A strong-coupling series expansion for the Green's function and the extremely correlated Fermi liquid (ECFL) theory are used to calculate the moments of the electronic spectral functions of the infinite-U Hubbard model. Results from these two complementary methods agree very well at both low densities, where the ECFL solution is the most accurate, and at high to intermediate temperatures, where the series converge. We find that a modified first moment, which underestimates the contributions from the occupied states and is accessible in the series through the time-dependent Green's function, best describes the peak location of the spectral function in the strongly correlated regime. This is examined by the ECFL results at low temperatures, where it is shown that the spectral function is largely skewed towards the occupied states.
Ehsan Khatami, Daniel Hansen, Edward Perepelitsky, Marcos Rigol, and Sriram Shastry. "Electronic spectral properties of the two-dimensional infinite-U Hubbard model" Physical Review B (2013). doi:10.1103/PhysRevB.87.161120