Let $X$ be a smooth projective geometrically connected curve over a finite field with function field $K$. Let $g$ be a connected semisimple group scheme over $X$. Under certain hypotheses we prove the equality of two numbers associated with $g$. The first is an arithmetic invariant, its Tamagawa number. The second is a geometric invariant, the number of connected components of the moduli stack of $g$-torsors on $X$. Our results are most useful for studying connected components as much is known about Tamagawa numbers.

In this paper we prove that a generalized version of the Minimal Resolution Conjecture given by Mustaţă holds for certain general sets of points on a smooth cubic surface $X\,\subset \,{{\mathbb{P}}^{3}}$. The main tool used is Gorenstein liaison theory and, more precisely, the relationship between the free resolutions of two linked schemes.

Given a positive continuous function $\mu $ on the interval $0\,<\,t\,\le \,1$, we consider the space of so-called $\mu $-Bloch functions on the unit ball. If $\mu \left( t \right)\,=\,t$, these are the classical Bloch functions. For $\mu $, we define a metric $F_{z}^{\mu }\left( u \right)$ in terms of which we give a characterization of $\mu $-Bloch functions. Then, necessary and sufficient conditions are obtained in order that a composition operator be a bounded or compact operator between these generalized Bloch spaces. Our results extend those of Zhang and Xiao.

Let $R$ be a homomorphic image of a Gorenstein local ring. Recent work has shown that there is a bridge between Auslander categories and modules of finite Gorenstein homological dimensions over $R$.

We use Gorenstein dimensions to prove new results about Auslander categories and vice versa. For example, we establish base change relations between the Auslander categories of the source and target rings of a homomorphism $\varphi :\,R\,\to \,S$ of finite flat dimension.

We produce ample (resp. NEF, eventually free) divisors in the Kontsevich space ${{\overline{\mathcal{M}}}_{\text{0,}n}}\left( {{\mathbb{P}}^{r}},d \right)$ of $n$-pointed, genus 0, stable maps to ${{\mathbb{P}}^{r}}$, given such divisors in ${{\overline{\mathcal{M}}}_{\text{0,}n+d}}$ We prove that this produces all ample (resp. NEF, eventually free) divisors in ${{\overline{\mathcal{M}}}_{\text{0,}n}}\left( {{\mathbb{P}}^{r}},\,d \right)$ As a consequence, we construct a contraction of the boundary $\,\,\mathop{\bigcup }_{k=1}^{\left\lfloor {d}/{2}\; \right\rfloor }\,{{\Delta }_{k,d-k}}$ in ${{\overline{\mathcal{M}}}_{\text{0,}0}}\left( {{\mathbb{P}}^{r}},d \right)$ analogous to a contraction of the boundary $\mathop{\bigcup }_{k=3}^{\left\lfloor {n}/{2}\; \right\rfloor }\,{{\widetilde{\Delta }}_{k,n-k}}$ in ${{\overline{\mathcal{M}}}_{\text{0,}n}}$ first constructed by Keel and McKernan.

The space now known as complete Erdős space${{\mathfrak{E}}_{\text{c}}}$ was introduced by Paul Erdős in 1940 as the closed subspace of the Hilbert space ${{\ell }^{2}}$ consisting of all vectors such that every coordinate is in the convergent sequence $\left\{ 0 \right\}\cup \left\{ 1/n:n\in \mathbb{N}\ \right\}$. In a solution to a problem posed by Lex $G$. Oversteegen we present simple and useful topological characterizations of ${{\mathfrak{E}}_{\text{c}}}$. As an application we determine the class of factors of ${{\mathfrak{E}}_{\text{c}}}$. In another application we determine precisely which of the spaces that can be constructed in the Banach spaces ${{\ell }^{p}}$ according to the ‘Erdős method’ are homeomorphic to ${{\mathfrak{E}}_{\text{c}}}$. A novel application states that if $I$ is a Polishable ${{F}_{\sigma }}$-ideal on $\omega $, then $I$ with the Polish topology is homeomorphic to either $\mathbb{Z}$, the Cantor set ${{2}^{\omega }},\,\mathbb{Z}\,\times \,{{2}^{\omega }}$, or ${{\mathfrak{E}}_{\text{c}}}$. This last result answers a question that was asked by Stevo Todorčević.

