Theory Of Nuclear Matter Research Articles

Scalar field, nucleon structure and relativistic chiral theory for nuclear matter

Scalar field, nucleon structure and relativistic chiral theory for nuclear matter

Constraints on the Nuclear Symmetry Energy from Experiments, Theory and Observations

Nuclear mass measurements and neutron matter theory tightly constrain the nuclear symmetry energy parameters J, L, Ksym and Qsym . Corroboration of these constraints on J and L can be found from measurements of the neutron skin thicknesses and dipole polarizabilities of neutron-rich nuclei. The experimental constraints on these parameters are compared with those obtained from consideration of astrophysical measurements of the neutron star radius, which we show is highly correlated with L. Attention is aimed at the recent PREX and CREX neutron skin measurements from Jefferson Lab, NICER neutron star radius measurements, and a new interpretation of the GW170817 tidal deformability measurement. We find joint satisfaction of PREX and CREX gives J = 32.2 ± 1.7 MeV and L = 52.9 ± 13.2 MeV, in excellent agreement with neutron matter predictions of J = 32.0±1.1 MeV and L = 51.9±7.9 MeV.

Hadron-quark phase transition in neutron star by combining the relativistic Brueckner-Hartree-Fock theory and Dyson-Schwinger equation approach

Starting from the relativistic Brueckner-Hartree-Fock theory for nuclear matter and the Dyson-Schwinger equation approach for quark matter, the possible hadron-quark phase transition in the interior of a neutron star is explored. The first-order phase transition and crossover are studied by performing the Maxwell construction and three-window construction respectively. The mass-radius relation and the tidal deformability of the hybrid star are calculated and compared to the joint mass-radius observation of a neutron star and the constraints from gravitational wave detection. For the Maxwell construction, no stable quark core is found in the interior of a neutron star. For the three-window construction, the parameters of the smooth interpolation function are chosen in such a way to keep the thermodynamic stability and lead to a moderate crossover density region. To support a two-solar-mass neutron star under the three-window construction, the effective width of medium screening effects in quark matter should be around 0.35 GeV.

Constraints on Nuclear Symmetry Energy Parameters

A review is made of constraints on the nuclear symmetry energy parameters arising from nuclear binding energy measurements, theoretical chiral effective field predictions of neutron matter properties, the unitary gas conjecture, and measurements of neutron skin thicknesses and dipole polarizabilities. While most studies have been confined to the parameters SV and L, the important roles played by, and constraints on Ksym, or, equivalently, the neutron matter incompressibility KN, are discussed. Strong correlations among SV,L, and KN are found from both nuclear binding energies and neutron matter theory. However, these correlations somewhat differ in the two cases, and those from neutron matter theory have smaller uncertainties. To 68% confidence, it is found from neutron matter theory that SV=32.0±1.1 MeV, L=51.9±7.9 MeV and KN=152.2±38.1 MeV. Theoretical predictions for neutron skin thickness and dipole polarizability measurements of the neutron-rich nuclei 48Ca, 120Sn, and 208Pb are compared to recent experimental measurements, most notably the CREX and PREX neutron skin experiments from Jefferson Laboratory. By themselves, PREX I+II measurements of 208Pb and CREX measurement of 48Ca suggest L=121±47 MeV and L=−5±40 MeV, respectively, to 68% confidence. However, we show that nuclear interactions optimally satisfying both measurements imply L=53±13 MeV, nearly the range suggested by either nuclear mass measurements or neutron matter theory, and is also consistent with nuclear dipole polarizability measurements. This small parameter range implies R1.4=11.6±1.0 km and Λ1.4=228−90+148, which are consistent with NICER X-ray and LIGO/Virgo gravitational wave observations of neutron stars.

