ON PROPERTIES OF DIRAC OPERATOR WITH IRREGULAR BOUNDARY CONDITIONS

The paper is concerned with the basis properties of root functions of the 2 × 2 Dirac operator with summable complex-valued potential and irregular boundary conditions. When certain conditions on the spectrum of the operator under consideration are satisfied, we prove that the system of root functions of this operator is incomplete in the space L2(0,π)⊕L2(0,π) but forms unconditional basis in the closure of its linear hull.