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Register a new userAngle-dependent Gap state in Asymmetric Nuclear Matter
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We propose an axisymmetric angle-dependent gap (ADG) state with the broken rotational symmetry in isospin-asymmetric nuclear matter. In this state, the deformed Fermi spheres of neutrons and protons increase the pairing probabilities along the axis of symmetry breaking near the average Fermi surface. We find that the state possesses lower free energy and larger gap value than the angle-averaged gap state at large isospin asymmetries. These properties are mainly caused by the coupling of different m_{j} components of the pairing gap. Furthermore, we find the transition from the ADG state to the normal state is of second order and the ADG state vanishes at the critical isospin asymmetry m_{j} where the angle-averaged gap vanishes.
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We consider the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state with an angle dependent-gap (ADG) for the arbitrary angle theta_0 between the direction of the Cooper pair momentum and the symmetry axis of the ADG in asymmetric nuclear matter. We find two kinds of locally stable states, i.e., the FFLO-ADG-orthogonal and FFLO-ADG-parallel states, which correspond to theta_0=pi/2 and theta_0=0, respectively. Furthermore, the-FFLO-ADG-orthogonal state is located at small asymmetry, whereas the FFLO-ADG-parallel state is favored for large asymmetry. The critical isospin asymmetry alpha_c, where the superfluid vanishes, is enhanced largely by considering the Cooper pair momentum with an ADG.
Density dependent parametrization models of the nucleon-meson effective couplings, including the isovector scalar delta-field, are applied to asymmetric nuclear matter. The nuclear equation of state and the neutron star properties are studied in an effective Lagrangian density approach, using the relativistic mean field hadron theory. It is known that the introduction of a delta-meson in the constant coupling scheme leads to an increase of the symmetry energy at high density and so to larger neutron star masses, in a pure nucleon-lepton scheme. We use here a more microscopic density dependent model of the nucleon-meson couplings to study the properties of neutron star matter and to re-examine the delta-field effects in asymmetric nuclear matter. Our calculations show that, due to the increase of the effective delta coupling at high density, with density dependent couplings the neutron star masses in fact can be even reduced.
The existence of phase transitions from liquid to gas phases in asymmetric nuclear matter (ANM) is related with the instability regions which are limited by the spinodals. In this work we investigate the instabilities in ANM described within relativistic mean field hadron models, both with constant and density dependent couplings at zero and finite temperatures. In calculating the proton and neutron chemical potentials we have used an expansion in terms of Bessel functions that is convenient at low densities. The role of the isovector scalar $delta$-meson is also investigated in the framework of relativistic mean field models and density dependent hadronic models. It is shown that the main differences occur at finite temperature and large isospin asymmetry close to the boundary of the instability regions.
The dynamic response of asymmetric nuclear matter is studied by using a Time-Dependent Local Isospin Density (TDLIDA) approximation approach. Calculations are based on a local density energy functional derived by an Auxiliary Field Diffusion Monte Carlo (AFDMC) calculation of bulk nuclear matter. Three types of excited states emerge: collective states, a continuum of quasi-particle-quasi-hole excitations and unstable solutions. These states are analyzed and discussed for different values of the nuclear density $rho$ and isospin asymmetry $xi=(N-Z)/A$. An analytical expression of the compressibility as a function of $rho$ and $xi$ is derived which show explicitly an instability of the neutron matter around $rhosimeq 0.09 fm^{-3}$ when a small fraction of protons is added to the system.
The directed flow of identified hadrons is studied within the parton-hadron-string-dynamics (PHSD) approach for the asymmetric system Cu+Au in non-central collisions at $sqrt{s_{NN}}$ = 200 GeV. It is emphasized that due to the difference in the number of protons of the colliding nuclei an electric field emerges which is directed from the heavy to the light nucleus. This strong electric field is only present for about 0.25 fm/c at $sqrt{s_{NN}}$ = 200 GeV and leads to a splitting of the directed flow $v_1$ for particles with the same mass but opposite electric charges in case of an early presence of charged quarks and antiquarks. The microscopic calculations of the directed flow for $pi^pm, K^pm, p$ and $bar{p}$ are carried out in the PHSD by taking into account the electromagnetic field induced by the spectators as well as its influence on the hadronic and partonic quasiparticle trajectories. It is shown that the splitting of the directed flow as a function of pseudorapidity $eta$ and in particular as a function of the transverse momentum $p_t$ provides a direct access to the electromagnetic response of the very early (nonequilibrium) phase of relativistic heavy-ion collisions and allows to shed light on the presence (and number) of electric charges in this phase.
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