  The Mott metal-insulator transition in the Hubbard model is studied by
constructing a dynamical slave-boson mean-field theory in the limit of large
lattice coordination number $z$ that incorporates the binding between doubly
occupied (doublon) and empty (holon) sites. On the Mott insulating side where
all doublons and holons bond in real space into excitonic pairs leading to the
charge gap, the theory simplifies considerably to leading order in
$1/\sqrt{z}$, and becomes exact on the infinite-$z$ Bethe lattice. An
asymptotic solution is obtained for a continuous Mott transition associated
with the closing of the charge gap at a critical value of the Hubbard $U_c$ and
the corresponding doublon density $n_d^c$, hopping $\chi_d^c$ and doublon-holon
pairing $\Delta_d^c$ amplitudes. We find $U_c=U_{\rm BR} [1 -2n_d^c -\sqrt{z}
(\chi_d^c +\Delta_d^c))] \simeq0.8U_{\rm BR}$, where $U_{\rm BR}$ is the
critical value for the Brinkman-Rice transition in the Gutzwiller approximation
captured in the static mean-field solution of the slave-boson formulation of
Kotliar and Ruckenstein. Thus, the Mott transition can be viewed as the quantum
correction to the Brinkman-Rice transition due to doublon-holon binding.
Quantitative comparisons are made to the results of the dynamical mean-field
theory, showing good agreement. In the absence of magnetic order, the Mott
insulator is a $U(1)$ quantum spin liquid with nonzero intersite spinon hopping
that survives the large-$z$ limit and lifts the $2^N$-fold degeneracy of the
local moments. We show that the spinons are coupled to the doublons/holons by a
dissipative compact $U(1)$ gauge field in the deconfined phase, realizing the
spin-charge separated gapless spin liquid Mott insulator.
