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Search: MSC category 14L ( Algebraic groups {For linear algebraic groups, see 20Gxx; for Lie algebras, see 17B45} )

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1. CMB 2012 (vol 57 pp. 303)

Gille, Philippe
Octonion Algebras over Rings are not Determined by their Norms
Answering a question of H. Petersson, we provide a class of examples of pair of octonion algebras over a ring having isometric norms.

Keywords:octonion algebras, torsors, descent
Categories:14L24, 20G41

2. CMB 2012 (vol 57 pp. 97)

Levy, Jason
Rationality and the Jordan-Gatti-Viniberghi decomposition
We verify our earlier conjecture and use it to prove that the semisimple parts of the rational Jordan-Kac-Vinberg decompositions of a rational vector all lie in a single rational orbit.

Keywords:reductive group, $G$-module, Jordan decomposition, orbit closure, rationality
Categories:20G15, 14L24

3. CMB 2006 (vol 49 pp. 592)

Sarti, Alessandra
Group Actions, Cyclic Coverings and Families of K3-Surfaces
In this paper we describe six pencils of $K3$-surfaces which have large Picard number ($\rho=19,20$) and each contains precisely five special fibers: four have A-D-E singularities and one is non-reduced. In particular, we characterize these surfaces as cyclic coverings of some $K3$-surfaces described in a recent paper by Barth and the author. In many cases, using 3-divisible sets, resp., 2-divisible sets, of rational curves and lattice theory, we describe explicitly the Picard lattices.

Categories:14J28, 14L30, 14E20, 14C22

4. CMB 2004 (vol 47 pp. 22)

Goto, Yasuhiro
A Note on the Height of the Formal Brauer Group of a $K3$ Surface
Using weighted Delsarte surfaces, we give examples of $K3$ surfaces in positive characteristic whose formal Brauer groups have height equal to $5$, $8$ or $9$. These are among the four values of the height left open in the article of Yui \cite{Y}.

Keywords:formal Brauer groups, $K3$ surfaces in positive, characteristic, weighted Delsarte surfaces
Categories:14L05, 14J28

5. CMB 2003 (vol 46 pp. 204)

Levy, Jason
Rationality and Orbit Closures
Suppose we are given a finite-dimensional vector space $V$ equipped with an $F$-rational action of a linearly algebraic group $G$, with $F$ a characteristic zero field. We conjecture the following: to each vector $v\in V(F)$ there corresponds a canonical $G(F)$-orbit of semisimple vectors of $V$. In the case of the adjoint action, this orbit is the $G(F)$-orbit of the semisimple part of $v$, so this conjecture can be considered a generalization of the Jordan decomposition. We prove some cases of the conjecture.

Categories:14L24, 20G15

6. CMB 2003 (vol 46 pp. 140)

Renner, Lex E.
An Explicit Cell Decomposition of the Wonderful Compactification of a Semisimple Algebraic Group
We determine an explicit cell decomposition of the wonderful compactification of a semi\-simple algebraic group. To do this we first identify the $B\times B$-orbits using the generalized Bruhat decomposition of a reductive monoid. From there we show how each cell is made up from $B\times B$-orbits.

Categories:14L30, 14M17, 20M17

7. CMB 2002 (vol 45 pp. 686)

Rauschning, Jan; Slodowy, Peter
An Aspect of Icosahedral Symmetry
We embed the moduli space $Q$ of 5 points on the projective line $S_5$-equivariantly into $\mathbb{P} (V)$, where $V$ is the 6-dimensional irreducible module of the symmetric group $S_5$. This module splits with respect to the icosahedral group $A_5$ into the two standard 3-dimensional representations. The resulting linear projections of $Q$ relate the action of $A_5$ on $Q$ to those on the regular icosahedron.

Categories:14L24, 20B25

8. CMB 2001 (vol 44 pp. 491)

Wang, Weiqiang
Resolution of Singularities of Null Cones
We give canonical resolutions of singularities of several cone varieties arising from invariant theory. We establish a connection between our resolutions and resolutions of singularities of closure of conjugacy classes in classical Lie algebras.

Categories:14L35, 22G

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