Response Function Of Nuclear Matter Research Articles

Structure Functions Generated by Zero Sound Excitations

In isospin symmetric and asymmetric nuclear matter we study the structure functions connected with the zero sound excitations. In the simple model with Landau-Migdal quasiparticle interactions the density response $\Pi^R(\omega,k)$ of the nuclear matter to the small isovector external field $V_0(\omega,k)$ is considered. In the previous papers the complex branches of solutions $\omega_{si}(k)$, $i=n,p,np$ of the dispersion equation corresponding to zero sound excitations in the symmetric and asymmetric nuclear matter are obtained. Now we investigate the structure and response functions of nuclear matter based on these solutions.

Nuclear matter response function with a central plus tensor Landau interaction

We present a method to obtain response functions in the random phase approximation (RPA) based on a residual interaction described in terms of Landau parameters with central plus tensor contributions. The response functions keep the explicit momentum dependence of the RPA, in contrast with the traditional Landau approximation. Results for symmetric nuclear matter and pure neutron matter are presented using Landau parameters derived from finite-range interactions, both phenomenological and microscopic. We study the convergence of response functions as the number of Landau parameters is increased.

Dipole Response Function of Nuclear Matter with Pairing Correlations

The dipole response function of nuclear matter at finite temperature is investigated by employing a linearized Landau–Vlasov equation with pairing correlations. We calculate the giant dipole resonance strength function with and without quasiparticle collisional effects. Calculations are carried out for nuclear dipole vibrations of finite nuclei by employing the Steinwedel–Jensen model, and their results are compared with experimental results for 120 Sn.

Continued fraction approximation for the nuclear matter response function

A continued fraction approximation is used to calculate the Random Phase Approximation (RPA) response function of nuclear matter. The convergence of the approximation is assessed by comparing it with the numerically exact response function obtained with a typical effective finite-range interaction used in nuclear physics. It is shown that just the first order term of the expansion can give reliable results at densities up to the saturation density value.

Neutrino mean free path in neutron stars

The neutrino propagation in neutron stars is studied in the framework of the linear response method. The medium effects are treated in the nonrelativistic Brueckner-Hartree-Fock approach either in the mean-field approximation or in the random phase approximation. The residual interaction is expressed in terms of the Landau parameters extracted from the equation of state of spin- and isospin-polarized nuclear matter. The Brueckner theory including three-body forces is used for determining the equation of state. Numerical predictions for the response function of nuclear matter in $\ensuremath{\beta}$ equilibrium and the neutrino mean free path are presented in a range of baryonic densities and temperatures. The main results are a dominance of the charge-exchange component over the scattering component and an enhancement of the neutrino mean free path induced by nuclear correlations.

Two-body and many-body final state interaction corrections in the nuclear matter response function around the quasielastic peak

Abstract The inclusive scattering response function of nuclear matter is studied in the regime of large but non-relativistic momentum transfer q . We review the derivation leading to the complete two-particle final state interaction corrections to the impulse approximation. These are calculated with an eikonal approach and using models that we develop for the two-particle density matrix, which account for spin and isospin degrees of freedom. The two-body part gives comparable results to a many-body approximation with a sizable reduced strength in the response at values q = 550 MeV, and energy transfers ω around and beyond the quasielastic peak, and, with a finite-size approximation involving the nucleus scale, it produces oscillations. These behaviours are in accordance with data from nuclei. Our results resemble those with a hard-core interaction for which strength in the response is shifted to large values of the energy transfer ω.

Quasi-elastic Coulomb response function for finite systems and elimination of the Landau ghost in the relativistic σ-ω model

The quasi-elastic Coulomb response function of finite nuclei including vacuum polarization effects is investigated in the relativistic σ-ω model. For the consistent elimination of the Landau ghost in meson propagators, the description of the ground state and the response function of the system is formulated utilizing the effective action method, and the effects of the ghost elimination on the nuclear matter response function are discussed. Finite system calculations are performed for 12 C (|q|= 300, 400, 550 MeV) and 40 Ca (|q|= 410, 500, 550 MeV) , in which particle-hole continuum states are fully taken into account by the method of continuum RPA, while the vacuum polarization effects are included by the local density approximation. The effects of the particle-hole effective interaction and the medium modified single-nucleon form factor on the response function are also discussed.

