“…A U(n)-structure on a 2n-dimensional smooth manifold M is the data of a Riemannian metric g and a g-orthogonal almost complex structure J . The pair (g, J ) is also known as an almost Hermitian structure on M. When J is integrable, i.e., (M, J ) is a complex manifold, the pair (g, J ) defines a Hermitian structure on M. In this case, the metric g is called balanced when dω n−1 = 0, ω:=g (J •, •) denoting the associated fundamental form, and we shall refer to (g, J ) as a balanced U(n)-structure on M. Balanced metrics have been extensively studied in [4,[10][11][12][13]23,25] (see also the references therein).…”