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arXiv · 2409.03738

Horizontal norm compatibility of cohomology classes for $\mathrm{GSp}_{6}$

Syed Waqar Ali Shah
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Abstract

We establish abstract horizontal norm relations involving the unramified Hecke-Frobenius polynomials that correspond under the Satake isomorhpism to the degree eight spinor $L$-factors of $ \mathrm{GSp}_{6} $. These relations apply to classes in the degree seven motivic cohomology of the Siegel modular sixfold obtained via Gysin pushforwards of Beilinson's Eisenstein symbol pulled back on one copy in a triple product of modular curves. The proof is based on a novel approach that circumvents the failure of the so-called multiplicity one hypothesis in our setting, which precludes the applicability of an existing technique. In a sequel, we combine our result with the previously established vertical norm relations for these classes to obtain new Euler systems for the eight dimensional Galois representations associated with certain non-endoscopic cohomological cuspidal automorphic representations of $ \mathrm{GSp}_{6} $.

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Syed Waqar Ali Shah. 2024-09-05. Horizontal norm compatibility of cohomology classes for $\mathrm{GSp}_{6}$. https://arxiv.org/abs/2409.03738

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