  In this talk, we examine the physical unitarity in a massive Yang-Mills
theory without the Higgs field in which the color gauge symmetry is not
spontaneously broken and kept intact. For this purpose, we use a new framework
proposed one of the authors based on a nonperturbative construction of a
non-Abelian field describing a massive spin-one vector boson field, which
enables us to perform the perturbative and nonperturbative studies on the
physical unitarity. Moreover, we present a new perturbative treatment for the
physical unitarity after giving the general properties of the massive
Yang-Mills theory. Then we reproduce the violation of physical unitarity in a
transparent way. This work is a preliminary work to the subsequent works in
which we present a nonperturbative framework to propose a possible scenario of
restoring the physical unitarity in the Curci-Ferrari model. We discuss the
implications for the low-energy QCD in relation to color confinement, glueball
mass and BRST-invariant dimension-two condensate.
