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arXiv 2404.18554math.AG
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概形上的三元性

Triality over Schemes

Cameron Ruether

AI总结:

本文在任意基概形上利用秩8分裂双曲二次型的克利福德代数与D4型群的Chevalley生成元,绕开八元数代数重新发展三元性,构造三元三元组和三元代数的栈,并证明其分别等价于PGO₈⁺-torsors及PGO₈⁺⋊S₃-torsors的gerbe。

摘要:

在任意基概形上,我们提供了一种三元性的替代发展路径,该路径不使用八元数代数或对称合成代数。取而代之的是,我们使用秩为8的分裂双曲二次型的克利福德代数,并利用类型为$D_4$的群的Chevalley生成元进行计算。遵循《对合之书》[KMRT]的策略,我们随后定义了三元三元组的栈,并证明它等价于$\mathbf{PGO}_8^+$--torsors的gerbe。我们证明它具有生成同构于$\mathbb{S}_3$的群的自同态,并且$\mathbf{PGO}_8^+$的几个熟悉的同调性质在此设定下作为结果成立。接下来,我们定义了三元代数的栈,并证明它等价于$\mathbf{PGO}_8^+\rtimes \mathbb{S}_3$--torsors的gerbe。因此,它也等价于类型为$D_4$的单连通群和伴随群的gerbe。我们为三元代数定义了$\mathbf{Spin}_\mathcal{T}$和$\mathbf{PGO}^+_\mathcal{T}$,并定义了具体的函子$\mathcal{T} \mapsto \mathbf{Spin}_\mathcal{T}$和$\mathcal{T} \mapsto \mathbf{PGO}^+_\mathcal{T}$来实现这些等价性。

英文摘要:

Working over an arbitrary base scheme, we provide an alternative development of triality which does not use Octonion algebras or symmetric composition algebras. Instead, we use the Clifford algebra of the split hyperbolic quadratic form of rank 8 and computations with Chevalley generators of groups of type $D_4$. Following the strategy of The Book of Involutions [KMRT], we then define the stack of trialitarian triples and show it is equivalent to the gerbe of $\mathbf{PGO}_8^+$--torsors. We show it has endomorphisms generating a group isomorphic to $\mathbb{S}_3$ and that several familiar cohomological properties of $\mathbf{PGO}_8^+$ follow in this setting as a result. Next, we define the stack of trialitarian algebras and show it is equivalent to the gerbe of $\mathbf{PGO}_8^+\rtimes \mathbb{S}_3$--torsors. Because of this, it is also equivalent to the gerbes of simply connected, respectively adjoint, groups of type $D_4$. We define $\mathbf{Spin}_\mathcal{T}$ and $\mathbf{PGO}^+_\mathcal{T}$ for a trialitarian algebra and define concrete functors $\mathcal{T} \mapsto \mathbf{Spin}_\mathcal{T}$ and $\mathcal{T} \mapsto \mathbf{PGO}^+_\mathcal{T}$ which realize these equivalences.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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