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A twisted topological trace formula for Hecke operators and liftings from symplectic to general linear groups
- Part of
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- Journal:
- Compositio Mathematica / Volume 148 / Issue 1 / January 2012
- Published online by Cambridge University Press:
- 09 November 2011, pp. 65-120
- Print publication:
- January 2012
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- Article
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For the locally symmetric space X attached to an arithmetic subgroup of an algebraic group G of ℚ-rank r, we construct a compact manifold
by gluing together 2r copies of the Borel–Serre compactification of X. We apply the classical Lefschetz fixed point formula to 
and get formulas for the traces of Hecke operators ℋ acting on the cohomology of X. We allow twistings of ℋ by outer automorphisms η of G. We stabilize this topological trace formula and compare it with the corresponding formula for an endoscopic group of the pair (G,η) . As an application, we deduce a weak lifting theorem for the lifting of automorphic representations from Siegel modular groups to general linear groups.
by gluing together 2
and get formulas for the traces of Hecke operators ℋ acting on the cohomology of 