Extremely correlated limit of the Hubbard model

In this work, we describe the simplifications to the Extremely Correlated Fermi Liquid Theory (ECFL) which occur in the limit of infinite spatial dimensions. In particular, we show that the single-particle electron Green's function G(k) can be written in terms of two momentum-independent self-energies. Moreover, we elucidate the nature of the ECFL lambda expansion in the limit of infinite dimensions and carry out this expansion explicitly to O(lambda 2). Additionally, we demonstrate the vanishing of vertex corrections to the optical conductivity in general and to each order in lambda in the limit of infinite dimensions. We generalize the ECFL formalism to the infinite- U Anderson impurity model (AIM) , and demonstrate a Dynamical Mean-Field Theory (DMFT) like mapping between the ECFL objects of the infinite-dimensional t-J model and the infinite-U AIM, and show that this mapping holds to each order in lambda. We compute the spectral function for the AIM to O (lambda2) and make comparisons with results obtained through Numerical Renormalization Group (NRG) computations. Finally, we develop a novel formalism for the high-temperature expansion of dynamical correlation functions in the infinite-U Hubbard model which is more efficient than any used previously and gives results for an arbitrary number of spin species. We use it to calculate the single-particle Green's function G(k) to fourth order in (betat) for m spin-species on a d-dimensional hypercube.