States and Observables in Semiclassical Field Theory: a Manifestly   Covariant Approach
  A manifestly covariant formulation of quantum field Maslov complex-WKB theory (semiclassical field theory) is investigated for the case of scalar field. The main object of the theory is "semiclassical bundle". Its base is the set of all classical states, fibers are Hilbert spaces of quantum states in the external field. Semiclassical Maslov states may be viewed as points or surfaces on the semiclassical bundle. Semiclassical analogs of QFT axioms are formulated. A relationship between covariant semiclassical field theory and Hamiltonian formulation is discussed. The constructions of axiomatic field theory (Schwinger sources, Bogoliubov $S$-matrix, Lehmann-Symanzik-Zimmermann $R$-functions) are used in constructing the covariant semiclassical theory. A new covariant formulation of classical field theory and semiclassical quantization proposal are discussed. 
O.Yu.Shvedov