arXiv subjects

A. M. Grundland

Publications and source records attributed to A. M. Grundland.

At least 37 records · Page 2Linked to original sources

arXiv2011

Surfaces immersed in Lie algebras associated with elliptic integrals

The main aim of this paper is to study soliton surfaces immersed in Lie algebras associated with ordinary differential equations (ODE's) for elliptic functions. That is, given a linear spectral problem for such an ODE in matrix Lax representation, we search for the most general solution of the wave function which satisfies the linear spectral problem. These solutions allow for the explicit construction of soliton surfaces by the Fokas-Gel'fand formula for immersion, as formulated in (Grundland and Post 2011) which is based on the formalism of generalized vector fields and their prolongation structures. The problem has been reduced to examining three types of symmetries, namely, a conformal symmetry in the spectral parameter (known as the Sym-Tafel formula), gauge transformations of the wave function and generalized symmetries of the associated integrable ODE. The paper contains a detailed explanation of the immersion theory of surfaces in Lie algebras in connection with ODE's as well as an exposition of the main tools used to study their geometric characteristics. Several examples of the Jacobian and P-Weierstrass elliptic functions are included as illustrations of the theoretical results.

math-ph↗

arXiv2011

Soliton surfaces associated with generalize symmetries of integrable equations

In this paper, based on the Fokas, Gel'fand et al approach [15,16], we provide a symmetry characterization of continuous deformations of soliton surfaces immersed in a Lie algebra using the formalism of generalized vector fields, their prolongation structure and links with the Fréchet derivatives. We express the necessary and sufficient condition for the existence of such surfaces in terms of the invariance criterion for generalized symmetries and identify additional sufficient conditions which admit an explicit integration of the immersion functions of 2D surfaces in Lie algebras. We discuss in detail the $su(N)$-valued immersion functions generated by conformal symmetries of the $CP^{N-1}$ sigma model defined on either the Minkowski or Euclidean space. We further show that the sufficient conditions for explicit integration of such immersion functions impose additional restrictions on the admissible conformal symmetries of the model defined on Minkowski space. On the other hand, the sufficient conditions are identically satisfied for arbitrary conformal symmetries of finite action solutions of the $CP^{N-1}$ sigma model defined on Euclidean space.

math-ph↗

arXiv2010

On the surfaces associated with $\mathbb{C}P^{N-1}$ models

We study certain new properties of 2D surfaces associated with the $\mathbb{C}P^{N-1}$ models and the wave functions of the corresponding linear spectral problem. We show that $su(N)$-valued immersion functions expressed in terms of rank-1 orthogonal projectors are linearly dependent, but they span an $(N-1)$-dimensional subspace of the Lie algebra $su(N)$. Their minimal polynomials are cubic, except for the holomorphic and antiholomorphic solutions, for which they reduce to quadratic trinomials. We also derive the counterparts of these relations for the wave functions of the linear spectral problems. In particular, we provide a relation between the wave functions, which results from the partition of unity into the projectors. Finally, we show that the angle between any two position vectors of the immersion functions, corresponding to the same values of the independent variables, does not depend on those variables.

nlin.SI↗

arXiv2010

Analysis of $CP^{N-1}$ sigma models via projective structure

In this paper, we study rank-1 projector solutions to the completely integrable Euclidean $CP^{N-1}$ sigma model in two dimension and their associated surfaces immersed in the $su(N)$ Lie algebra. We reinterpret and generalize the proof of A.M. Din and W.J. Zakzrewski [1980] that any solution for the $CP^{N-1}$$ sigma model defined on the Riemann sphere with finite action can be written as a raising operator acting on a holomorphic one, or a lowering operator acting on a antiholomorphic one. Our proof is formulated in terms of rank-1 Hermitian projectors so it is explicitly gauge invariant and gives new results on the structure of the corresponding sequence of rank-1 projectors. Next, we analyze surfaces associated with the $CP^{N-1}$ models defined using the Generalized Weierstrass Formula for immersion, introduced by B. Konopelchenko [1996]. We show that the surfaces are conformally parameterized by the Lagrangian density with finite area equal to the action of the model and express several other geometrical characteristics of the surface in terms of the Lagrangian density and topological charge density of the model. We demonstrate that any such surface must be orthogonal to the sequence of projectors defined by repeated application of the raising and lowering operators. Finally, we provide necessary and sufficient conditions that a surface be related to a $CP^{N-1}$ sigma model.

math.AP↗

arXiv2010

Invariant formulation of surfaces associated with $CP^{N-1}$ models

In this paper, we provide an invariant formulation of completely integrable $CP^{N-1}$ Euclidean sigma models in two dimensions defined on the Riemann sphere $S^2$. The scaling invariance is explicitly taken into account by expressing all the equations in terms of projection operators. Properties of the projectors mapping onto one-dimensional subspaces are discussed in detail. The paper includes a discussion of surfaces connected with the $CP^{N-1}$ models and the wave functions of their linear spectral problem.

