EN
Let A, B be positive operators on a Hilbert space with 0 < m ≤ A, B ≤ M. Then for every unital positive linear map Φ,
Φ²((A + B)/2) ≤ K²(h)Φ²(A ♯ B),
and
Φ²((A+B)/2) ≤ K²(h)(Φ(A) ♯ Φ(B))²,
where A ♯ B is the geometric mean and K(h) = (h+1)²/(4h) with h = M/m.