The cohomology of an arithmetic subgroup of a connected reductive algebraic group defined over can be interpreted in terms of the automorphic spectrum of . In this frame there is a sum decomposition of the cohomology into the cuspidal cohomology ( i.e., classes represented by cuspidal automorphic forms for ) and the so called Eisenstein cohomology. The present paper deals with the case of a quasi split form of -rank two of a unitary group of degree four. We describe in detail the Eisenstein series which give rise to non-trivial cohomology classes and the cuspidal automorphic forms for the Levi components of parabolic -subgroups to which these classes are attached. Mainly the generic case will be treated, i.e., we essentially suppose that the coefficient system is regular.
"On arithmetic subgroups of a Q-rank 2 form of SU(2,2) and their automorphic cohomology." J. Math. Soc. Japan 57 (2) 357 - 385, April, 2005. https://doi.org/10.2969/jmsj/1158242063