math-ph↗

arXiv2009

Invariant solutions of the supersymmetric sinh-Gordon equation

A systematic group-theoretical analysis of the supersymmetric sinh-Gordon equation is performed. A generalization of the method of prolongations is used to determine the Lie superalgebra of symmetries, and the method of symmetry reduction is applied in order to obtain invariant solutions of the supersymmetric sinh-Gordon equation. The results are compared with those previously found for the supersymmetric sine-Gordon equation. The presence of nonstandard invariants is discussed for the supersymmetric sinh-Gordon equation, as well as for the supersymmetric Korteweg-de Vries equation.

math-ph↗

arXiv2009

Invariant recurrence relations for CP^(N-1) models

In this paper, we present invariant recurrence relations for the completely integrable CP^(N-1) Euclidean sigma model in two dimensions defined on the Riemann sphere S^2 when its action functional is finite. We determine the links between successive projection operators, wave functions of the linear spectral problem, and immersion functions of surfaces in the su(N) algebra together with outlines of the proofs. Our formulation preserves the conformal and scaling invariance of these quantities. Certain geometrical aspects of these relations are described. We also discuss the singularities of meromorphic solutions of the CP^(N-1) model and show that they do not affect the invariant quantities. We illustrate the construction procedure through the examples of the CP^2 and CP^3 models.

math-ph↗

arXiv2009

Invariant solutions of the supersymmetric sine-Gordon equation

A comprehensive symmetry analysis of the N=1 supersymmetric sine-Gordon equation is performed. Two different forms of the supersymmetric system are considered. We begin by studying a system of partial differential equations corresponding to the coefficients of the various powers of the anticommuting independent variables. Next, we consider the super-sine-Gordon equation expressed in terms of a bosonic superfield involving anticommuting independent variables. In each case, a Lie (super)algebra of symmetries is determined and a classification of all subgroups having generic orbits of codimension 1 in the space of independent variables is performed. The method of symmetry reduction is systematically applied in order to derive invariant solutions of the supersymmetric model. Several types of algebraic, hyperbolic and doubly periodic solutions are obtained in explicit form.

math-ph↗

arXiv2009

On analytic descriptions of two-dimensional surfaces associated with the CP^(N-1) sigma model

We study analytic descriptions of conformal immersions of the Riemann sphere S^2 into the CP^(N-1) sigma model. In particular, an explicit expression for two-dimensional (2-D) surfaces, obtained from the generalized Weierstrass formula, is given. It is also demonstrated that these surfaces coincide with the ones obtained from the Sym-Tafel formula. These two approaches correspond to parametrizations of one and the same surface in R^(N^2-1).

math.DG↗

arXiv2009

Surfaces obtained from CP^(N-1) sigma models

In this paper, the Weierstrass technique for harmonic maps S^2 -> CP^(N-1) is employed in order to obtain surfaces immersed in multidimensional Euclidean spaces. It is shown that if the CP^(N-1) model equations are defined on the sphere S^2 and the associated action functional of this model is finite, then the generalized Weierstrass formula for immersion describes conformally parametrized surfaces in the su(N) algebra. In particular, for any holomorphic or antiholomorphic solution of this model the associated surface can be expressed in terms of an orthogonal projector of rank (N-1). The implementation of this method is presented for two-dimensional conformally parametrized surfaces immersed in the su(3) algebra. The usefulness of the proposed approach is illustrated with examples, including the dilation-invariant meron-type solutions and the Veronese solutions for the CP^2 model. Depending on the location of the critical points (zeros and poles) of the first fundamental form associated with the meron solution, it is shown that the associated surfaces are semi-infinite cylinders. It is also demonstrated that surfaces related to holomorphic and mixed Veronese solutions are immersed in R^8 and R^3, respectively.

math.DG↗

arXiv2009

Elliptic solutions of isentropic ideal compressible fluid flow in (3+1) dimensions

A modified version of the conditional symmetry method, together with the classical method, is used to obtain new classes of elliptic solutions of the isentropic ideal compressible fluid flow in (3+1) dimensions. We focus on those types of solutions which are expressed in terms of the Weierstrass P-functions of Riemann invariants. These solutions are of special interest since we show that they remain bounded even when these invariants admit the gradient catastrophe. We describe in detail a procedure for constructing such classes of solutions. Finally, we present several examples of an application of our approach which includes bumps, kinks and multi-wave solutions.

