arXiv subjects

A. Sulaksono

Publications and source records attributed to A. Sulaksono.

52 records · Page 3Linked to original sources

arXiv2008

Low-Density Instability of Multi-Component Matter with Trapped Neutrinos

The effect of neutrino trapping on the longitudinal dielectric function at low densities has been investigated by using different relativistic mean field models. Parameter sets G2 of Furnstahl-Serot-Tang and Z271 of Horowitz-Piekarewicz, along with the adjusted parameter sets of both models, have been used in this study. The role of the isovector adjustment and the effect of the Coulomb interaction have been also studied. The effect of the isovector adjustment is found to be more significant in the Horowitz-Piekarewicz model, not only in the neutrinoless matter, but also in the matter with neutrino trapping. Although almost independent to the variation of the leptonic fraction, the instability region of matter with neutrino trapping is found to be larger. The presence of more protons and electrons compared to the neutrinoless case is the reason behind this finding. For parameter sets with soft equation of states at low density, the appearance of a large and negative epsilon_L (q, q0 = 0) in some parts of the edge of the instability region in matter with neutrino trapping is understood as a consequence of the fact that the Coulomb interaction produced by electrons and protons interaction is larger than the repulsive isovector interaction created by the asymmetry between the proton and neutron numbers.

nucl-th↗

arXiv2007

Instabilities of relativistic mean field models and the role of nonlinear terms

The instability of nuclear matter due to particle-hole excitation modes has been studied in the frame-work of several relativistic mean field (RMF) models. It is found that both the longitudinal and the transversal modes depend sensitively on the parameter sets used. The important impact of the vector and vector-scalar nonlinear terms on the stability of both modes is demonstrated. Our finding corroborates the result of previous studies, namely that certain RMF models cannot be used in high density applications. However, we show that for certain parameter sets of RMF models this shortcoming can be alleviated by adding these nonlinear terms.

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arXiv2007

From self-consistent covariant effective field theories to their Galilean-invariant counterparts

We discuss how to obtain the nonrelativistic limit of a self-consistent relativistic effective field theory for dynamic problems. It is shown that the standard v/c expansions yields Galilean invariance only to first order in v/c, whereas second order is required to obtain important contributions such as the spin-orbit force. We propose a modified procedure which is a mapping rather than a strict v/c expansion.

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arXiv2007

Multipole approach for photo- and electroproduction of kaon

We have analyzed the experimental data on K+Lambda photoproduction by using a multipole approach. In this analysis we use the background amplitudes constructed from appropriate Feynman diagrams in a gauge-invariant and crossing-symmetric fashion. Results of our analysis reveal the problem of mutual consistency between the new SAPHIR and CLAS data. We found that the problem could lead to different conclusions on ``missing resonances''. We have also extended our analysis to the finite Q^2 region and compared the result with the corresponding electroproduction data.

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arXiv2006

Kaon photoproduction in a multipole approach

The recently published experimental data on K+Lambda photoproduction by the SAPHIR, CLAS, and LEPS collaborations are analyzed by means of a multipole approach. For this purpose the background amplitudes are constructed from appropriate Feynman diagrams in a gauge-invariant and crossing-symmetric fashion. The results of our calculation emphasize the lack of mutual consistency between the SAPHIR and CLAS data previously found by several independent research groups, whereas the LEPS data are found to be more consistent with those of CLAS. The use of SAPHIR and CLAS data, individually or simultaneously, leads to quite different resonance parameters which, therefore, could lead to different conclusions on ``missing resonances''. Fitting to the SAPHIR and LEPS data simultaneously indicates that the S_{11}(1650), P_{13}(1720), D_{13}(1700), D_{13}(2080), F_{15}(1680), and F_{15}(2000) resonances are required, while fitting to the combination of CLAS and LEPS data leads alternatively to the P_{13}(1900), D_{13}(2080), D_{15}(1675), F_{15}(1680), and F_{17}(1990) resonances. Although yielding different results in most cases, both SAPHIR and CLAS data indicate that the second peak in the cross sections at W = 1900 MeV originates from the D_{13}(2080) resonance with a mass between 1911 - 1936 MeV. Furthermore, in contrast to the results of currently available models and the Table of Particle Properties, both data sets do not exhibit the need for a P_{11}(1710) resonance. The few data points available for target asymmetry can not be described by the models proposed in the present work.

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arXiv2006

Low Densities Instability of Relativistic Mean Field Models

The effects of the symmetry energy softening of the relativistic mean field (RMF) models on the properties of matter with neutrino trapping are investigated. It is found that the effects are less significant than those in the case without neutrino trapping. The weak dependence of the equation of state on the symmetry energy is shown as the main reason of this finding. Using different RMF models the dynamical instabilities of uniform matters, with and without neutrino trapping, have been also studied. The interplay between the dominant contribution of the variation of matter composition and the role of effective masses of mesons and nucleons leads to higher critical densities for matter with neutrino trapping. Furthermore, the predicted critical density is insensitive to the number of trapped neutrinos as well as to the RMF model used in the investigation. It is also found that additional nonlinear terms in the Horowitz-Piekarewicz and Furnstahl-Serot-Tang models prevent another kind of instability, which occurs at relatively high densities. The reason is that the effective sigma meson mass in their models increases as a function of the matter density.

