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We derive general covariant coupled equations of QCD describing the tetraquark in terms of a mix of four-quark states $2q2bar q$, and two-quark states $qbar q$. The coupling of $2q2bar q$ to $qbar q$ states is achieved by a simple contraction of a four-quark $qbar q$-irreducible Green function down to a two-quark $qbar q$ Bethe-Salpeter kernel. The resulting tetraquark equations are expressed in an exact field theoretic form, and are in agreement with those obtained previously by consideration of disconnected interactions; however, despite being more general, they have been derived here in a much simpler and more transparent way.
We derive the chiral kinetic equation in 8 dimensional phase space in non-Abelian $SU(N)$ gauge field within the Wigner function formalism. By using the covariant gradient expansion, we disentangle the Wigner equations in four-vector space up to the
The problem of causality is analyzed in the context of Local Quantum Field Theory. Contrary to recent claims, it is shown that apparent noncausal behaviour is due to a lack of the notion of sharp localizability for a relativistic quantum system. (Replaced corrupted file)
The evolution of the distribution-theoretic methods in perturbative quantum field theory is reviewed starting from Bogolyubovs pioneering 1952 work with emphasis on the theory and calculations of perturbation theory integrals.
We briefly review general concepts of renormalization in quantum field theory and discuss their application to solutions of integral equations with singular potentials in the few-nucleon sector of the low-energy effective field theory of QCD. We also
Tunneling in quantum field theory is worth understanding properly, not least because it controls the long term fate of our universe. There are however, a number of features of tunneling rate calculations which lack a desirable transparency, such as t