Vandermonde-like determinants’ representations of Darboux transformations and explicit solutions for the modified Kadomtsev-Petviashvili equation

Recently, the (2+1)-dimensional modified Kadomtsev-Petviashvili (mKP) equation was decomposed into two known (1+1)-dimensional soliton equations by Dai and Geng [H.H. Dai, X.G. Geng, J. Math. Phys. 41 (2000) 7501]. In the present paper, a systematic and simple method is proposed for constructing three kinds of explicit N-fold Darboux transformations and their Vandermonde-like determinants’ representations of the two known (1+1)-dimensional soliton equations based on their Lax pairs. As an application of the Darboux transformations, three explicit multi-soliton solutions of the two (1+1)-dimensional soliton equations are obtained; in particular six new explicit soliton solutions of the (2+1)-dimensional mKP equation are presented by using the decomposition. The explicit formulas of all the soliton solutions are also expressed by Vandermonde-like determinants which are remarkably compact and transparent.     

On symmetry preserving and symmetry broken bright,dark and antidark soliton solutions of nonlocal nonlinear Schrödinger equation

We construct symmetry preserving and symmetry broken N-bright, dark and antidark soliton solutions of a nonlocal nonlinear Schrödinger equation. To obtain these solutions, we use appropriate eigenfunctions in Darboux transformation (DT) method. We present explicit one and two bright soliton solutions and show that they exhibit stable structures only when we combine the field and parity transformed complex conjugate field. Further, we derive two dark/antidark soliton solution with the help of DT method. Unlike the bright soliton case, dark/antidark soliton solution exhibits stable structure for the field and the parity transformed conjugate field separately. In the dark/antidark soliton solution case we observe a contrasting behaviour between the envelope of the field and parity transformed complex conjugate envelope of the field. For a particular parametric choice, we get dark (antidark) soliton for the field while the parity transformed complex conjugate field exhibits antidark (dark) soliton. Due to this surprising result, both the field and PT transformed complex conjugate field exhibit sixteen different combinations of collision scenario. We classify the parametric regions of dark and antidark solitons in both the field and parity transformed complex conjugate field by carrying out relevant asymptotic analysis. Further we present 2N-dark/antidark soliton solution formula and demonstrate that this solution may have $2^{2N}\times 2^{2N}$ combinations of collisions.     

Self-splitting of multisoliton bound states in planar Kerr waveguides

We address the phenomenon of self-splitting of N-soliton bound states into their individual soliton constituents in a planar Kerr medium with a waveguide that has a triangular linear refractive index. The splitting is due to the fact that each soliton component experiences different change of propagation angle which is driven by the potential introduced by the refractive index variation and the soliton amplitude. Our numerical simulations show that the break up only disturbs the propagation angle of each single soliton constituent but not its amplitude.     

Explicit N-fold Darboux transformation for the classical Boussinesq system and multi-soliton solutions

In this Letter, a systematic method is presented to construct the N-fold Darboux transformation with multi-parameters for a spectral problem associated with a classical Boussinesq system. As an application, we obtain the new soliton solutions of the classical Boussinesq system.     

Searching for new conditions for fermion N-representability

New elements of the dual cone of the set of fermion N-representable 2-density operators are proposed. So far, the explicit form of the corresponding necessary conditions for N-representability is obtained for N = 3. In this case the new condition is stronger than the known B- and C-conditions for 3-representability. The results provide evidence that in the spectral decomposition of the N-representable 2-density operator there exists an intrinsic relation between the eigenvalue and the corresponding eigenfunction.     

Stability and quasi-equidistant propagation of NLS soliton trains

Using the complex Toda chain we model the asymptotic behavior of the N soliton pulse trains of the nonlinear Schrödinger equation. Stable asymptotic regimes are: (i) asymptotically free propagation of all N solitons; (ii) bound state regime where the N solitons may move quasi-equidistantly (QED); and (iii) various intermediate regimes. Our method allows one to determine analytically the set of initial soliton parameters corresponding to each regime. We list the soliton parameters, which ensure QED propagation of all N solitons since this is important for optical fiber communication.     

N-solitons on a vortex filament

We describe a purely algebraic algorithm for finding, in the localized induction approach, three-dimensional vortex motion corresponding to the N-soliton solution of the nonlinear Schrödinger equation. The method used relies essentially up-on the geometric approach to soliton systems and consists in the construction of the corresponding soliton surfaces. For N = 0 and N = 1 we recover the straight line and Hasimoto vortex, respectively, while for N = 2 the algorithm gives a new vortex motion, of higher complexity, which is, presumably, an analytic expression for some scattering phenomena along vortices recently discovered by Browand and Hopfinger.     

