2022

Convolution in Dual Cesàro Sequence Spaces

Curbera, Guillermo P. — Fri, 16 Dec 2022 00:00:00 GMT

Convolution in Dual Cesàro Sequence Spaces Curbera, Guillermo P.; Ricker, Werner J. We investigate convolution operators in the sequence spaces $d_p$, for 1 $\leqslant p<\infty$. These spaces, for $p$ > 1, arise as dual spaces of the Cesàro sequence spaces $ces_p$ thoroughly investigated by G. Bennett. A detailed study is also made of the algebra of those sequences which convolve $d_p$ into $d_p$. It turns out that such multiplier spaces exhibit features which are very different to the classical multiplier spaces of $l^{p}$.

Hutchinson's Intervals and Entire Functions from the Laguerre-Pólya Class

Nguyen, Thu Hien — Mon, 12 Dec 2022 00:00:00 GMT

Hutchinson's Intervals and Entire Functions from the Laguerre-Pólya Class Nguyen, Thu Hien; Vishnyakova, Anna We find the intervals $[\alpha, \beta (\alpha)]$ such that if a univariate real polynomial or entire function $f(z) = a_0 + a_1 z + a_2 z^2 + \cdots $ with positive coefficients satisfy the conditions $ \frac{a_{k-1}^2}{a_{k-2}a_{k}} \in [\alpha, \beta(\alpha)]$ for all $k \geq 2,$ then $f$ belongs to the Laguerre-Pólya class. For instance, from J.I. Hutchinson's theorem, one can observe that $f$ belongs to the Laguerre-Pólya class (has only real zeros) when $q_k(f) \in [4, + \infty).$ We are interested in finding those intervals which are not subsets of $[4, + \infty).$

Quasi-Equilibria and Click Times for a Variant of Muller's Ratchet

González Casanova, Adrian — Wed, 30 Nov 2022 00:00:00 GMT

Quasi-Equilibria and Click Times for a Variant of Muller's Ratchet González Casanova, Adrian; Smadi, Charline; Wakolbinger, Anton Consider a population of $N$ individuals, each of them carrying a type in $\mathbb N_0$. The population evolves according to a Moran dynamics with selection and mutation, where an individual of type $k$ has the same selective advantage over all individuals with type $k' > k$, and type $k$ mutates to type $k+1$ at a constant rate. This model is thus a variation of the classical Muller's ratchet: there the selective advantage is proportional to $k' - k$. For a regime of selection strength and mutation rates which is between the regimes of weak and strong selection/mutation, we obtain the asymptotic rate of the click times of the ratchet (i.e. the times at which the hitherto minimal ('best') type in the population is lost), and reveal the quasi-stationary type frequency profile between clicks. The large population limit of this profile is characterized as the normalized attractor of a "dual" hierarchical multitype logistic system, and also via the distribution of the final minimal displacement in a branching random walk with one-sided steps. An important role in the proofs is played by a graphical representation of the model, both forward and backward in time, and a central tool is the ancestral selection graph decorated by mutations.

Birational Rowmotion on a Rectangle over a Noncommutative Ring

Grinberg, Darij — Tue, 20 Sep 2022 00:00:00 GMT

Birational Rowmotion on a Rectangle over a Noncommutative Ring Grinberg, Darij; Roby, Tom We extend the periodicity of birational rowmotion for rectangular posets to the case when the base field is replaced by a noncommutative ring (under appropriate conditions). This resolves a conjecture from 2014. The proof uses a novel approach and is fully self-contained.

Root Cycles in Coxeter Groups

Hart, Sarah — Thu, 15 Sep 2022 00:00:00 GMT

Root Cycles in Coxeter Groups Hart, Sarah; Kelsey, Veronica; Rowley, Peter For an element $w$ of a Coxeter group $W$ there are two important attributes, namely its length, and its expression as a product of disjoint cycles in its action on $\Phi$, the root system of $W$. This paper investigates the interaction between these two features of $w$, introducing the notion of the crossing number of $w$, $\kappa(w)$. Writing $w = c_1 \cdots c_r$ as a product of disjoint cycles we associate to each cycle $c_i$ a `crossing number' $\kappa(c_i)$, which is the number of positive roots $\alpha$ in $c_i$ for which $w\cdot \alpha$ is negative. Let Seq$_k(w)$ be the sequence of $\kappa(c_i)$ written in increasing order, and let $\kappa(w)$ = max Seq$_k(w)$. The length of $w$ can be retrieved from this sequence, but Seq$_k(w)$ provides much more information. For a conjugacy class $X$ of $W$ let $k_{\min}(X)=\min \{\kappa(w) \;|\;w \in X\}$ and let $\kappa(W)$ be the maximum value of $k_{\min}$ across all conjugacy classes of $W$. We call $\kappa(w)$ and $\kappa(W)$, respectively, the crossing numbers of $w$ and $W$. Here we determine the crossing numbers of all finite Coxeter groups and of all universal Coxeter groups. We also show, among other things, that for finite irreducible Coxeter groups if $u$ and $v$ are two elements of minimal length in the same conjugacy class $X$, then Seq$_k(u)$ = Seq$_k(v)$ and $k_{\min}(X)=\kappa(u)=\kappa(v)$. Also it is shown that the crossing number of an arbitrary Coxeter group is bounded below by the crossing number of a standard parabolic subgroup. Finally, examples are given to show that crossing numbers can be arbitrarily large for finite and infinite irreducible Coxeter groups.

