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Published online by Cambridge University Press: 24 October 2008
We introduce a rational-valued invariant which is capable of distinguishing between the commensurability classes of certain discrete groups, namely, the fundamental groups of smooth closed orientable aspherical manifolds of dimensional 4k(k ≥ 1) whose Euler characteristic χ(Λ) is non-zero. The invariant in question is the quotient
where Sign (Λ) is the absolute value of the signature of the intersection form
and [Λ] is a generator of H4k(Λ; ℝ).