Isoparametric foliations on complex projective spaces

Abstract

Irreducible isoparametric foliations of arbitrary codimension q on complex projective spaces CP^n are classified, for (q, n) different from (1, 15). Remarkably, there are noncongruent examples that pull back under the Hopf map to congruent foliations on the sphere. Moreover, there exist many inhomogeneous isoparametric foliations, even of higher codimension. In fact, every irreducible isoparametric foliation on CP^n is homogeneous if and only if n + 1 is prime. The main tool developed in this work is a method to study singular Riemannian foliations with closed leaves on complex projective spaces. This method is based on certain graph that generalizes extended Vogan diagrams of inner symmetric spaces.