Quantum systems with linear constraints and quadratic Hamiltonians
Quantum systems with constraints are often considered in modern theoretical physcics. All realistic field models based on the idea of gauge symmetry are of this type. A partial case of constraints being linear in coordinate and momenta operators is very important. Namely, when one applies semiclassical methods to an arbitrary constraint system, the constraints in "general position case" become linear. In the talk, different mathematicals constructions for the Hilbert space space for the constraint system are discussed. Properties of Gaussian and quasi-Gaussian wave functions for these systems are investigated. An analog of the notion of Maslov complex germ is suggested. Properties of Hamiltonians being quadratic with respect to the coordinate and momenta operators are discussed, the Green function for the evolution equation is constructed. The Maslov theorem (it says that there exists a Gaussian eigenfunction of the quantum Hamiltonian iff the classical Hamiltonian system is stable) is generalized to the constrained systems. The case of infinite number degrees of freedom (constrained Fock space) is also discussed.