Asymptotic Harmonic Analysis on the Space of Square Complex Matrices

A Lévy-Khinchin Formula for the Space of Infinite Dimensional Square Complex Matrices

Using a generalised Bochner type representation for Olshanski spherical pairs, we establish a Lévy-Khinchin formula for the continuous functions of negative type on the space $V_\infty= M(\infty, \mathbb C)$ of infinite dimensional square complex matrices relatively to the action of the product group $K_\infty=U(\infty)\times U(\infty)$. The space $V_\infty$ is the inductive limit of the spaces $V_n=M(n, \mathbb C)$, and the group $K_\infty$ is the inductive limit of the product groups $K_n=U(n)\times U(n)$, where $U(n)$ is the unitary group.

具有受限调和支撑的平方和多项式 Gram 矩阵的结构

The structure of Gram matrices of sum of squares polynomials with restricted harmonic support

本文利用 Gram 矩阵结构将 $SL(2)$ 与 $SO(2)$ 的表示论联系起来，证明存在于 $SO(2)$ 不变子空间的平方和多项式具有存在于 $SL(2)$ 特定不变子空间的半正定 Gram 矩阵。

Decompositions of Matrices into Potent and Square-Zero Matrices

In order to find a suitable expression of an arbitrary square matrix over an arbitrary finite commutative ring, we prove that every such a matrix is always representable as a sum of a potent matrix and a nilpotent matrix of order at most two when the Jacobson radical of the ring has zero-square. This somewhat extends results of ours in Lin. & Multilin. Algebra (2021) established for matrices considered on arbitrary fields. Our main theorem also improves on recent results due to Abyzov et al. in Mat. Zametki (2017), Šter in Lin. Algebra & Appl. (2018) and Shitov in Indag. Math. (2019).

Discriminant of symmetric matrices as a sum of squares and the orthogonal group

It is proved that the discriminant of $n\times n$ real symmetric matrices can be written as a sum of squares, where the number of summands equals the dimension of the space of $n$-variable spherical harmonics of degree $n$. The representation theory of the orthogonal group is applied to express the discriminant of three by three real symmetric matrices as a sum of five squares, and to show that it can not be written as the sum of less than five squares. It is proved that the discriminant of four by four real symmetric matrices can be written as a sum of seven squares. These improve results of …

Sums of squares of the Littlewood-Richardson coefficients and GL(n)-harmonic polynomials

We consider the example from invariant theory concerning the conjugation action of the general linear group on several copies of the $n \times n$ matrices, and examine a symmetric function which stably describes the Hilbert series for the invariant ring with respect to the multigradation by degree. The terms of this Hilbert series may be described as a sum of squares of Littlewood-Richardson coefficients. A "principal specialization" of the gradation is then related to the Hilbert series of the $\K$-invariant subring in the $\GL_n$-harmonic polynomials, where $\K$ denotes a block diagonal embe…

Miniversal deformations of matrices under *congruence and reducing transformations

V.I. Arnold [Russian Math. Surveys 26(2) (1971) 29-43] constructed a miniversal deformation of a square complex matrix under similarity; that is, a simple normal form to which not only a given square matrix A but all matrices B close to it can be reduced by similarity transformations that smoothly depend on the entries of B. We give miniversal deformations of matrices of sesquilinear forms; that is, of square complex matrices under *congruence, and construct an analytic reducing transformation to a miniversal deformation. Analogous results for matrices under congruence were obtained by the aut…