Nuclear matter

About: Nuclear matter is a research topic. Over the lifetime, 10180 publications have been published within this topic receiving 248261 citations.

In-medium chiral condensate beyond linear density approximation

Abstract: In-medium chiral perturbation theory is used to calculate the density dependence of the quark condensate . The corrections beyond the linear density approximation are obtained by differentiating the interaction contributions to the energy per particle of isospin-symmetric nuclear matter with respect to the pion mass. Our calculation treats systematically the effects from one-pion exchange (with m{sub {pi}}-dependent vertex corrections), iterated 1{pi}-exchange, and irreducible 2{pi}-exchange including intermediate {delta}(1232)-isobar excitations, with Pauli-blocking corrections up to three-loop order. We find a strong and nonlinear dependence of the ''dropping'' in-medium condensate on the actual value of the pion (or light quark) mass. In the chiral limit, m{sub {pi}}=0, chiral restoration appears to be reached already at about 1.5 times normal nuclear matter density. By contrast, for the physical pion mass, m{sub {pi}}=135 MeV, the in-medium condensate stabilizes at about 60% of its vacuum value above that same density. Effects from 2{pi}-exchange with virtual {delta}(1232)-isobar excitations turn out to be crucial in generating such pronounced deviations from the linear density approximation above {rho}{sub 0}. The hindered tendency toward chiral symmetry restoration provides a justification for using pions and nucleons as effective low-energy degrees of freedom at least up to twice nuclear matter density.

Self-consistent Hartree description of deformed nuclei in a relativistic quantum field theory

Abstract: Relativistic Hartree orbitals for nonspherical (even-even) nuclei have been calculated self-consistently from a Lagrangian field theory using the mean field approximation. All parameters in this model are determined from the properties of infinite nuclear matter, so there are no parameters which can be adjusted in the calculation of the orbitals. The energy levels, rms radii, and quadrupole moments are in qualitative agreement with earlier nonrelativistic calculations and with experiment; however, the overall deformations (which are fixed by the self-consistency) are somewhat smaller than those obtained experimentally and from nonrelativistic calculations. The difference may be due to the large compressibility characteristic of relativistic mean field calculations. These orbitals and the self-consistently determined mean fields provide a framework for a detailed investigation of the compressibility as well as other relativistic effects.

Spin-dependent structure functions in nuclear matter and the polarized EMC effect.

Abstract: An excellent description of both spin-independent and spin-dependent quark distributions and structure functions has been obtained with a modified Nambu-Jona-Lasinio model, which is free of unphysical thresholds for nucleon decay into quarks--hence incorporating an important aspect of confinement. We utilize this model to investigate nuclear medium modifications to structure functions and find that we are readily able to reproduce both nuclear matter saturation and the experimental F{sub 2N}{sup A}/F{sub 2N} ratio, that is, the European Muon Collaboration (EMC) effect. Applying this framework to determine g{sub 1p}{sup A}, we find that the ratio g{sub 1p}{sup A}/g{sub 1p} differs significantly from unity, with the quenching caused by the nuclear medium being about twice that of the spin-independent case. This represents an exciting result, which, if confirmed experimentally, will reveal much about the quark structure of nuclear matter.