Representations in Density Dependent Hadronic Field Theory and compatibility with QCD sum-rules

Different representations of an effective, covariant theory of the hadronic interaction are examined. For this purpose we have introduced nucleon-meson vertices parametrized in terms of scalar combinations of hadronic fields, extending the conceptual frame of the Density Dependent Hadronic Field Theory. Nuclear matter properties at zero temperature are examined in the Mean Field Approximation, including the equation of state, the Landau parameters, and collective modes. The treatment of isospin channels in terms of QCD sum rules inputs is outlined.Comment: 23 pages, 6 PostScript figures, Revtex4 clas

Relativistic models of the neutron-star matter equation of state

Motivated by a recent astrophysical measurement of the pressure of cold matter above nuclear-matter saturation density, we compute the equation of state of neutron star matter using accurately calibrated relativistic models. The uniform stellar core is assumed to consist of nucleons and leptons in beta equilibrium; no exotic degrees of freedom are included. We found the predictions of these models to be in fairly good agreement with the measured equation of state. Yet the Mass-vs-Radius relations predicted by these same models display radii that are consistently larger than the observations.Comment: Submitted to Physical Review C (5 pages with 2 figures and 2 tables

Impact of spin-orbit currents on the electroweak skin of neutron-rich nuclei

Background: Measurements of neutron radii provide important constraints on the isovector sector of nuclear density functionals and offer vital guidance in areas as diverse as atomic parity violation, heavy-ion collisions, and neutron-star structure. Purpose: To assess the impact of spin-orbit currents on the electromagnetic- and weak-charge radii of a variety of nuclei. Special emphasis is placed on the experimentally accessible electroweak skin, defined as the difference between weak-charge and electromagnetic-charge radii. Methods: Two accurately calibrated relativistic mean field models are used to compute proton, neutron, charge, and weak-charge radii of a variety of nuclei. Results: We find that spin-orbit contributions to the electroweak skin of light neutron-rich nuclei, such as 22O and 48Ca, are significant and result in a substantial increase in the size of the electroweak skin relative to the neutron skin. Conclusions: Given that spin-orbit contributions to both the charge and weak-charge radii of nuclei are often as large as present or anticipated experimental error bars, future calculations must incorporate spin-orbit currents in the calculation of electroweak form factors.Comment: 17 pages, 2 figures, and 2 table

Dirac Sea Contribution in Relativistic Random Phase Approximation

In the hadrodynamics (QHD) there are two methods to take account of the contribution of negative-energy states in the relativistic random phase approximation (RRPA). Dawson and Furnstahl made the ansatz that the Dirac sea were empty, while according to the Dirac hole theory the sea should be fully occupied. The two methods seem contradictory. Their close relationship and compatibility are explored and in particular the question of the ground-state (GS) instability resulting from Dawson-Furnstanhl's ansatz is discussed.Comment: 17 pages, 4 figures (the revised version.The paper and figures are revised). accepted by J. Phys.

Superfluidity of Λ\Lambda hyperons in neutron stars

We study the $^1S_0$ superfluidity of $\Lambda$ hyperons in neutron star matter and neutron stars. We use the relativistic mean field (RMF) theory to calculate the properties of neutron star matter. In the RMF approach, the meson-hyperon couplings are constrained by reasonable hyperon potentials that include the updated information from recent developments in hypernuclear physics. To examine the $^1S_0$ pairing gap of $\Lambda$ hyperons, we employ several $\Lambda\Lambda$ interactions based on the Nijmegen models and used in double-$\Lambda$ hypernuclei studies. It is found that the maximal pairing gap obtained is a few tenths of a MeV. The magnitude and the density region of the pairing gap are dependent on the $\Lambda\Lambda$ interaction and the treatment of neutron star matter. We calculate neutron star properties and find that whether the $^1S_0$ superfluidity of $\Lambda$ hyperons exists in the core of neutron stars mainly depends on the $\Lambda\Lambda$ interaction used.Comment: 22 pages, 2 Tables, 6 Figur

