The S-functional calculus for the Clifford adjoint operator

In this paper, we work within the framework of modules over the Clifford algebra Rd. Our investigation focuses on the S-spectrum and the S-functional calculus in its various forms for the adjoint T* of a Clifford operator T. One of the key results we present is that the bisectoriality of T can be transferred to T*. This is grounded in the fact that, for Clifford operators, the S-spectrum of the adjoint operator T* is identical to that of T. Furthermore, we demonstrate that for the existing formulations of the S-functional calculus, including bounded, unbounded, $ω$, and H^∞ versions, there is a clear connection between the left functional calculus of T and the right functional calculus of T*. This explicit link between the left functional calculus of T and the right functional calculus of T* and vice versa is obtained using the function f^#(s):=f(s̄). Finally, we discuss the fact that the S-spectrum, related to the invertibility of the second-order operator T^2-2s_0T+|s|^2, can actually be characterized through the invertibility of the first-order R-linear operator T-I^Rs.