Geometric phase for non-Hermitian Hamiltonians and its holonomy interpretation

For an arbitrary possibly non-Hermitian matrix Hamiltonian H that might involve exceptional points, we construct an appropriate parameter space m and line bundle L-n over m such that the adiabatic geometric phases associated with the eigenstates of the initial Hamiltonian coincide with the holonomies of L-n. We examine the case of 2 X 2 matrix Hamiltonians in detail and show that, contrary to claims made in some recent publications, geometric phases arising from encircling exceptional points are generally geometrical and not topological in nature. (C) 2008 American Institute of Physics.