Elementary Evaluation of Convolution Sums involving the Sum of Divisors Function for a Class of positive Integers

We discuss an elementary method for the evaluation of the convolution sums $\underset{\substack{ {(l,m)\in\mathbb{N}_{0}^{2}} \\ {\alpha\,l+\beta\,m=n} } }{\sum}\sigma(l)\sigma(m)$ for those $\alpha,\beta\in\mathbb{N}$ for which $\gcd{(\alpha,\beta)}=1$ and $\alpha\beta=2^{\nu}\mho$, where $\nu\in\{0,1,2,3\}$ and $\mho$ is a finite product of distinct odd primes. Modular forms are used to achieve this result. We also generalize the extraction of the convolution sum to all natural numbers. Formulae for the number of representations of a positive integer $n$ by octonary quadratic forms using convolution sums belonging to this class are then determined when $\alpha\beta\equiv 0\pmod{4}$ or $\alpha\beta\equiv 0\pmod{3}$. To achieve this application, we first discuss a method to compute all pairs $(a,b),(c,d)\in\mathbb{N}^{2}$ necessary for the determination of such formulae for the number of representations of a positive integer $n$ by octonary quadratic forms when $\alpha\beta$ has the above form and $\alpha\beta\equiv 0\pmod{4}$ or $\alpha\beta\equiv 0\pmod{3}$. We illustrate our approach by explicitly evaluating the convolution sum for $\alpha\beta=33=3\cdot 11,\> \alpha\beta=40=2^{3}\cdot 5$ and $\alpha\beta=56=2^{3}\cdot 7$, and by revisiting the evaluation of the convolution sums for $\alpha\beta=10$, $11$, $12$, $15$, $24$. We then apply these convolution sums to determine formulae for the number of representations of a positive integer $n$ by octonary quadratic forms. In addition, we determine formulae for the number of representations of a positive integer $n$ when $(a,b)=(1,1)$, $(1,3)$, $(2,3)$, $(1,9)$.Comment: 29 pages, 8 table

Representations of simple noncommutative Jordan superalgebras I

In this article we begin the study of representations of simple finite-dimensional noncommutative Jordan superalgebras. In the case of degree $\geq 3$ we show that any finite-dimensional representation is completely reducible and, depending on the superalgebra, quasiassociative or Jordan. Then we study representations of superalgebras $D_t(\alpha,\beta,\gamma)$ and $K_3(\alpha, \beta, \gamma)$ and prove the Kronecker factorization theorem for superalgebras $D_t(\alpha,\beta,\gamma)$. In the last section we use a new approach to study noncommutative Jordan representations of simple Jordan superalgebras

Evaluation of Convolution Sums entailing mixed Divisor Functions for a Class of Levels

Let $0< n,\alpha,\beta\in\mathbb{N}$ be such that $\gcd{(\alpha,\beta)}=1$. We carry out the evaluation of the convolution sums $\underset{\substack{ {(k,l)\in\mathbb{N}^{2}} \\ {\alpha\,k+\beta\,l=n} } }{\sum}\sigma(k)\sigma_{3}(l)$ and $\underset{\substack{ {(k,l)\in\mathbb{N}^{2}} \\ {\alpha\,k+\beta\,l=n} } }{\sum}\sigma_{3}(k)\sigma(l)$ for all levels $\alpha\beta\in\mathbb{N}$, by using in particular modular forms. We next apply convolution sums belonging to this class of levels to determine formulae for the number of representations of a positive integer $n$ by the quadratic forms in twelve variables $\underset{i=1}{\overset{12}{\sum}}x_{i}^{2}$ when the level $\alpha\beta\equiv 0\pmod{4}$, and $\underset{i=1}{\overset{6}{\sum}}\,(\,x_{2i-1}^{2}+ x_{2i-1}x_{2i} + x_{2i}^{2}\,)$ when the level $\alpha\beta\equiv 0\pmod{3}$. Our approach is then illustrated by explicitly evaluating the convolution sum for $\alpha\beta=3$, $4$, $6$, $7$, $8$, $9$, $12$, $14$, $15$, $16$, $18$, $20$, $21$, $27$, $32$. These convolution sums are then applied to determine explicit formulae for the number of representations of a positive integer $n$ by quadratic forms in twelve variables.Comment: 51 pages, 9 tables. arXiv admin note: text overlap with arXiv:1609.01343, arXiv:1607.0108

The Structure Constants of the Exceptional Lie Algebra g2{\mathfrak g}_2 in the Cartan-Weyl Basis

The purpose of this paper is to answer the question whether it is possible to realize simultaneously the relations $N_{\alpha,\beta}=-N_{-\alpha,-\beta}$, $N_{\alpha,\beta}=N_{\beta,-\alpha-\beta}=N_{-\alpha-\beta,\alpha}$ and $N_{\alpha,\beta}N_{-\alpha,-\beta}=-\frac{1}{2}q(p+1)\langle\alpha,H_{\alpha}\rangle$ by the structure constants of the Lie algebra ${\mathfrak g}_2$. We show that if the structure constants obey the first relation, the three last ones are violated, and vice versa. Contrary to the second case, the first one uses the Cartan matrix elements to derive the structure constants in the form of $\langle\beta,H_{\alpha}\rangle$. The commutation relations corresponding to the first case are exactly documented in the prior literature. However, as expected, a Lie algebra isomorphism is established between the Cartan-Weyl bases obtained in both approaches.Comment: 15 pages, 2 table