Convergence and Error Analysis of Compressible Fluid Flows with Random Data: Monte Carlo Method

Feireisl, Eduard — Thu, 25 Aug 2022 00:00:00 GMT

Convergence and Error Analysis of Compressible Fluid Flows with Random Data: Monte Carlo Method Feireisl, Eduard; Lukáčova-Medviďová, Mariá; She, Bangwei; Yuan, Yuhuan The goal of this paper is to study convergence and error estimates of the Monte Carlo method for the Navier-Stokes equations with random data. To discretize in space and time, the Monte Carlo method is combined with a suitable deterministic discretization scheme, such as a fnite volume method. We assume that the initial data, force and the viscosity coefficients are random variables and study both, the statistical convergence rates as well as the approximation errors. Since the compressible Navier-Stokes equations are not known to be uniquely solvable in the class of global weak solutions, we cannot apply pathwise arguments to analyze the random Navier-Stokes equations. Instead we have to apply intrinsic stochastic compactness arguments via the Skorokhod representation theorem and the Gyöngy-Krylov method. Assuming that the numerical solutions are bounded in probability, we prove that the Monte Carlo fnite volume method converges to a statistical strong solution. The convergence rates are discussed as well. Numerical experiments illustrate theoretical results.

On a Conjecture of Khoroshkin and Tolstoy

Appel, Andrea — Tue, 02 Aug 2022 00:00:00 GMT

On a Conjecture of Khoroshkin and Tolstoy Appel, Andrea; Gautam, Sachin; Wendlandt, Curtis We prove a no-go theorem on the factorization of the lower triangular part in the Gaussian decomposition of the Yangian's universal $R$-matrix, yielding a negative answer to a conjecture of Khoroshkin and Tolstoy from [Lett. Math. Phys. vol. 36 1996].

Embedding Spaces of Split Links

Boyd, Rachael — Mon, 01 Aug 2022 00:00:00 GMT

Embedding Spaces of Split Links Boyd, Rachael; Bregman, Corey We study the homotopy type of the space $\mathcal{E}(L)$ of unparametrised embeddings of a split link $L=L_1\sqcup \ldots \sqcup L_n$ in $\mathbb{R}^3$. Inspired by work of Brendle and Hatcher, we introduce a semi-simplicial space of separating systems and show that this is homotopy equivalent to $\mathcal{E}(L)$. This combinatorial object provides a gateway to studying the homotopy type of $\mathcal{E}(L)$ via the homotopy type of the spaces $\mathcal{E}(L_i)$. We apply this tool to find a simple description of the fundamental group, or motion group, of $\mathcal{E}(L)$, and extend this to a description of the motion group of embeddings in $S^3$.

Shock-avoiding Slicing Conditions: Tests and Calibrations

Baumgarte, Thomas W. — Tue, 19 Jul 2022 00:00:00 GMT

Shock-avoiding Slicing Conditions: Tests and Calibrations Baumgarte, Thomas W.; Hilditch, David While the 1+log slicing condition has been extremely successful in numerous numerical relativity simulations, it is also known to develop "gauge-shocks" in some examples. Alternative "shockavoiding" slicing conditions suggested by Alcubierre prevent these pathologies in those examples, but have not yet been explored and tested very broadly. In this paper we compare the performance of shock-avoiding slicing conditions with those of 1+log slicing for a number of "text-book" problems, including black holes and relativistic stars. While, in some simulations, the shock-avoiding slicing conditions feature some unusual properties and lead to more "gauge-dynamics" than the 1+log slicing condition, we find that they perform quite similarly in terms of stability and accuracy, and hence provide a very viable alternative to 1+log slicing.

On the Enumeration of Finite $L$-Algebras

Dietzel, Carsten — Wed, 29 Jun 2022 00:00:00 GMT

On the Enumeration of Finite $L$-Algebras Dietzel, Carsten; Menchón, Paula; Vendramin, Leandro We use Constraint Satisfaction Methods to construct and enumerate finite L-algebras up to isomorphism. These objects were recently introduced by Rump and appear in Garside theory, algebraic logic, and the study of the combinatorial Yang-Baxter equation. There are 377322225 isomorphism classes of $L$-algebras of size eight. The database constructed suggest the existence of bijections between certain classes of $L$-algebras and well-known combinatorial objects. On the one hand, we prove that Bell numbers enumerate isomorphism classes of finite linear $L$-algebras. On the other hand, we also prove that finite regular $L$-algebras are in bijective correspondence with infinite-dimensional Young diagrams.