Extremely Correlated Fermi Liquids

We present the theory of an extremely correlated Fermi liquid (ECFL) with $U\to \infty$. This liquid has an underlying Fermi liquid (FL) Greens function that is further caparisoned. The theory leads to two parallel hierarchies of equations that permit iterative approximations in a certain parameter. Preliminary results for the spectral functions display a broad background and a distinct $T$ dependent left skew. An important energy scale $\Delta(\vec{k},x)$ emerges as the average inelasticity of the FL Greens function, and influences the photoemission spectra profoundly. A duality is identified wherein an apparent loss of coherence of the ECFL results from an excessively sharp FL.