Elementary rotations of operators in regular Banach spaces

In this paper we prove the existence of an elementary rotation (a Julia operator) for any continuous linear adjointable operator in a regular Banach space with inner product. The proof is based on a more general theorem of the same author about the existence of an elementary rotation for any linear operator in a category with quadratic splitting. This result is a generalization of a well-known result about the existence of an elementary rotation for any continuous linear operator in a Krein space. The result can be useful for constructing isometric and unitary dilations as well as characteristic functions of continuous linear operators acting in regular Banach spaces with inner product.