Integrating out the Dirac sea in the Walecka model

We derive a purely fermionic no-sea effective theory, featuring positive-energy states only for the Walecka model. In contrast to the so-called mean-field theory approach with the no-sea approximation, where the Dirac sea is simply omitted from the outset, we turn to the relativistic Hartree approximation and explicitly construct a no-sea effective theory from the underlying quantum field theory. Several results obtained within these two approaches are confronted with each other. This sheds new light on the reliability of the mean-field theory with the no-sea approximation as well as the role of the Dirac sea. Restricting to 1+1 dimensions, we obtain new analytical insights into nonuniform nuclear matter.Comment: 15 pages, 8 figures, several points clarified, Fig.7 replaced, references adde

Melting of antikaon condensate in protoneutron stars

We study the melting of a $K^-$ condensate in hot and neutrino-trapped protoneutron stars. In this connection, we adopt relativistic field theoretical models to describe the hadronic and condensed phases. It is observed that the critical temperature of antikaon condensation is enhanced as baryon density increases. For a fixed baryon density, the critical temperature of antikaon condensation in a protoneutron star is smaller than that of a neutron star. We also exhibit the phase diagram of a protoneutron star with a $K^-$ condensate.Comment: 17 pages including 7 figure

Neutral-current neutrino-nucleus cross sections based on relativistic nuclear energy density functional

Background: Inelastic neutrino-nucleus scattering through the weak neutral-current plays important role in stellar environment where transport of neutrinos determine the rate of cooling. Since there are no direct experimental data on neutral-current neutrino-nucleus cross sections available, only the modeling of these reactions provides the relevant input for supernova simulations. Purpose: To establish fully self-consistent framework for neutral-current neutrino-nucleus reactions based on relativistic nuclear energy density functional. Methods: Neutrino-nucleus cross sections are calculated using weak Hamiltonian and nuclear properties of initial and excited states are obtained with relativistic Hartree-Bogoliubov model and relativistic quasiparticle random phase approximation that is extended to include pion contributions for unnatural parity transitions. Results: Inelastic neutral-current neutrino-nucleus cross sections for 12C, 16O, 56Fe, 56Ni, and even isotopes {92-100}Mo as well as respective cross sections averaged over distribution of supernova neutrinos. Conclusions: The present study provides insight into neutrino-nucleus scattering cross sections in the neutral channel, their theoretical uncertainty in view of recently developed microscopic models, and paves the way for systematic self-consistent large-scale calculations involving open-shell target nuclei.Comment: 25 pages, 9 figures, 2 tables, submitted to Physical Review

Integrating out the Dirac sea: Effective field theory approach to exactly solvable four-fermion models

We use 1+1 dimensional large N Gross-Neveu models as a laboratory to derive microscopically effective Lagrangians for positive energy fermions only. When applied to baryons, the Euler-Lagrange equation for these effective theories assumes the form of a non-linear Dirac equation. Its solution reproduces the full semi-classical results including the Dirac sea to any desired accuracy. Dynamical effects from the Dirac sea are encoded in higher order derivative terms and multi-fermion interactions with perturbatively calculable, finite coefficients. Characteristic differences between models with discrete and continuous chiral symmetry are observed and clarified.Comment: 13 pages, 11 figures; v2: typos corrected (Eqs. 4 and 44

Analysis of flux-integrated cross sections for quasi-elastic neutrino charged-current scattering off 12^{12}C at MiniBooNE energies

Flux-averaged and flux-integrated cross sections for quasi-elastic neutrino charged-current scattering on nucleus are analyzed. It is shown that the flux-integrated differential cross sections are nuclear model-independent. We calculate these cross sections using the relativistic distorted-wave impulse approximation and relativistic Fermi gas model with the Booster Neutrino Beamline flux and compare results with the recent MiniBooNE experiment data. Within these models an axial mass $M_A$ is extracted from a fit of the measured $d\sigma/dQ^2$ cross section. The extracted value of $M_A$ is consistent with the MiniBooNE result. The measured and calculated double differential cross sections $d\sigma/dTd\cos\theta$ generally agree within the error of the experiment. But the Fermi gas model predictions are completely off of the data in the region of low muon energies and scattering angles.Comment: 23 pages, 8 figure