Detlef Lehmann

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We prove that the global minimum of the real part of the full effective potential of the many electron system with attractive delta interaction is in fact given by the BCS mean field configuration. This is a consequence of a simple bound which is obtained by applying Hadamard's inequality to the functional determinant. The second order Taylor expansion(More)
In these lectures, we consider a many-body system that is somewhat unusual in that the Fermi surface survives the turning on of all suuciently weak short range interactions. The system consists of a gas of fermions with prescribed, strictly positive, density, together with a crystal lattice of magnetic ions. The fermions interact with each other through a(More)
In an effective theory containing only quark degrees of freedom, such as the extended Nambu–Jona–Lasinio model, the influence of the axial anomaly can be incorporated by a self-interaction of the 't Hooft determinant type. I will show that this leads to a significant suppression of the η ′ coupling g η ′ qq to dynamical quarks which suggests a suppression(More)
In an eeective theory containing only quark degrees of freedom, such as the extended Nambu{Jona{Lasinio model, the innuence of the axial anomaly can be incorporated by a self-interaction of the 't Hooft determinant type. I will show that this leads to a signiicant suppression of the 0 coupling g 0 qq to dynamical quarks which suggests a suppression of the 0(More)