math-ph↗

arXiv2008

N=2 supersymmetric extension of a hydrodynamic system in Riemann invariants

In this paper, we formulate an N=2 supersymmetric extension of a hydrodynamic-type system involving Riemann invariants. The supersymmetric version is constructed by means of a superspace and superfield formalism, using bosonic superfields, and consists of a system of partial differential equations involving both bosonic and fermionic variables. We make use of group-theoretical methods in order to analyze the extended model algebraically. Specifically, we calculate a Lie superalgebra of symmetries of our supersymmetric model and make use of a general classification method to classify the one-dimensional subalgebras into conjugacy classes. As a result we obtain a set of 401 one-dimensional nonequivalent subalgebras. For selected subalgebras, we use the symmetry reduction method applied to Grassmann-valued equations in order to determine analytic exact solutions of our supersymmetric model. These solutions include travelling waves, bumps, kinks, double-periodic solutions and solutions involving exponentials and radicals.

math-ph↗

arXiv2008

Supersymmetric version of a hydrodynamic system in Riemann invariants and its solutions

In this paper, a supersymmetric extension of a system of hydrodynamic type equations involving Riemann invariants is formulated in terms of a superspace and superfield formalism. The symmetry properties of both the classical and supersymmetric versions of this hydrodynamical model are analyzed through the use of group-theoretical methods applied to partial differential equations involving both bosonic and fermionic variables. More specifically, we compute the Lie superalgebras of both models and perform classifications of their respective subalgebras. A systematic use of the subalgebra structures allow us to construct several classes of invariant solutions, including travelling waves, centered waves and solutions involving monomials, exponentials and radicals.

math-ph↗

arXiv2007

Supersymmetric version of a Gaussian irrotational compressible fluid flow

The Lie point symmetries and corresponding invariant solutions are obtained for a Gaussian, irrotational, compressible fluid flow. A supersymmetric extension of this model is then formulated through the use of a superspace and superfield formalism. The Lie superalgebra of this extended model is determined and a classification of its subalgebras is performed. The method of symmetry reduction is systematically applied in order to derive special classes of invariant solutions of the supersymmetric model. Several new types of algebraic, hyperbolic, multi-solitonic and doubly periodic solutions are obtained in explicit form.

math-ph↗

arXiv2007

Conformally parametrized surfaces associated with CP^(N-1) sigma models

Two-dimensional conformally parametrized surfaces immersed in the su(N) algebra are investigated. The focus is on surfaces parametrized by solutions of the equations for the CP^(N-1) sigma model. The Lie-point symmetries of the CP^(N-1) model are computed for arbitrary N. The Weierstrass formula for immersion is determined and an explicit formula for a moving frame on a surface is constructed. This allows us to determine the structural equations and geometrical properties of surfaces in R^(N^2-1). The fundamental forms, Gaussian and mean curvatures, Willmore functional and topological charge of surfaces are given explicitly in terms of any holomorphic solution of the CP^2 model. The approach is illustrated through several examples, including surfaces immersed in low-dimensional su(N) algebras.

math.DG↗

arXiv2006

On Conditionally Invariant Solutions of Magnetohydrodynamic Equations

We present a version of the conditional symmetry method in order to obtain multiple wave solutions expressed in terms of Riemann invariants. We construct an abelian distribution of vector fields which are symmetries of the original system of PDEs subjected to certain first order differential constraints. The usefulness of our approach is demonstrated on simple and double wave solutions of MHD equations. The paper also contains a comparison of the conditional symmetry method with the generalized method of characteristics. Received 19 April, 2003; Accepted 10 June, 2003 Final Version published in J. Nonlinear Math. Phys. 11,1 47-74, (2004).

math-ph↗

arXiv2006

Surfaces associated with theta function solutions of the periodic 2D-Toda lattice

The objective of this paper is to present some geometric aspects of surfaces associated with theta function solutions of the periodic 2D-Toda lattice. For this purpose we identify the $(N^2-1)$-dimensional Euclidean space with the ${\frak su}(N)$ algebra which allows us to construct the generalized Weierstrass formula for immersion for such surfaces. The elements characterizing surface like its moving frame, the Gauss-Weingarten and the Gauss-Codazzi-Ricci equations, the Gaussian curvature, the mean curvature vector and the Wilmore functional of a surface are expressed explicitly in terms of any theta function solution of the Toda lattice model. We have shown that these surfaces are all mapped into subsets of a hypersphere in $\mathbb{R}^{N^2-1}$. A detailed implementations of the obtained results are presented for surfaces immersed in the ${\frak su}(2)$ algebra and we show that different Toda lattice data correspond to different subsets of a sphere in $\mathbb{R}^3$.

math.DG↗

arXiv2006

Surfaces associated with sigma models and the sine-Gordon equation

We present a unified method of construction of surfaces associated with Grassmannian sigma models, expressed in terms of an orthogonal projector. This description leads to compact formulae for structural equations of two-dimensional surfaces immersed in the su(N) algebra. In the special case of the CP^1 sigma model we obtain constant negative Gaussian curvature surfaces. As a consequence, this leads us to an explicit relation between the CP^1 sigma model and the sine-Gordon equation.

math.DG↗