arXiv subjects

Adam Chapman

Publications and source records attributed to Adam Chapman.

69 records · Page 4Linked to original sources

arXiv2016

Total linkage of quaternion algebras and Pfister forms in characteristic two

We study the subfields of quaternion algebras that are quadratic extensions of their center in characteristic 2. We provide examples of the following: two non-isomorphic quaternion algebras that share all their quadratic subfields, two quaternion algebras that share all their inseparable but not all their separable quadratic subfields and two algebras that share all their separable but not all their inseparable quadratic subfields. We also discuss quaternion algebras over global fields and fields of Laurent series over a perfect field of characteristic 2 and show that the quaternion algebras over these fields are determined by their separable quadratic subfields. Throughout, these linkage questions are treated in the more general setting by considering the linkage of Pfister forms.

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arXiv2016

Standard Polynomial Equations over Division Algebras

Given a central division algebra $D$ of degree $d$ over a field $F$, we associate to any standard polynomial $ϕ(z)=z^n+c_{n-1} z^{n-1}+\dots+c_0$ over $D$ a "companion polynomial" $Φ(z)$ of degree $n d$ with coefficients in $F$ whose roots are exactly the conjugacy classes of the roots of $ϕ(z)$. We explain how in case $D$ is a quaternion algebra, all the roots of $ϕ(z)$ can be recovered from the roots of $Φ(z)$. On the way, we also generalize certain theorems that were known for $\mathbb{H}$ to any division algebra, such as the connection between the right eigenvalues of a matrix and the roots of its characteristic polynomial, and the connection between the roots of a standard polynomial and left eigenvalues of the companion matrix.

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arXiv2015

Kummer Spaces in Cyclic Algebras of Prime Degree

We classify the monomial Kummer subspaces of division cyclic algebras of prime degree $p$, showing that every such space is standard, and in particular the dimension is no greater than $p+1$. It follows that in a generic cyclic algebra, the dimension of any Kummer subspace is at most $p+1$.

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arXiv2015

Square-Central and Artin-Schreier Elements in Division Algebras

We study the behavior of square-central elements and Artin-Schreier elements in division algebras of exponent 2 and degree a power of 2. We provide chain lemmas for such elements in division algebras over 2-fields $F$ of cohomological $2$-dimension $\operatorname{cd}_2(F) \leq 2$, and deduce a common slot lemma for tensor products of quaternion algebras over such fields. We also extend to characteristic 2 a theorem proven by Merkurjev for characteristic not 2 on the decomposition of any central simple algebra of exponent 2 and degree a power of 2 over a field $F$ with $\operatorname{cd}_2(F) \leq 2$ as a tensor product of quaternion algebras.

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arXiv2015

Common subfields of p-algebras of prime degree

We show that if two division $p$-algebras of prime degree share an inseparable field extension of the center then they also share a cyclic separable one. We show that the converse is in general not true. We also point out that sharing all the inseparable field extensions of the center does not imply sharing all the cyclic separable ones.

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arXiv2015

Chain Equivalences for Symplectic Bases, Quadratic Forms and Tensor Products of Quaternion Algebras

We present a set of generators for the symplectic group which is different from the well-known set of transvections, from which the chain equivalence for quadratic forms in characteristic 2 is an immediate result. Based on the chain equivalences for quadratic forms, both in characteristic 2 and not 2, we provide chain equivalences for tensor products of quaternion algebras over fields with no nontrivial 3-fold Pfister forms. The chain equivalence for biquaternion algebras in characteristic 2 is also obtained in this process, without any assumption on the base-field.

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arXiv2014

Kummer Elements in Cyclic Algebras of Degree 5

We construct a graph of Kummer elements in a given cyclic algebra of prime degree and study its properties. In case of degree 5, we provide sufficient conditions for two elements to have a chain of Kummer elements connecting them, such that the multiplicative commutator of any two consecutive elements in the chain is a root of unity.

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arXiv2014

On the generalized Clifford algebra of a monic polynomial

In this paper we study the generalized Clifford algebra defined by Pappacena of a monic (with respect to the first variable) homogeneous polynomial $Φ(Z,X_1,\dots,X_n)=Z^d-\sum_{k=1}^d f_k(X_1,\dots,X_n) Z^{d-k}$ of degree $d$ in $n+1$ variables over some field $F$. We completely determine its structure in the following cases: $n=2$ and $d=3$ and either $\operatorname{char}(F)=3$, $f_1=0$ and $f_2(X_1,X_2)=e X_1 X_2$ for some $e \in F$, or $\operatorname{char}(F) \neq 3$, $f_1(X_1,X_2)=r X_2$ and $f_2(X_1,X_2)=e X_1 X_2+t X_2^2$ for some $r,t,e \in F$. Except for a few exceptions, this algebra is an Azumaya algebra of rank nine whose center is the coordinate ring of an affine elliptic curve. We also discuss representations of arbitrary generalized Clifford algebras assuming the base field $F$ is algebraically closed of characteristic zero.