Generalized (anti) Yetter-Drinfeld modules as components of a braided T-category

If H is a Hopf algebra with bijective antipode and \alpha, \beta \in Aut_{Hopf}(H), we introduce a category_H{\cal YD}^H(\alpha, \beta), generalizing both Yetter-Drinfeld and anti-Yetter-Drinfeld modules. We construct a braided T-category {\cal YD}(H) having all these categories as components, which if H is finite dimensional coincides with the representations of a certain quasitriangular T-coalgebra DT(H) that we construct. We also prove that if (\alpha, \beta) admits a so-called pair in involution, then_H{\cal YD}^H(\alpha, \beta) is isomorphic to the category of usual Yetter-Drinfeld modules_H{\cal YD}^H.Comment: 12 pages, Latex, no figure

Representation of the Gauss hypergeometric function by multiple polylogarithms and relations of multiple zeta values

We describe a solution of the Gauss hypergeometric equation, $F(\alpha,\beta,\gamma;z)$ by power series in paramaters $\alpha,\beta,\gamma$ whose coefficients are $\Z$ linear combinations of multiple polylogarithms. And using the representation and connection reletions of solutions of the hypergeometric equation, we show some relations of multiple zeta values

Grey Brownian motion local time: Existence and weak-approximation

In this paper we investigate the class of grey Brownian motions $B_{\alpha,\beta}$ ($0<\alpha<2$, $0<\beta\leq1$). We show that grey Brownian motion admits different representations in terms of certain known processes, such as fractional Brownian motion, multivariate elliptical distribution or as a subordination. The weak convergence of the increments of $B_{\alpha,\beta}$ in $t$, $w$-variables are studied. Using the Berman criterium we show that $B_{\alpha,\beta}$ admits a $\lambda$-square integrable local time $L^{B_{\alpha,\beta}}(\cdot,I)$ almost surely ($\lambda$ Lebesgue measure). Moreover, we prove that this local time can be weak-approximated by the number of crossings $C^{B_{\alpha,\beta}^{\varepsilon}}(x,I)$, of level $x$, of the convolution approximation $B_{\alpha,\beta}^{\varepsilon}$ of grey Brownian motion.Comment: 20 page

C*-algebras associated with topological group quivers II: K-groups

Topological quivers generalize the notion of directed graphs in which the sets of vertices and edges are locally compact (second countable) Hausdorff spaces. Associated to a topological quiver $Q$ is a $C^*$-correspondence, and in turn, a Cuntz-Pimsner algebra $C^*(Q).$ Given $\Gamma$ a locally compact group and $\alpha$ and $\beta$ endomorphisms on $\Gamma,$ one may construct a topological quiver $Q_{\alpha,\beta}(\Gamma)$ with vertex set $\Gamma,$ and edge set \Omega_{\alpha,\beta}(\Gamma)= \{(x,y)\in\Gamma\times\Gamma\st \alpha(y)=\beta(x)\}. In \cite{Mc1}, the author examined the Cuntz-Pimsner algebra \cO_{\alpha,\beta}(\Gamma):=C^*(Q_{\alpha,\beta}(\Gamma)) and found generators (and their relations) of \cO_{\alpha,\beta}(\Gamma). In this paper, the author uses this information to create a six term exact sequence in order to calculate the $K$-groups of \cO_{\alpha,\beta}(\Gamma).Comment: 27 page

Homomorphisms from Specht Modules to Signed Young Permutation Modules

We construct a class $\Theta_{\mathscr{R}}$ of homomorphisms from a Specht module $S_{\mathbb{Z}}^{\lambda}$ to a signed permutation module $M_{\mathbb{Z}}(\alpha|\beta)$ which generalises James's construction of homomorphisms whose codomain is a Young permutation module. We show that any $\phi \in \operatorname{Hom}_{{\mathbb{Z}}\mathfrak{S}_{n}}\big(S_{\mathbb{Z}}^\lambda, M_{\mathbb{Z}}(\alpha|\beta)\big)$ lies in the $\mathbb{Q}$-span of $\Theta_{\text{sstd}}$, a subset of $\Theta_{\mathscr{R}}$ corresponding to semistandard $\lambda$-tableaux of type $(\alpha|\beta)$. We also study the conditions for which $\Theta^{\mathbb{F}}_{\mathrm{sstd}}$ - a subset of $\operatorname{Hom}_{\mathbb{F}\mathfrak{S}_{n}}\big(S_{\mathbb{F}}^\lambda,M_{\mathbb{F}}(\alpha|\beta)\big)$ induced by $\Theta_{\mathrm{sstd}}$ - is linearly independent, and show that it is a basis for $\operatorname{Hom}_{\mathbb{F}\mathfrak{S}_{n}}\big(S_{\mathbb{F}}^\lambda,M_{\mathbb{F}}(\alpha|\beta)\big)$ when $\mathbb{F}\mathfrak{S}_{n}$ is semisimple

The structure of simple noncommutative Jordan superalgebras

In this paper we describe all subalgebras and automorphisms of simple noncommutative Jordan superalgebras $K_3(\alpha,\beta,\gamma)$ and $D_t(\alpha,\beta,\gamma)$ and compute the derivations of the nontrivial simple finite-dimensional noncommutative Jordan superalgebras