In this work, we study a gauge invariant local non-polynomial composite spinor field in the fundamental representation in order to establish its renormalizability. Similar studies were already done in the case of pure Yang-Mills theories where a local composite gauge invariant vector field was obtained and an invariant renormalizable mass term could be introduced. Our model consists of a massive Euclidean Yang-Mills action with gauge group SU (N ) coupled to fermionic matter in the presence of an invariant spinor composite field and quantized in the linear covariant gauges. The whole set of Ward identities is analysed and the algebraic proof of the renormalizability of the model is obtained to all orders in a loop expansion.
I. INTRODUCTIONThe theoretical studies of quantum chromodynamics (QCD) in the low energy regime, where nonperturbative phenomena like confinement take place, still lack a satisfactory understanding.Besides quark confinement, let us underline that the gluon confinement is still a challenging, yet unsolved, issue. Several nonperturbative techniques based on the studies of the Dyson-Schwinger equations, functional renormalization group, Kugo-Ojima criterion, Gribov-Zwanziger approach and its refined version, have provided a fruitful ground for a better understanding of the behaviour of the two-point Landau gauge gluon correlation function in the infrared region, see . The output of these investigations is in quite good agreement with the lattice data on the gluon propagator, which exhibit a violation of the reflection positivity [26][27][28][29][30]. This peculiar behaviour of the gluon propagator is commonly interpreted as a signal of gluon confinement, due to the impossibility of attaching a physical meaning to the gluon as an excitation of the spectrum of the theory.