The response function of nuclear matter

The response function of nuclear matter is derived from experimental data on inclusive electron-nucleus scattering from finite nuclei. The results are compared to theoretical calculations of nuclear matter response and spectral functions.

Tensor forces and the response functions of nuclear matter.

The response functions of nuclear matter in the region of small momentum transfer are evaluated within the framework of the random-phase approximation. The particle-hole interaction is assumed to be of the one-boson-exchange type and contains both central and tensor terms. Because of the tensor interaction six different channels, corresponding to different values of the total particle-hole spin and isospin, must be distinguished. A method that we have developed before for purely central forces is extended to the present case. This allows us to take properly into account the exchange diagrams, in the limit of small momentum transfer, even when the particle-hole interaction contains a tensor component.

Nuclear matter response function.

The response function of nuclear matter is determined from experimental data on inclusive electron scattering from finite nuclei.

Effect of vacuum fluctuations on the quasielastic response functions in quantum hadrodynamics

The longitudinal and transverse response functions for quasielastic electron scattering on 12C and 40Ca are calculated in the renormalized σωρ model of quantum hadrodynamics. We employ a local-density approximation based on renormalized response functions of nuclear matter, and local baryon densities and nucleon effective mass as obtained from renormalized mean-field theory. The results are compared with previous calculations neglecting the vacuum contributions. Due to the larger effective mass we find a shift of strength towards smaller energy transfer. This improves the slope of the response at large energy transfer in comparison with the data, but at the quasielastic peak the data are now in general overestimated for both response functions.

Response function of nuclear matter.

We propose a new method to calculate the particle-hole Green's function for an infinite system of fermions in the long-wavelength limit of the random-phase approximation. Contrary to the standard approach the present method does not require approximating the residual particle-hole interaction by a sum of separable terms. The method can also be applied to the Landau theory of Fermi liquids. We illustrate the method by evaluating the response function of nuclear matter in the long-wavelength limit for two different isospin channels.

Scaling violations in quasielastic electron scattering

We study the response function of nuclear matter using Brueckner-Goldstone perturbation theory through two hole-lines. In the quasielastic region accessible to present experiments, we find that the approach to y-scaling with increasing momentum transfer differs significantly from that of the commonly assumed Fermi gas with no final state interactions and is in reasonable accord with the data.

Correlated basis theory of nuclear matter response functions

A comprehensive correlated basis theory for calculating the response functions of nuclear matter from realistic nuclear interactions is presented. It is used to calculate the dynamic structure function of nuclear matter in an approximation in which only correlated 1p–1h excited states are retained. The effect of 2p–2h excitations are approximately included via real and imaginary parts of the optical potential. It is argued that at large values of k the longitudinal response function R L( k, ω), observed in electron scattering experiments, can be obtained from the dynamic structure function. The calculated R L ( k, ω) at k = 300 and 400 MeV/ c is in fair agreement with the data on 40Ca, 48Ca and 238U nuclei. At k = 550 MeV/ c, the calculated response is in agreement with experiments on 40Ca and 56Fe at small values of ω, while it is larger than experiment at large ω.

Backflow, retardation and relativistic effects on the longitudinal response function of nuclear matter

The relativistic RPA response function for quasielastic electron scattering in the σ − ω model is analyzed in detail. The following three effects on the longitudinal response function are examined numerically, and analytically in the relativistic Landau theory; (i) the backflow effect due to the longitudinal component of the ω-meson exchange between particle-hole states, (ii) the relativistic effect from the difference between the Lorentz scalar and baryon densities, and (iii) the retardation effect of the particle-hole interactions. The first two effects, which are neglected in nonrelativistic models, play an important role in the longitudinal response function.

Spin-isospin-dependent response function of nuclear matter at high excitation energies

Properties of the spin-isospin-dependent response function of nuclear matter at high excitation energies are investigated. Relativistic calculation of particle-hole and delta-hole propagation via meson exchange is done within the ring approximation. The excitation energies and widths of the pionic mode and the delta-hole collective mode are discussed. In particular, their implications for the high-energy ( 3He, t) reaction are studied.

Core polarization contribution to the nuclear matter response function in the quasi-elastic scattering region

The lowest order core polarization contribution to the nuclear response function, which is seen in the quasi-elastic electron scattering, is calculated in nuclear matter, using a finite range effective interaction with a tensor component. The relationship of our calculation with a sum rule approach is discussed. At this stage the fit with available experimental data is found not to be improved.