arXiv subjects

Sophie Morier-Genoud

Publications and source records attributed to Sophie Morier-Genoud.

35 records · Page 2Linked to original sources

arXiv2013

Classification of the algebras $\mathbb{O}_{p,q}$

We study a series of real nonassociative algebras $\mathbb{O}_{p,q}$ introduced in $[5]$. These algebras have a natural $\mathbb{Z}_2^n$-grading, where $n=p+q$, and they are characterized by a cubic form over the field $\mathbb{Z}_2$. We establish all the possible isomorphisms between the algebras $\mathbb{O}_{p,q}$ preserving the structure of $\mathbb{Z}_2^n$-graded algebra. The classification table of $\mathbb{O}_{p,q}$ is quite similar to that of the real Clifford algebras $\mathrm{Cl}_{p,q}$, the main difference is that the algebras $\mathbb{O}_{n,0}$ and $\mathbb{O}_{0,n}$ are exceptional.

math.AC↗

arXiv2013

A short survey of Lie antialgebras

This article is the writing notes of a talk on Lie Antialgebras given by the second author at the conference "3Quantum: Algebra Geometry Information" that held in Tallinn in July 2012. The aim of this note is to give a brief survey of the existing theory of Lie antialgebras and to suggest open questions.

math-ph↗

arXiv2013

Linear difference equations, frieze patterns and combinatorial Gale transform

We study the space of linear difference equations with periodic coefficients and (anti)periodic solutions. We show that this space is isomorphic to the space of tame frieze patterns and closely related to the moduli space of configurations of points in the projective space. We define the notion of combinatorial Gale transform which is a duality between periodic difference equations of different orders. We describe periodic rational maps generalizing the classical Gauss map.

math.CO↗

arXiv2012

Orthogonal Designs and a Cubic Binary Function

Orthogonal designs are fundamental mathematical notions used in the construction of space time block codes for wireless transmissions. Designs have two important parameters, the rate and the decoding delay; the main problem of the theory is to construct designs maximizing the rate and minimizing the decoding delay. All known constructions of CODs are inductive or algorithmic. In this paper, we present an explicit construction of optimal CODs. We do not apply recurrent procedures and do calculate the matrix elements directly. Our formula is based on a cubic function in two binary n-vectors. In our previous work (Comm. Math. Phys., 2010, and J. Pure and Appl. Algebra, 2011), we used this function to define a series of non-associative algebras generalizing the classical algebra of octonions and to obtain sum of squares identities of Hurwitz-Radon type.

cs.IT↗

arXiv2012

Arithmetics of 2-friezes

We consider the variant of Coxeter-Conway frieze patterns called 2-frieze. We prove that there exist infinitely many closed integral 2-friezes (i.e. containing only positive integers) provided the width of the array is bigger than 4. We introduce operations on the integral 2-friezes generating bigger or smaller closed integral 2-friezes.

math.CO↗

arXiv2011

2-frieze patterns and the cluster structure of the space of polygons

We study the space of 2-frieze patterns generalizing that of the classical Coxeter-Conway frieze patterns. The geometric realization of this space is the space of n-gons (in the projective plane and in 3-dimensional vector space) which is a close relative of the moduli space of genus 0 curves with n marked points. We show that the space of 2-frieze patterns is a cluster manifold and study its algebraic and arithmetic properties.

math.AG↗

arXiv2011

Superalgebras associated to Riemann surfaces: Jordan algebras of Krichever-Novikov type

We construct two superalgebras associated to a punctured Riemann surface. One of them is a Lie superalgebra of Krichever-Novikov type, the other one is a Jordan superalgebra. The constructed algebras are related in several ways (algebraic, geometric, representation theoretic). In particular, the Lie superalgebra is the algebra of derivations of the Jordan superalgebra.

math.RA↗

arXiv2011

New solutions to the Hurwitz problem on square identities

The Hurwitz problem of composition of quadratic forms, or of "sum of squares identity" is tackled with the help of a particular class of $(\mathbb{Z}_2)^n$-graded non-associative algebras generalizing the octonions. This method provides an explicit formula for the classical Hurwitz-Radon identity and leads to new solutions in a neighborhood of the Hurwitz-Radon identity.

