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arXiv · 1805.09373

On the cohomology of congruence subgroups of GL3 over the Eisenstein integers

Paul E. Gunnells·Mark McConnell·Dan Yasaki
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Abstract

Let F be the imaginary quadratic field of discriminant -3 and OF its ring of integers. Let Gamma be the arithmetic group GL_3 (OF), and for any ideal n subset OF let Gamma_0 (n) be the congruence subgroup of level n consisting of matrices with bottom row (0,0,*) bmod n. In this paper we compute the cohomology spaces H^{nu - 1} (Gamma_0 (n); C) as a Hecke module for various levels n, where nu is the virtual cohomological dimension of Gamma. This represents the first attempt at such computations for GL_3 over an imaginary quadratic field, and complements work of Grunewald--Helling--Mennicke and Cremona, who computed the cohomology of GL_2 over imaginary quadratic fields. In our results we observe a variety of phenomena, including cohomology classes that apparently correspond to nonselfdual cuspforms on GL_3/F.

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Paul E. Gunnells, Mark McConnell, Dan Yasaki. 2018-05-23. On the cohomology of congruence subgroups of GL3 over the Eisenstein integers. https://arxiv.org/abs/1805.09373

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