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.
@article{bwmeta1.element.bwnjournal-article-doi-10_4064-sm215-2-6, author = {Minghua Lin}, title = {Squaring a reverse AM-GM inequality}, journal = {Studia Mathematica}, volume = {215}, year = {2013}, pages = {187-194}, zbl = {1276.47022}, language = {en}, url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-sm215-2-6} }
Minghua Lin. Squaring a reverse AM-GM inequality. Studia Mathematica, Tome 215 (2013) pp. 187-194. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-sm215-2-6/