math.AC↗

arXiv2011

A series of algebras generalizing the octonions and Hurwitz-Radon identity

We study non-associative twisted group algebras over $(\Z_2)^n$ with cubic twisting functions. We construct a series of algebras that extend the classical algebra of octonions in the same way as the Clifford algebras extend the algebra of quaternions. We study their properties, give several equivalent definitions and prove their uniqueness within some natural assumptions. We then prove a simplicity criterion. We present two applications of the constructed algebras and the developed technique. The first application is a simple explicit formula for the following famous square identity: $(a_1^2+...+a_{N}^2)\,(b_1^2+...+b_{ρ(N)}^2)= c_1^2+...+c_{N}^2$, where $c_k$ are bilinear functions of the $a_i$ and $b_j$ and where $ρ(n)$ is the Hurwitz-Radon function. The second application is the relation to Moufang loops and, in particular, to the code loops. To illustrate this relation, we provide an explicit coordinate formula for the factor set of the Parker loop.

math.RA↗

arXiv2010

Universal Enveloping Algebras of Lie Antialgebras

Lie antialgebras is a class of supercommutative algebras recently appeared in symplectic geometry. We define the notion of enveloping algebra of a Lie antialgebra and study its properties. We show that every Lie antialgebra is canonically related to a Lie superalgebra and prove that its enveloping algebra is a quotient of the enveloping algebra of the corresponding Lie superalgebra.

math.AC↗

arXiv2009

Graded commutative algebras: examples, classification, open problems

We consider $\G$-graded commutative algebras, where $\G$ is an abelian group. Starting from a remarkable example of the classical algebra of quaternions and, more generally, an arbitrary Clifford algebra, we develop a general viewpoint on the subject. We then give a recent classification result and formulate an open problem.

math-ph↗

arXiv2009

Simple graded commutative algebras

We study the notion of $Γ$-graded commutative algebra for an arbitrary abelian group $Γ$. The main examples are the Clifford algebras already treated by Albuquerque and Majid. We prove that the Clifford algebras are the only simple finite-dimensional associative graded commutative algebras over $\mathbb{R}$ or $\mathbb{C}$. Our approach also leads to non-associative graded commutative algebras extending the Clifford algebras.

math.AC↗

arXiv2008

Well, Papa, can you multiply triplets?

We show that the classical algebra of quaternions is a commutative $\Z_2\times\Z_2\times\Z_2$-graded algebra. A similar interpretation of the algebra of octonions is impossible.

math.AC↗

arXiv2008

Representations of $asl_2$

We study representations of the simple Lie antialgebra $asl_2$ introduced by Ovsienko. We show that representations of $asl_2$ are closely related to the famous ghost Casimir element of the universal enveloping algebra $osp(1|2)$. We prove that $asl_2$ has no non-trivial finite-dimensional representations; we define and classify some particular infinite-dimensional representations that we call weighted representations.

math.RT↗

arXiv2005

Geometric lifting of the canonical basis and semitoric degenerations of Richardson varieties

In the sl\_n case, A. Berenstein and A. Zelevinsky studied the Schützenberger involution in terms of Lusztig's canonical basis, [3]. We generalize their construction and formulas for any semisimple Lie algebra. We use for this the geometric lifting of the canonical basis, on which an analogue of the Schützenberger involution can be given. As an application, we construct semitoric degenerations of Richardson varieties, following a method of P. Caldero, [6]

math.RT↗

arXiv2003

Realisation of Lusztig cones

The negative part $U^-$ of a quantised enveloping algebra associated to a simple Lie algebra possesses a canonical basis $\mathcal{B}$ with favourable properties. Lusztig has associated a cone to a reduced expression $\mathbf{i}$ for the longest element $w_0$ in the Weyl group of $\mathfrak{g}$, with good properties with respect to monomial elements of $\mathcal{B}$. The first author has associated a subalgebra $A_{\mathbf{i}}$ of $U^-$, compatible with the dual basis $\mathcal{B}^*$, to each reduced expression $\mathbf{i}$. We show that, after a certain twisting, the string parametrisation of the adapted basis of this subalgebra coincides with the corresponding Lusztig cone. As an application, we give explicit expressions for the generators of the Lusztig cones.

math.RT↗

arXiv2003

Relevement geometrique de la base canonique et involution de Schützenberger

Let $G$ be a complex simply connected semisimple Lie group, and let $B_V$ be the canonical base of a Weyl module $V$ of $G$. We calculate explicitely the action of the longest element $w_0$ of the Weyl group on $B_V$ in terms of parametrizations. The method is based on results of Berenstein and Zelevinsky on the geometric lifting.

math.RT↗