Pseudo-Eisenstein forms and cohomology¶of arithmetic groups. I

Let ψ be a compactly supported closed differential form on the eP] of the Borel–Serre boundary of an arithmetically defined locally symmetric space S. A closed compactly supported differential form E (ψ) on S is defined by a pseudo-Eisenstein series attached to ψ. Its degree is the degree of ψ shifted by the codimension of eP] in S. Non-vanishing results for the cohomology class E(ψ)] represented by E(ψ) are obtained by use of Poincaré duality and results on cohomology classes represented by ordinary Eisenstein series. Received: 21 July 2001 / Revised version: 17 September 2001