  We consider the Hamiltonian and Lagrangian embedding of a first-order,
massive spin-one, gauge non-invariant theory involving anti-symmetric tensor
field. We apply the BFV-BRST generalised canonical approach to convert the
model to a first class system and construct nil-potent BFV-BRST charge and an
unitarising Hamiltonian. The canonical analysis of the St\"uckelberg
formulation of this model is presented. We bring out the contrasting feature in
the constraint structure, specifically with respect to the reducibility aspect,
of the Hamiltonian and the Lagrangian embedded model. We show that to obtain
manifestly covariant St\"uckelberg Lagrangian from the BFV embedded
Hamiltonian, phase space has to be further enlarged and show how the reducible
gauge structure emerges in the embedded model.

High Energy Physics - Theory