Abstract
We prove asymptotic upper bounds for the L 2 Betti numbers of the locally symmetric spaces associated with a quasi-split U(4). These manifolds are 8-dimensional, and we prove bounds in degrees 2 and 3, with the behavior in the other degrees being well understood. In degree 3, we conjecture that these bounds are sharp. Our main tool is the endoscopic classification of automorphic representations of U(N) by Mok.
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This material is based upon work supported by the National Science Foundation under Grant No. DMS-1201321 and DMS-1509331.
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Marshall, S. (2016). Endoscopy and Cohomology of a Quasi-Split U(4). In: MĂĽller, W., Shin, S., Templier, N. (eds) Families of Automorphic Forms and the Trace Formula. Simons Symposia. Springer, Cham. https://doi.org/10.1007/978-3-319-41424-9_8
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