Hardy-type spaces for eigenfunctions of invariant differential operators on homogeneous line bundles over Hermitian symmetric spaces

We prove a Fatou-type theorem on a homogeneous line bundle over a Hermitian symmetric space, and characterize the range of the Poisson transform of L_p -functions on the maximal boundary as a Hardy-type space.     

Darboux transformations and recursion operators for differential-difference equations

We review two concepts directly related to the Lax representations of integrable systems: Darboux transformations and recursion operators. We present an extensive list of integrable differential-difference equations with their Hamiltonian structures, recursion operators, nontrivial generalized symmetries, and Darboux-Lax representations. The new results include multi-Hamiltonian structures and recursion operators for integrable Volterra-type equations and integrable discretizations of derivative nonlinear Schrödinger equations such as the Kaup-Newell, Chen-Lee-Liu, and Ablowitz-Ramani-Segur (Gerdjikov-Ivanov) lattices. We also compute the weakly nonlocal inverse recursion operators.     

Completely integrable equations on homogeneous spaces

Completely integrable linear Pfaff systems are investigated, and some of their generalizations to manifolds M=G/, where G is a Lie group and is a discrete subgroup of G, are studied. The reducibility of such a system to a system with constant coefficients with respect to a natural parallelism on M is considered.Translated from Matematicheskie Zametki, Vol. 9, No. 4, pp. 365–373, April, 1971.     

Generating operators for integrable nonlinear evolution equations

For linear problems which are associated with known, exactly integrable nonlinear evolution equations, one gives the corresponding integrodifferential Λ-operators. Relative to the expansions with respect to the elgenfunctions of Λ-operators, the method of the inverse scattering problem can be considered as the analog of the Fourier transform of linear problems, while the Λ-operators are the analogues of the differentiation operator. One considers the equations: Koteweg-de Vries, the nonlinear Schrödinger equations, the nonlinear Schrödinger equations with a derivative, the system of three waves, the matricial analog of the KdV equation, the Toda chain equation.     

Differential equations and recursion relations for Laguerre functions on symmetric cones

We obtain the differential equation and recurrence relations satisfied by the Laguerre functions on an arbitrary symmetric cone .

     

Existence of Conservation Laws and characterization of recursion operators for completely integrable systems

Using the Spencer-Goldschmidt version of the Cartan-Kähler theorem, we give conditions for (local) existence of conservation laws for analytical quasi-linear systems of two independent variables. This result is applied to characterize the recursion operator (in the sense of Magri) of completely integrable systems.

     

Graded differential equations and their deformations: A computational theory for recursion operators

An algebraic model for nonlinear partial differential equations (PDE) in the category ofn-graded modules is constructed. Based on the notion of the graded Frölicher-Nijenhuis bracket, cohomological invariants H ^* (A) are related to each object (A, ) of the theory. Within this framework, H ⁰ (A) generalizes the Lie algebra of symmetries for PDE's, while H ¹ (A) are identified with equivalence classes of infinitesimal deformations. It is shown that elements of a certain part of H ¹ (A) can be interpreted as recursion operators for the object (A, ), i.e. operators giving rise to infinite series of symmetries. Explicit formulas for computing recursion operators are deduced. The general theory is illustrated by a particular example of a graded differential equation, i.e. the Super KdV equation.Tverskoy-Yamskoy per. 14, Apt. 45, 125047 Moscow, Russia.     

Symplectic Dirac operators on Hermitian symmetric spaces

We describe the shape of the symplectic Dirac operators on Hermitian symmetric spaces. For this, we consider these operators as families of operators that can be handled more easily than the original ones.     

Eigenvalue estimates for operators on symmetric Banach sequence spaces

Using abstract interpolation theory, we study eigenvalue distribution problems for operators on complex symmetric Banach sequence spaces. More precisely, extending two well-known results due to König on the asymptotic eigenvalue distribution of operators on -spaces, we prove an eigenvalue estimate for Riesz operators on -spaces with , which take values in a -concave symmetric Banach sequence space , as well as a dual version, and show that each operator on a -convex symmetric Banach sequence space , which takes values in a -concave symmetric Banach sequence space , is a Riesz operator with a sequence of eigenvalues that forms a multiplier from into . Examples are presented which among others show that the concavity and convexity assumptions are essential.

     

Rational curves on moduli spaces of vector bundles

We identify the spaces Hom_i(ℙ¹,M) fori = 1, 2, whereM is the moduli space of vector bundles of rank 2 and determinant isomorphic to ,x ₀ ∈X, on a compact Riemann surface of genusg ≥ 2.     

Isometries and Hermitian operators on complex symmetric sequence spaces

We consider a complex symmetric sequence space E that possesses the Fatou property and is different from l₂. We prove that, for every surjective linear isometry V on E, there exist λ _n ∈ ? with |λ _n | = 1 and a bijective mapping π on the set ? of natural numbers such that

$$V\left( {\left\{ {\xi _n } \right\}_{n \in \mathbb{N}} } \right) = \left\{ {\lambda _n \xi _{\pi (n)} } \right\}_{n \in \mathbb{N}}$$

for every {ξ _n {_n∈? ∈ E.

     

Completely positive compact operators on non-commutative symmetric spaces

Under natural conditions, it is shown that a completely positive operator between two non-commutative symmetric spaces of τ-measurable operators which is dominated in the sense of complete positivity by a completely positive compact operator is itself compact.     

Trace formulas for nuclear operators in spaces of Bochner integrable functions

The paper is devoted to trace formulas for nuclear operators in spaces of Bochner integrable functions. We characterise nuclearity for integral operators on such spaces and develop a trace formula for general kernels applying vector-valued maximal functions.     

A note on the surjectivity of operators on vector bundles over discrete spaces

In this note we give a short and self-contained proof for a criterion of Eidelheit on the solvability of linear equations in infinitely many variables. We use this criterion to study the surjectivity of magnetic Schrödinger operators on bundles over graphs.     

Invariant differential operators on Hermitian symmetric spaces and their eigenvalues

Let be the invariant Cauchy Riemann operator and the corresponding invariant Laplacians on a bounded symmetric domain. We calculate the eigenvalues ofM _m on spherical functions. In particular we prove that for a symmetric domain of rank two the operatorsM ₁,M ₃ generate all invariant differential operators. We also find the eigenvalues of the generators introduced by Shimura.     

Nonlocal symmetries and recursion operators: Partial differential and differential-difference equations

A systematic method to derive the nonlocal symmetries for partial differential and differential-difference equations with two independent variables is presented and shown that the Korteweg-de Vries (KdV) and Burger's equations, Volterra and relativistic Toda (RT) lattice equations admit a sequence of nonlocal symmetries. An algorithm, exploiting the obtained nonlocal symmetries, is proposed to derive recursion operators involving nonlocal variables and illustrated it for the KdV and Burger's equations, Volterra and RT lattice equations and shown that the former three equations admit factorisable recursion operators while the RT lattice equation possesses (2×2) matrix factorisable recursion operator. The existence of nonlocal symmetries and the corresponding recursion operator of partial differential and differential-difference equations does not always determine their mathematical structures, for example, bi-Hamiltonian representation.