2,880 research outputs found

    Screening Effects in Superfluid Nuclear and Neutron Matter within Brueckner Theory

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    Effects of medium polarization are studied for 1S0^1S_0 pairing in neutron and nuclear matter. The screening potential is calculated in the RPA limit, suitably renormalized to cure the low density mechanical instability of nuclear matter. The selfenergy corrections are consistently included resulting in a strong depletion of the Fermi surface. All medium effects are calculated based on the Brueckner theory. The 1S0^1S_0 gap is determined from the generalized gap equation. The selfenergy corrections always lead to a quenching of the gap, which is enhanced by the screening effect of the pairing potential in neutron matter, whereas it is almost completely compensated by the antiscreening effect in nuclear matter.Comment: 8 pages, 6 Postscript figure

    Spin-polarized states of nuclear matter

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    The equations of state of spin-polarized nuclear matter and pure neutron matter are studied in the framework of the Brueckner-Hartree-Fock theory including a three-body force. The energy per nucleon EA(δ)E_A(\delta) calculated in the full range of spin polarization δ=ρρρ{\delta} = \frac{\rho_{\uparrow}-\rho_{\downarrow}}{\rho} for symmetric nuclear matter and pure neutron matter fulfills a parabolic law. In both cases the spin-symmetry energy is calculated as a function of the baryonic density along with the related quantities such as the magnetic susceptibility and the Landau parameter G0G_0. The main effect of the three-body force is to strongly reduce the degenerate Fermi gas magnetic susceptibility even more than the value with only two body force. The EOS is monotonically increasing with the density for all spin-aligned configurations studied here so that no any signature is found for a spontaneous transition to a ferromagnetic state.Comment: Contribution to GISELDA Meeting, 14-18 January, 2002 (Frascati), to appear in World Scientific (Singapore

    Transport parameters in neutron stars from in-medium NN cross sections

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    We present a numerical study of shear viscosity and thermal conductivity of symmetric nuclear matter, pure neutron matter and β\beta-stable nuclear matter, in the framework of the Brueckner theory. The calculation of in-medium cross sections and nucleon effective masses is performed with a consistent two and three body interaction. The investigation covers a wide baryon density range as requested in the applications to neutron stars. The results for the transport coefficients in β\beta-stable nuclear matter are used to make preliminary predictions on the damping time scales of non radial modes in neutron stars

    Isospin singlet (pn) pairing and quartetting contribution to the binding energy of nuclei

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    Isospin singlet (pn) pairing as well as quartetting in nuclei is expected to arise near the symmetry line N=ZN=Z. Empirical values can be deduced from the nuclear binding energies applying special filters. Within the local density approximation, theoretical estimates for finite nuclei are obtained from results for the condensation energy of asymmetric nuclear matter. It is shown that the isospin singlet condensation energy drops down abruptly for |N-Z|~4 for medium nuclei in the region A=40. Furthermore, alpha-like quartetting and the influence of excitations are discussed.Comment: 19 pages, 19 figures, submitted to PR

    Microscopic three-body force for asymmetric nuclear matter

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    Brueckner calculations including a microscopic three-body force have been extended to isospin asymmetric nuclear matter. The effects of the three-body force on the equation of state and on the single-particle properties of nuclear matter are discussed with a view to possible applications in nuclear physics and astrophysics. It is shown that, even in the presence of the three-body force, the empirical parabolic law of the energy per nucleon vs isospin asymmetry β=(NZ)/A\beta=(N-Z)/A is fulfilled in the whole asymmetry range 0β10\le\beta\le 1 up to high densities. The three-body force provides a strong enhancement of symmetry energy increasing with the density in good agreement with relativistic approaches. The Lane's assumption that proton and neutron mean fields linearly vary vs the isospin parameter is violated at high density in the presence of the three-body force. Instead the momentum dependence of the mean fields is rather insensitive to three body force which brings about a linear isospin deviation of the neutron and proton effective masses. The isospin effects on multifragmentation events and collective flows in heavy-ion collisions are briefly discussed along with the conditions for direct URCA processes to occur in the neutron-star cooling.Comment: 11 pages, 7 figure

    Screening of nuclear pairing in nuclear and neutron matter

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    The screening potential in the 1S0^1S_0 and 3S1^3S_1 pairing channels in neutron and nuclear matter in different approximations is discussed. It is found that the vertex corrections to the potential are much stronger in nuclear matter than in neutron matter.Comment: 11 pages, 8 figures, revtex4 styl

    Medium polarization in asymmetric nuclear matter

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    The influence of the core polarization on the effective nuclear interaction of asymmetric nuclear matter is calculated in the framework of the induced interaction theory. The strong isospin dependence of the density and spin density fluctuations is studied along with the interplay between the neutron and proton core polarizations. Moving from symmetric nuclear matter to pure neutron matter the crossover of the induced interaction from attractive to repulsive in the spin singlet state is determined as a function of the isospin imbalance.The density range in which it occurs is also determined. For the spin triplet state the induced interaction turns out to be always repulsive. The implications of the results for the neutron star superfluid phases are shortly discussed.Comment: 6 pages, 4 figure
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