Novel multi-band quantum soliton states for a derivative nonlinear Schrödinger model

We show that localized N-body soliton states exist for a quantum integrable derivative nonlinear Schrödinger model for several nonoverlapping ranges (called bands) of the coupling constant η. The number of such distinct bands is given by Euler's φ-function which appears in the context of number theory. The ranges of η within each band can also be determined completely using concepts from number theory such as Farey sequences and continued fractions. We observe that N-body soliton states appearing within each band can have both positive and negative momentum. Moreover, for all bands lying in the region η>0, soliton states with positive momentum have positive binding energy (called bound states), while the states with negative momentum have negative binding energy (anti-bound states).     

Riemann-Hilbert approach and N-soliton formula for a higher-order Chen-Lee-Liu equation

We consider a higher-order Chen-Lee-Liu (CLL) equation with third order dispersion and quintic nonlinearity terms. In the framework of the Riemann-Hilbert method, we obtain the compact N-soliton formula expressed by determinants. Based on the determinant solution, some properties for single soliton and asymptotic analysis of N-soliton solution are explored. The simple elastic interaction of N solitons is confirmed.     

Cusp and loop soliton solutions of short-wave models for the Camassa–Holm and Degasperis–Procesi equations

A simple method is developed for constructing the solutions of the short-wave model equations associated with the Camassa–Holm (CH) and Degasperis–Procesi (DP) shallow-water wave equations. Taking an appropriate scaling limit of the N-soliton solution of the CH equation, we obtain the N-cusp soliton solution for the CH short-wave model. The similar procedure also leads to the N-loop soliton solution for the DP short-wave model. We describe the property of the solutions. In particular, we derive the large-time asymptotics of the solutions as well as the formulas for the phase shift.     

Dispersive dark optical soliton with Schödinger-Hirota equation by G′/G-expansion approach in power law medium

This paper studies dispersive optical solitons that are governed by the Schrödinger-Hirota equation with power law nonlinearity. The G′/G-expansion method is applied to extract soliton solution to this equation. This approach reveals dark 1-soliton solution to the equation.     

Break up of bound-N-spatial-soliton in a ramp waveguide

We present an analytical and numerical investigation of the propagation of spatial solitons in a nonlinear waveguide with ramp linear refractive index profile (ramp waveguide). For the propagation of a single soliton beam in a ramp waveguide, the particle theory shows that the soliton beam follows a parabolic curve in the region where the linear refractive index increases and a straight line outside the waveguide. The acceleration of the soliton depends on the beam intensity: higher amplitude solitons experience higher acceleration. Numerical calculations using an implicit Crank–Nicolson scheme confirm the result of the particle theory. Combining these propagation properties with the theory about bound-N-soliton, we study the break up of such a bound-N-soliton in a ramp waveguide. In a ramp waveguide, a bound-N-soliton will always be splitted into N independent solitons with the higher amplitude soliton emitted first. The amplitude of the separated solitons after break up are calculated using the soliton theory as if the solitons are independent. Numerical simulations show that the results agree quite well with this theoretical prediction, indicating that the interaction during break up has only little influence.     

The determinant representation of an N-fold Darboux transformation for the short pulse equation

We present an explicit representation of an N-fold Darboux transformation T?_N for the short pulse equation, by the determinants of the eigenfunctions of its Lax pair. In the course of the derivation of T?_N, we show that the quasi-determinant is avoidable, and it is contrast to a recent paper (J. Phys. Soc. Jpn. 81 (2012), 094008) by using this relatively new tool which was introduced to study noncommutative mathematical objectives. T?_N produces new solutions u^[N] and x^[N] which are expressed by ratios of two corresponding determinants. We also obtain the soliton solutions, which have a variable trajectory, of the short pulse equation from new “seed” solutions.     

