We study groups definable in tame expansions of ω-stable theories. Assuming several tameness conditions, we obtain structural theorems for groups definable and interpretable in these expansions. As our main example, by characterizing independence in the pair, where K is an algebraically closed field and G is a multiplicative subgroup of K× with the Mann property, we show that the pair satisfies the assumptions. In particular, this provides a characterization of definable and interpretable groups in in terms of algebraic groups in (...) K and interpretable groups in G. Furthermore, we compute the Morley rank and the U-rank in and both ranks agree. (shrink)

In this paper, we study an algebraically closed field \ expanded by two unary predicates denoting an algebraically closed proper subfield k and a multiplicative subgroup \. This will be a proper expansion of algebraically closed field with a group satisfying the Mann property, and also pairs of algebraically closed fields. We first characterize the independence in the triple \\). This enables us to characterize the interpretable groups when \ is divisible. Every interpretable group H in \\) is, up to (...) isogeny, an extension of a direct sum of k-rational points of an algebraic group defined over k and an interpretable abelian group in \ by an interpretable group N, which is the quotient of an algebraic group by a subgroup \, which in turn is isogenous to a cartesian product of k-rational points of an algebraic group defined over k and an interpretable abelian group in \. (shrink)