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arXiv2006

Effects of the neutrino electromagnetic form factors on the neutrino and antineutrino mean free paths in dense matter

We have studied the effects of the nucleon weak magnetism and the neutrino electromagnetic properties on the neutrino and antineutrino mean free paths for all types of neutrinos. In the calculation, we consider matters with and without neutrino trapping as the target. We have found that the difference between the two mean free paths depends not only on the neutrino energy, but also on the matter density as well as matter constituents. Compared to the nucleon weak magnetism, the neutrino electromagnetic properties are found to have negligible effects on this difference.

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arXiv2006

Neutrino Electromagnetic Form Factors Effect on the Neutrino Cross Section in Dense Matter

The sensitivity of the differential cross section of the interaction between neutrino-electron with dense matter to the possibly nonzero neutrino electromagnetic properties has been investigated. Here, the relativistic mean field model inspired by effective field theory has been used to describe non strange dense matter, both with and without the neutrino trapping. We have found that the cross section becomes more sensitive to the constituent distribution of the matter, once electromagnetic properties of the neutrino are taken into account. The effects of electromagnetic properties of neutrino on the cross section become more significant for the neutrino magnetic moment mu_nu > 10^{-10} mu_B and for the neutrino charge radius R > 10^{-5} MeV^{-1}.

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arXiv2005

Relativistic Mean Field Models at High Densities

The effects of vector-isovector terms predicted by relativistic mean field models based on effective field theory on the equation of state and the neutrino mean free path in neutron stars have been studied. Using a procedure similar to Ref. [1] in treating the isovector sector, a parameter set (G2*) that predicts a much smaller proton fraction than the standard one (G2) can be obtained. We found that the G2* has a softer equation of state compared to the G2 at higher densities and the disappearance of the anomalous behavior of the neutrino mean free path in neutron star does not depend on the proton fraction.

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arXiv2005

Isovector Channel Role of Relativistic Mean Field Models in the Neutrino Mean Free Path

An improvement in the treatment of the isovector channel of relativistic mean field (RMF) models based on effective field theory (E-RMF) is suggested, by adding an isovector scalar (delta) meson and using a similar procedure to the one used by Horowitz and Piekarewicz to adjust the isovector-vector channel in order to achieve a softer density dependent symmetry energy of the nuclear matter at high density. Their effects on the equation of state (EOS) at high density and on the neutrino mean free path (NMFP) in neutron stars are discussed.

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arXiv2005

Nilsson parameters kappa and mu in the relativistic mean field models

Nilsson parameters kappa and mu have been studied in the framework of the relativistic mean field (RMF) models. They are used to investigate the reason that the RMF models give a relatively well prediction of the spin-orbit splitting, but fail to reproduce the placement of the states with different orbital angular momenta. Instead of the relatively small effective mass M*, the independence of M* from the angular momentum l is found to be the reason.

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arXiv2005

Neutrino Electromagnetic Form Factor and Oscillation Effects on Neutrino Interaction With Dense Matter

The mean free path of neutrino - free electron gas interaction has been calculated by taking into account the neutrino electromagnetic form factors and the possibility of neutrino oscillation. It is shown that the form factor effect becomes significant for a neutrino magnetic moment μ_ν> 10^{-10} mu_B and for a neutrino radius R > 10^{-6} MeV^{-1}. The mean free path is found to be sensitive to the nu_e-nu_mu and nu_e-nu_e^R transition probabilities.

hep-ph↗

arXiv2004

Neutron Fraction and Neutrino Mean Free Path Predictions in Relativistic Mean Field Models

The equation of state (EOS) of dense matter and neutrino mean free path (NMFP) in a neutron star have been studied by using relativistic mean field models motivated by effective field theory (ERMF). It is found that the models predict too large proton fractions, although one of the models (G2) predicts an acceptable EOS. This is caused by the isovector terms. Except G2, the other two models predict anomalous NMFP. In order to minimize the anomaly, besides an acceptable EOS, a large M* is favorable. A model with large M* retains the regularity in the NMFP even for a small neutron fraction.

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arXiv2004

Missing Resonances in Kaon Photoproduction on the Nucleon

New kaon photoproduction data on a proton, gamma + p --> K+ + Lambda, are analyzed using a multipole approach. The background terms are given in terms of gauge invariant, crossing symmetric, Born diagrams with hadronic form factors, while the resonances are parameterized using Breit-Wigner forms. Preliminary results suggest a number of new resonances, as predicted by many quark model studies. A comparison between the extracted multipoles and those obtained from KAON-MAID is presented.

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arXiv2003

The nonrelativistic limit of the relativistic point coupling model

We relate the relativistic finite range mean-field model (RMF-FR) to the point-coupling variant and compare the nonlinear density dependence. From this, the effective Hamiltonian of the nonlinear point-coupling model in the nonrelativistic limit is derived. Different from the nonrelativistic models, the nonlinearity in the relativistic models automatically yields contributions in the form of a weak density dependence not only in the central potential but also in the spin-orbit potential. The central potential affects the bulk and surface properties while the spin-orbit potential is crucial for the shell structure of finite nuclei. A modification in the Skyrme-Hartree-Fock model with a density-dependent spin-orbit potential inspired by the point-coupling model is suggested.

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arXiv2003

Mapping exchange in relativistic Hartree-Fock

We show that formally for the standard ansatz relativistic point-coupling mean-field (RMF-PC) model a lagrangian density L is not equivalent in Hartree and Hartree-Fock approximations. The equivalency can be achieved only if we use a ``complete'' ansatz at the cost of introducing new parameters in the model. An approximate treatment of the exchange terms from standard RMF-PC indicates that these effects cannot be easily, if at all, absorbed by a Dirac-Hartree approximation.

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