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Fri, 14 Jul 2006 10:15:51 +0200Fri, 14 Jul 2006 10:15:51 +0200Structure of the vacuum in nuclear matter: a nonperturbative approach
http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2383
We compute the vacuum polarization correction to the binding energy of nuclear matter in the Walecka model using a nonperturbative approach. We first study such a contribution as arising from a ground-state structure with baryon-antibaryon condensates. This yields the same results as obtained through the relativistic Hartree approximation of summing tadpole diagrams for the baryon propagator. Such a vacuum is then generalized to include quantum effects from meson fields through scalar-meson condensates which amounts to summing over a class of multiloop diagrams. The method is applied to study properties of nuclear matter and leads to a softer equation of state giving a lower value of the incompressibility than would be reached without quantum effects. The density-dependent effective sigma mass is also calculated including such vacuum polarization effects.Amruta Mishra; P. K. Panda; Stefan Schramm; Joachim Reinhardt; Walter Greinerarticlehttp://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2383Fri, 14 Jul 2006 10:15:51 +0200Coulomb effects on electromagnetic pair production in ultrarelativistic heavy-ion collisions
http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2391
We calculate the asymptotic high-energy amplitude for electrons scattering at one ion, as well as at two colliding ions, by means of perturbation theory. We show that the interaction with one ion eikonalizes and that the interaction with two ions causally decouples. We are able to put previous results on perturbative grounds and propose further applications for the obtained rules for interactions on the light cone. We discuss the implications of the eikonal amplitude on the pair production probability in ultrarelativistic peripheral heavy-ion collisions. In this context the WeizsĂ¤cker-Williams method is shown to be exact in the ultrarelativistic limit, irrespective of the produced particlesâ€™ mass. A new equivalent single-photon distribution is derived, which correctly accounts for Coulomb distortions. The impact on single-photon induced processes is discussed.U. Eichmann; Joachim Reinhardt; Stefan Schramm; Walter Greinerarticlehttp://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2391Fri, 14 Jul 2006 10:12:20 +0200