Let $p$ be a prime, and let $f:\mathbb{Z}/p\mathbb{Z}\to \mathbb{R}$ be a function with $\mathbb{E}f=0$ and $||\hat{f}|{{|}_{1}}\le 1$. Then ${{\min }_{x\in \mathbb{Z}/p\mathbb{Z}}}|f\left( x \right)|=O{{\left( \log p \right)}^{-1/3+\in }}$. One should think of $f$ as being “approximately continuous”; our result is then an “approximate intermediate value theorem”.

As an immediate consequence we show that if $A\subseteq \mathbb{Z}/p\mathbb{Z}$ is a set of cardinality $\left\lfloor {p}/{2}\; \right\rfloor $, then ${{\sum }_{r}}\widehat{|\,{{1}_{A}}}\left( r \right)|\gg {{\left( \log p \right)}^{1/3-\in }}$. This gives a result on a “$\,\bmod \,p$” analogue of Littlewood's well-known problem concerning the smallest possible ${{L}^{1}}$-norm of the Fourier transform of a set of $n$ integers.

Another application is to answer a question of Gowers. If $A\,\subseteq \,{\mathbb{Z}}/{p\mathbb{Z}}\;$ is a set of size $\left\lfloor {p}/{2}\; \right\rfloor $, then there is some $x\,\in \,\mathbb{Z}/p\mathbb{Z}$ such that

$$||A\cap \left( A+x \right)\,-\,p/4|\,=o\left( p \right).$$

Let $\Theta \,=\,\left( \alpha ,\,\beta \right)$ be a point in ${{\text{R}}^{2}}$, with $1,\,\alpha ,\,\beta $ linearly independent over $\mathrm{Q}$. We attach to $\Theta $ a quadruple $\Omega \left( \Theta \right)$ of exponents that measure the quality of approximation to $\Theta $ both by rational points and by rational lines. The two “uniform” components of $\Omega \left( \Theta \right)$ are related by an equation due to Jarník, and the four exponents satisfy two inequalities that refine Khintchine's transference principle. Conversely, we show that for any quadruple $\Omega $ fulfilling these necessary conditions, there exists a point $\Theta \,\in \,{{\text{R}}^{2}}$ for which $\Omega \left( \Theta \right)\,=\,\Omega $.

We consider the problem of determining for which square integrable functions $f$ and $g$ on the polydisk the densely defined Hankel product ${{H}_{f}}\,H_{g}^{*}$ is bounded on the Bergman space of the polydisk. Furthermore, we obtain similar results for the mixed Haplitz products ${{H}_{g}}\,{{T}_{{\bar{f}}}}$ and ${{T}_{f}}\,H_{g}^{*}$, where $f$ and $g$ are square integrable on the polydisk and $f$ is analytic.

Natural sufficient conditions for a polynomial to have a local minimum at a point are considered. These conditions tend to hold with probability 1. It is shown that polynomials satisfying these conditions at each minimum point have nice presentations in terms of sums of squares. Applications are given to optimization on a compact set and also to global optimization. In many cases, there are degree bounds for such presentations. These bounds are of theoretical interest, but they appear to be too large to be of much practical use at present. In the final section, other more concrete degree bounds are obtained which ensure at least that the feasible set of solutions is not empty.

This paper shows the existence and uniqueness of Klyachko models for irreducible unitary representations of $\text{G}{{\text{L}}_{5}}\left( \mathcal{F} \right)$, where $\mathcal{F}$ is a $p$-adic field. It is an extension of the work of Heumos and Rallis on $\text{G}{{\text{L}}_{4}}\left( \mathcal{F} \right)$.