The physical properties of two-dimensional interacting electron systems are of great current interest. An open question in the physics of low-dimensional fermionic models is whether their properties are described by standard Fermi-liquid theory or whether instead they show unconventional behaviour in strongly correlated electron systems. As the two-dimensional Hubbard model is the typical example of a strongly correlated electron system, we solve for this model the two-body problem in the vicinity of a half-filled Fermi sea. The results obtained show that for a low hole concentration the well known Fermi-liquid picture fails.
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