Simulative demonstration of soliton pulse stability over the nonlinear regime in a birefringent optical fiber

In this paper, the results of numerical analysis are demonstrated for sech pulse (soliton) propagation in a birefringent optical fiber using computer modeling and simulation. Here, the initial pulse is polarized linearly and guided into the fiber at an angle of 45° to its polarization axes. The birefringence-induced time delay of 200 and 440 ps between X and Y polarization components has been reported at a fiber length of 631.72 km (10 soliton periods) by considering linear and nonlinear regimes, respectively. The Kerr nonlinearity, which stabilizes solitons against spreading due to GVD, also stabilizes them against splitting due to birefringence. A similar fact is true for the birefringent walk-off. Above a certain soliton order (N_th), the evolution scenario is qualitatively different and two orthogonally polarized components of the soliton move with a common group velocity despite their different modal indices or polarization mode dispersion (PMD) at a fiber length of 631.72 km (10 soliton periods) and 1264.344 km (20 soliton periods) over a nonlinear regime at θ≠45°. The physical effect responsible for this type of behavior is the cross-phase modulation (XPM) between the two polarization components.     

Haldane-like antiferromagnetic spin chain in the large anisotropy limit

We consider the one dimensional, periodic spin chain with N sites, similar to the one studied by Haldane [1], however in the opposite limit of very large anisotropy and small nearest neighbour, anti-ferromagnetic exchange coupling between the spins, which are of large magnitude s. For a chain with an even number of sites we show that actually the ground state is non-degenerate and given by a superposition of the two Neél states, due to quantum spin tunnelling. With an odd number of sites, the Neél state must necessarily contain a soliton. The position of the soliton is arbitrary thus the ground state is N-fold degenerate. This set of states reorganizes into a band. We show that this occurs at order 2s in perturbation theory. The ground state is non-degenerate for integer spin, but degenerate for half-odd integer spin as is required by Kramers' theorem [18].     

Multisoliton solutions of the (2+1)-dimensional Harry Dym equation

The exact N-soliton solutions of the (2+1)-dimensional Harry Dym equation are constructed analytically. Different types of two-soliton interactions are singled out in the general N-soliton solution. The existence of inelastic soliton interaction and two-soliton resonances are shown.     

Integrable aspects and applications of a generalized inhomogeneous N-coupled nonlinear Schrödinger system in plasmas and optical fibers via symbolic computation

For describing the general behavior of N fields propagating in inhomogeneous plasmas and optical fibers, a generalized N-coupled nonlinear Schrödinger system is investigated with symbolic computation in this Letter. When the coefficient functions obey the Painlevé-integrable conditions, the (N+1)×(N+1) nonisospectral Lax pair associated with such a model is derived by means of the Ablowitz-Kaup-Newell-Segur formalism. Furthermore, the Darboux transformation is constructed so that it becomes exercisable to generate the multi-soliton solutions in a recursive manner. Through the graphical analysis of some exact analytic one- and two-soliton solutions, our discussions are focused on the envelope soliton excitation in time-dependent inhomogeneous plasmas and the optical pulse propagation with the constant (or distance-related) fiber gain/loss and phase modulation.     

Multisoliton phase shifts in the case of a nonzero reflection coefficient

We study multisoliton solutions of the Korteweg-de Vries equation in the case of a nonzero reflection coefficient. An explicit phase shift formula is derived that clearly displays the nature of the interaction of each soliton with the other ones and with the dispersive wavetrain. In particular, this formula shows that each soliton experiences in addition to the ordinary N-soliton phase shift an extra phase shift to the left caused by the collision with the dispersive wavetrain.     

Semi-classical spectrum of the homogeneous sine-Gordon theories

The semi-classical spectrum of the homogeneous sine-Gordon theories associated with an arbitrary compact simple Lie group G is obtained and shown to be entirely given by solitons. These theories describe quantum integrable massive perturbations of Gepner's G-parafermions whose classical equations-of-motion are non-abelian affine Toda equations. One-soliton solutions are constructed by embeddings of the SU(2) complex sine-Gordon soliton in the regular SU(2) subgroups of G. The resulting spectrum exhibits both stable and unstable particles, which is a peculiar feature shared with the spectrum of monopoles and dyons in N = 2 and N = 4 supersymmetric gauge theories.     

Comparative investigation and suitability of various data formats for 10 Gb/s optical soliton transmission links at different chirps

This paper presents the comparative investigation and suitability of various data formats for optical soliton transmission links at 10 Gb/s for different chirps (−0.7 to 0.7). Here the investigations focused on data formats: NRZ, RZ soliton, RZ raised cosine and RZ super Gaussian. The comparative results and suitability of data formats is based on various performance measures such as Q-factor, eye opening, BER and jitter. It has been indicated that RZ super Gaussian yields the highest value of Q (34.08 dB), good eye opening and lowest BER.