Theta Positivity in Lagrangian Grassmannian

We study the theta nonnegative part of Lagrangian Grassmannian. We show that it admits an orbital decomposition and is homeomorphic to a closed ball. We compare it with other positive structures. We show that it contains several totally nonnegative parts of Lagrangian Grassmannian subject to certain choices of pinnings and agrees with the nonnegativity of the generalized Plücker coordinates.