Probabilities in nonorthogonal basis: Four--quark systems

Four-quark states may exist as colorless meson-meson molecules or compact systems with two-body colored components. We derive an analytical procedure to expand an arbitrary four–quark wave function in terms of nonorthogonal color singlet–singlet vectors. Using this expansion we develop the necessary formalism to evaluate the probability of physical components with an arbitrary four-quark wave function. Its application to characterize bound and unbound four–quark states as meson-meson, molecular or compact systems is discussed