A1-invariance of non-stable K1-functors in the equicharacteristic case

We apply the techniques developed by I. Panin for the proof of the equicharacteristic case of the Serre–Grothendieck conjecture for isotropic reductive groups (Panin et al., 2015; Panin, 2019) to obtain similar injectivity and ${\mathbb{A}}^1$-invariance theorems for non-stable $K_1$-functors associated to isotropic reductive groups. Namely, let $G$ be a reductive group over a commutative ring $R$. We say that $G$ has isotropic rank $\ge n$, if every non-trivial normal semisimple $R$-subgroup of $G$ contains ${\left({\mathbf{G}}_{m,R}\right)}^n$. We show that if $G$ has isotropic rank $\ge 2$ and $R$ is a regular domain containing a field, then $K_1^G\left(R\left[x\right]\right)=K_1^G\left(R\right)$, where $K_1^G\left(R\right)=G\left(R\right)/E\left(R\right)$ is the corresponding non-stable $K_1$-functor, also called the Whitehead group of $G$. If $R$ is, moreover, local, then we show that $K_1^G\left(R\right)\to K_1^G\left(K\right)$ is injective, where $K$ is the field of fractions of $R$.     

Mixed quantum skew Howe duality and link invariants of type A

We define a ribbon category $\mathsf{Sp}(\beta )$, depending on a parameter β, which encompasses Cautis, Kamnitzer and Morrison's spider category, and describes for $\beta =m?n$ the monoidal category of representations of $U_q({\mathfrak{gl}}_{m|n})$ generated by exterior powers of the vector representation and their duals. We identify this category $\mathsf{Sp}(\beta )$ with a direct limit of quotients of a dual idempotented quantum group ${\dot{\mathbf{U}}}_q({\mathfrak{gl}}_{r+s})$, proving a mixed version of skew Howe duality in which exterior powers and their duals appear at the same time. We show that the category $\mathsf{Sp}(\beta )$ gives a unified natural setting for defining the colored ${\mathfrak{gl}}_{m|n}$ link invariant (for $\beta =m?n$) and the colored HOMFLY-PT polynomial (for β generic).     

On a problem of Specker about Euclidean representations of finite graphs

Say that a graph $G$ is representable in ${\mathbb{R}}^n$ if there is a map $f$ from its vertex set into the Euclidean space ${\mathbb{R}}^n$ such that $6f\left(x\right)?f\left(x^{\prime }\right)6=6f\left(y\right)?f\left(y^{\prime }\right)6$ iff $\{x,x^{\prime }\}$ and$\{y,y^{\prime }\}$ are both edges or both non-edges in $G$. The purpose of this note is to present the proof of the following result, due to Einhorn and Schoenberg in Einhorn and Schoenberg (1966): if $G$ finite is neither complete nor independent, then it is representable in ${\mathbb{R}}^{\left|G\right|?2}$. A similar result also holds in the case of finite complete edge-colored graphs.     

Note on semiclassical states for the Schrödinger equation with nonautonomous nonlinearities

We consider the following Schrödinger equation $-{\hslash }^2\Delta u+V\left(x\right)u=\Gamma \left(x\right)f\left(u\right)\mathrm{in}{\mathbb{R}}^N,$where $u\in H^1\left({\mathbb{R}}^N\right)$, $u>0$, $\hslash >0$ and $f$ is superlinear and subcritical nonlinear term. We show that if $V$ attains local minimum and $\Gamma$ attains global maximum at the same point or $V$ attains global minimum and $\Gamma$ attains local maximum at the same point, then there exists a positive solution for sufficiently small $\hslash >0$.     

The covering radius of the Reed–Muller code RM(2,7) is 40

It was proved by J. Schatz that the covering radius of the second order Reed–Muller code $RM(2,6)$ is 18 (Schatz (1981)). However, the covering radius of $RM(2,7)$ has been an open problem for many years. In this paper, we prove that the covering radius of $RM(2,7)$ is 40, which is the same as the covering radius of $RM(2,7)$ in $RM(3,7)$. As a corollary, we also find new upper bounds for the covering radius of $RM(2,n)$, $n=8,9,10$.     

Minimal surfaces and Schwarz lemma

We prove a sharp Schwarz lemma type inequality for the Weierstrass–Enneper parameterization of minimal disks. It states the following. If $F:\mathbf{D}\to \Sigma$ is a conformal harmonic parameterization of a minimal disk $\Sigma \subset {\mathbf{R}}^3$, where $\mathbf{D}$ is the unit disk and $\left|\Sigma \right|=\pi R^2$, then $\left|F_x\left(z\right)\right|(1-{\left|z\right|}^2)\le R$. If for some $z$ the previous inequality is equality, then the surface is an affine image of a disk, and $F$ is linear up to a Möbius transformation of the unit disk.     

Operator-stable and operator-self-similar random fields

Two classes of multivariate random fields with operator-stable marginals are constructed. The random fields $\mathbb{X}=\{X\left(t\right):t\in {\mathbb{R}}^d\}$ with values in ${\mathbb{R}}^m$ are invariant in law under operator-scaling in both the time-domain and the state-space. The construction is based on operator-stable random measures utilizing certain homogeneous functions.