinger (NLS) equation with clear physical motivations is proposed. This equation is obtained from a special reduction of the Manakov system, and it describes Manakov solutions whose two components are related by a parity symmetry. Since the Manakov system governs wave propagation in a wide variety of physical systems, this new nonlocal equation has clear physical meanings. Solitons and multi-solitons in this nonlocal equation are also investigated in the framework of Riemann-Hilbert formulations. Surprisingly, symmetry relations of discrete scattering data for this equation are found to be very complicated, where constraints between eigenvectors in the scattering data depend on the number and locations of the underlying discrete eigenvalues in a very complex manner. As a consequence, general N -solitons are difficult to obtain in the Riemann-Hilbert framework. However, one- and two-solitons are derived, and their dynamics investigated. It is found that two-solitons are generally not a nonlinear superposition of one-solitons, and they exhibit interesting dynamics such as meandering and sudden position shifts. As a generalization, other integrable and physically meaningful nonlocal equations are also proposed, which include NLS equations of reverse-time and reverse-space-time types as well as nonlocal Manakov equations of reverse-space, reverse-time and reverse-space-time types.

By applying a simple symmetry reduction on a two-layer liquid model, a nonlocal counterpart of it is obtained. Then a general form of nonlocal nonlinear Schrodinger (NNLS) equation with shifted parity, charge-conjugate and delayed time reversal is obtained by using multi-scale expansion method. Some kinds of elliptic periodic wave solutions of the NNLS equation are obtained by using function expansion method, which contain soliton solutions and kink solutions when the modulus taking as unity. Some representative figures of these solutions are given and analyzed in detail. In addition, by carrying out the classical symmetry method on the NNLS equation, not only the Lie symmetry group but also the related symmetry reduction solutions are given.