Local exponents and infinitesimal generators of canonical transformations on Boson Fock spaces

Abstract

A one-parameter symplectic group $\{e^{t\dA}\}_{t\in\RR}$ derives proper canonical transformations on a Boson Fock space. It has been known that the unitary operator $U_t$ implementing such a proper canonical transformation gives a projective unitary representation of $\{e^{t\dA}\}_{t\in\RR}$ and that $U_t$ can be expressed as a normal-ordered form. We rigorously derive the self-adjoint operator $\D(\dA)$ and a phase factor $e^{i\int_0^t\TA(s)ds}$ with a real-valued function $\TA$ such that $U_t=e^{i\int_0^t\TA(s)ds}e^{it\D(\dA)}$. Key words: Canonical transformations(Bogoliubov transformations), symplectic groups, projective unitary representations, one-parameter unitary groups, infinitesimal self-adjoint generators, local factors, local exponents, normal-ordered quadratic expressions.