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arXiv2014

$p$-Central Subspaces of Central Simple Algebras

We study central simple algebras in various ways, focusing on the role of $p$-central subspaces. The first part of my thesis is dedicated to the study of Clifford algebras. The standard Clifford algebra of a given form is the generic associative algebra containing a $p$-central subspace whose exponentiation form is equal to the given form. There is an old question as for whether these algebras have representations of finite rank over the center, and jointly with Daniel Krashen and Max Lieblich we managed to provide a positive answer. Different generalizations of the structure of the Clifford algebra are presented and studied in that part too. The second part is dedicated to the study of $p$-central subspaces of given central simple algebras, mainly tensor products of cyclic algebras of degree $p$. Among the results, we prove that $5$ is the upper bound for the dimension of 4-central subspaces of cyclic algebras of degree 4 containing pairs of standard generators. The third part is dedicated to chain lemmas. Chain lemmas are of importance in the theory of central simple algebras, because they form one approach to solving the word problem for the Brauer group. We prove the chain lemma for biquaternion algebras, both in characteristic 2 and characteristic not 2, and prove some partial results on the chain lemmas for cyclic algebras of degree $p$. The fourth part is dedicated to the more computational aspects of the theory. It contains results on quaternion polynomial equations and on left eigenvalues of quaternion matrices.

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arXiv2014

Quaternion quadratic equations in characteristic 2

In this paper we present a solution for any standard quaternion quadratic equation, i.e. an equation of the form $z^2+μz+ν=0$ where $μ$ and $ν$ belong to some quaternion division algebra $Q$ over some field $F$, assuming the characteristic of $F$ is $2$.

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arXiv2014

Kummer Subspaces of Tensor Products of Cyclic Algebras

We discuss the Kummer subspaces of tensor products of cyclic algebras, focusing mainly on the case of cyclic algebras of degree 3. We present a family of maximal spaces in the general case, classify all the monomial spaces in the case of tensor products of cyclic algebras of degree 3 using graph theory, and provide an upper bound for the dimension in the generic tensor product of cyclic algebras of degree 3.

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arXiv2013

Chain Lemma for Biquaternion Algebras in Characteristic 2

In this paper, we prove that for a given biquaternion algebra over a field of characteristic two, one can move from one symbol presentation to another by at most three steps, such that in each step at least one entry remains unchanged. If one requires that in each step two entries remain the same then their number increases to fifteen. We provide even more basic steps that in order to move from one symbol presentation to another one needs to use up to forty-five of them.

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arXiv2013

Pure Imaginary Roots of Quaternion Standard Polynomials

In this paper, we present a new method for solving standard quaternion equations. Using this method we reobtain the known formulas for the solution of a quadratic quaternion equation, and provide an explicit solution for the cubic quaternion equation, as long as the equation has at least one pure imaginary root. We also discuss the number of essential pure imaginary roots of a two-sided quaternion polynomial.

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arXiv2011

Clifford algebras of $p$-central sets

A generalization of the term "generalized Clifford algebras" (as appears in papers on advances in applied Clifford algebras) is introduced. This algebra is studied by means of structure theory of central simple algebras. A graph theoretical approach is proposed for studying the generating set of this algebra in case where the prime number under discussion is three. Finally, it is shown how to obtain solutions in to the equation $αY^3=αX_1^3+βX_2^3+α^2 β^2 X_3^3$ in $\mathbb{Z}[ρ]$ where $ρ$ is the primitive third root of unity.

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arXiv2011

General Polynomials over Division Algebras and Left Eigenvalues

In this paper, we present an isomorphism between the ring of general polynomials over a division ring of degree $p$ over its center $F$ and the group ring of the free monoid with $p^2$ variables. Using this isomorphism, we define the characteristic polynomial of a matrix over any division algebra, i.e. a general polynomial with one variable over the algebra whose roots are precisely the left eigenvalues. Plus, we show how the left eigenvalues of a $4 \times 4$ matrices over any division algebra can be found by solving a general polynomial equation of degree 6 over that algebra.

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