Let J and R be anti-commuting fundamental symmetries in a Hilbert space ℘. The operators J and R can be interpreted as basis (generating) elements of the complex Clifford algebra Cl2(J,R) := span{I, J;R, iJR}. An arbitrary non-trivial fundamental symmetry from Cl2(J,R) is determined by the formula [formula]. Let S be a symmetric operator that commutes with Cl2(J,R). The purpose of this paper is to study the sets [formula] of self-adjoint extensions of S in Krein spaces generated by fundamental symmetries [formula]. We show that the sets [formula] and [formula] are unitarily equivalent for different [formula] and describe in detail the structure of operators [formula] with empty resolvent set.
The paper is devoted to investigation of operators of transition and the corresponding decompositions of Krein spaces. The obtained results are applied to the study of relationship between solutions of operator Riccati equations and properties of the associated operator matrix L. In this way, we complete the known result (see Theorem 5.2 in the paper of S. Albeverio, A. Motovilov, A. Skhalikov, Integral Equ. Oper. Theory 64 (2004), 455-486) and show the equivalence between the existence of a strong solution K (//K// < 1) of the Riccati equation and similarity of the J-self-adjoint operator L to a self-adjoint one.
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