Donna Testerman

Publications associées (22)

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MULTIPLICITY-FREE REPRESENTATIONS OF THE PRINCIPAL A1-SUBGROUP IN A SIMPLE ALGEBRAIC GROUP

Donna Testerman

Let G be a simple algebraic group defined over an algebraically closed field k of characteristic p > 0. For p ≥ h, the Coxeter number of G, any regular unipotent element of G lies in an A1-subgroup of G; there is a unique G-conjugacy class of such subgroup ...

2025

UNICITY OF A1-SUBGROUPS ASSOCIATED TO UNIPOTENT ELEMENTS IN SIMPLE ALGEBRAIC GROUPS

Donna Testerman

Let k be an algebraically closed field of positive characteristic and G a simple algebraic group over k. Under the assumption that the characteristic is a good prime for G, we determine which unipotent elements u ∈ G, with u of order p, satisfy the propert ...

2025

Multiplicity-free Representations of Algebraic Groups

Donna Testerman, Martin W. Liebeck

Let K be an algebraically closed field of characteristic zero, and let G be a connected reductive algebraic group over K. We address the problem of classifying triples (G, H, V ), where H is a proper connected subgroup of G, and V is a finitedimensional ir ...

Amer Mathematical Soc2024

On minimal epimorphic subgroups in simple algebraic groups of rank 2

Donna Testerman

The category of linear algebraic groups admits non-surjective epimorphisms. For simple algebraic groups of rank 2 defined over algebraically closed fields, we show that the minimal dimension of a closed epimorphic subgroup is 3. ...

2023

Almost Cyclic Regular Semisimple Elements In Irreducible Representations Of Simple Algebraic Groups

Donna Testerman

Let G be a simple linear algebraic group defined over an algebraically closed field of characteristic p >= 0 and let phi be a nontrivial p-restricted irreducible representation of G. Let T be a maximal torus of G and s epsilon T. We say that s is Ad-regula ...

2023

Multiplicity-free representations of algebraic groups II

Donna Testerman, Martin W. Liebeck

We continue our work, started in [9], on the program of classifying triples (X, Y, V), where X, Yare simple algebraic groups over an algebraically closed field of characteristic zero with X < Y, and Vis an irreducible module for Y such that the restriction ...

ACADEMIC PRESS INC ELSEVIER SCIENCE2022

Spectra of non-regular elements in irreducible representations of simple algebraic groups

Donna Testerman

We study the spectra of non-regular semisimple elements in irreducible representations of simple algebraic groups. More precisely, we prove that if G is a simply connected simple linear algebraic group and φ : G → GL(V ) is a non-trivial irreducible repres ...

2021

A new family of irreducible subgroups of the orthogonal algebraic groups

Donna Testerman, Mikaël Cavallin

American Mathematical Society (AMS)2019

Minimal Polynomials Of Unipotent Elements Of Non-Prime Order In Irreducible Representations Of The Exceptional Algebraic Groups In Some Good Characteristics

Donna Testerman

In a number of cases the minimal polynomials of the images of unipotent elements of non-prime order in irreducible representations of the exceptional algebraic groups in good characteristics are found. It is proved that if p > 5 for a group of type E-8 and ...

2019

$A_1$-type subgroups containing regular unipotent elements

Donna Testerman

Let be a simple exceptional algebraic group of adjoint type over an algebraically closed field of characteristic and let be a subgroup of containing a regular unipotent element of . By a theorem of Testerman, is contained in a connected subgroup of of type ...

2019

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Minimal Polynomials Of Unipotent Elements Of Non-Prime Order In Irreducible Representations Of The Exceptional Algebraic Groups In Some Good Characteristics

Donna Testerman

2019

$A_1$-type subgroups containing regular unipotent elements

Donna Testerman

2019

A new family of irreducible subgroups of the orthogonal algebraic groups

Donna Testerman, Mikaël Cavallin

American Mathematical Society (AMS)2019