Total positivity, Grassmannian and modified Bessel functions

Abstract : A rectangular matrix is called {\it totally positive} if all its minors are positive. A point of a real Grassmanian manifold $G_{l,m}$ of $l$-dimensional subspaces in $\mathbb R^m$ is called {\it strictly totally positive} if one can normalize its Pl\"ucker coordinates to make all of them positive. Clearly if a $k\times m$-matrix, $k