Extensions of Lieb's concavity theorem

The operator function (A,B)→ Trf(A,B)(K *)K, defined in pairs of bounded self-adjoint operators in the domain of a function f of two real variables, is convex for every Hilbert Schmidt operator K, if and only if f is operator convex. We obtain, as a special case, a new proof of Lieb's concavity theorem for the function (A,B)→ TrA ^p K* B ^q K, where p and q are non-negative numbers with sum p+q ≤ 1. In addition, we prove concavity of the operator function (A,B) → Tr [ A/A+μ ₁K*B/B+μ₂K] in its natural domain D ₂(μ₁,μ₂), cf. Definition 3.