Equations of state for hot neutron stars-II. The role of exotic particle degrees of freedom

Explosive astrophysical systems - such as supernovae or compact star binary mergers - provide conditions where exotic degrees of freedom can be populated. Within the covariant density functional theory of nuclear matter we build several general purpose equations of state which, in addition to the baryonic octet, account for $\Delta(1232)$ resonance states. The thermodynamic stability of $\Delta$-admixed nuclear matter is investigated in the limiting case of vanishing temperature for charge fractions $Y_Q=0.01$ and $Y_Q=0.5$ and wide ranges of the coupling constants to the scalar and vector mesonic fields. General purpose equation of state models with exotica presently available on the \textsc{CompOSE} database are further reviewed; for a selection of them we then investigate thermal properties for thermodynamic conditions relevant for core-collapse supernovae and binary neutron star mergers. Modifications induced by hyperons, $\Delta(1232)$, $K^-$, pions and quarks are discussed.

Meson-exchange currents and superscaling analysis with relativistic effective mass of quasielastic electron scattering from C12

We reanalyze the scaling properties of inclusive quasielastic electron scattering from $^{12}\mathrm{C}$ by subtracting from the data the effects of two-particle emission. A model of relativistic meson-exchange currents (MEC) is employed within the mean field theory of nuclear matter, with scalar and vector potentials that induce an effective mass and a vector energy to the nucleons. A new phenomenological quasielastic scaling function is extracted from a selection of the data after the subtraction of the 2p-2h contribution. The resulting superscaling approach with relativistic effective mass (SuSAM*) can be used to compute the genuine quasielastic cross section without contamination of the 2p-2h channel that can then be added separately to obtain the total quasielastic plus two-nucleon emission response.

Δ-admixed neutron stars: Spinodal instabilities and dUrca processes

Within the covariant density functional theory of nuclear matter we build equations of state of Δ-admixed compact stars. Uncertainties in the interaction of Δ(1232) resonance states with nuclear matter, due to lack of experimental data, are accounted for by varying the coupling constants to scalar and vector mesonic fields. We find that, over a wide range of the parameter space allowed by nuclear physics experiments and astrophysical observations, cold catalyzed star matter exhibits a first order phase transition which persists also at finite temperature and out of β-equilibrium in the neutrino-transparent matter. Compact stars featuring such a phase transition in the outer core have small radii and, implicitly, tidal deformabilities. The parameter space is identified where simultaneously Δ-admixed compact stars obey the astrophysical constraint on maximum mass and allow for dUrca processes, which is otherwise forbidden.

Table of Stable Chemical Elements Based on the “Intensity—Compressibility Factor” Diagram and on Mean Square Fluctuations of Energy and Time

In this paper, a new physical notion, intensity, is introduced. The notion of intensity occurs in a special statistics, known as Gentile statistics, which is asymptotically close to ordinary thermodynamics. The introduction of the new notion of intensity in the theory of nuclear matter essentially changes the thermodynamical picture. Moreover, we can say that the thermodynamics of nuclear matter is the antipode of standard thermodynamics. On the basis of the "intensity--compressibility factor" diagram and mean square fluctuations of energy and time, a new table of properties of stable chemical elements is obtained and presented in this paper.

Medium-polarization effects in SD13 spin-triplet pairing

Stimulated by the still puzzling competition between spin-singlet and spin-triplet pairing in nuclei, the 3SD1 neutron-proton pairing is investigated in the framework of BCS theory of nuclear matter. The medium polarization effects are included in the single particle spectrum and also in the pairing interaction starting from the G-matrix, calculated in the Brueckner-Hartree-Fock approximation. The vertex corrections due to spin and isospin collective excitations of the medium are determined from the Bethe-Salpeter equation in the RPA limit, taking into account the tensor correlations. It is found that the self-energy corrections confine the superfluid state to very low-density, while remarkably quenching the magnitude of the energy gap, while the induced interaction has an attractive effect. The interplay between spin-singlet and spin-triplet pairing is discussed in nuclear matter as well as in finite nuclei.

The effective relativistic quantum field theory for nuclear matter with many‐body forces revisited

The quantum hydrodynamics (QHD) model with derivative parametric couplings represents, in this contribution, the starting point of our formulation. The striking aspect of this model is that it allows the theoretical simulation, through effective couplings, of the presence of many‐body forces in nuclear matter involving nonlinear meson self‐interaction and meson cross‐interaction terms in the scalar–isoscalar and scalar–isovector meson sectors. In this study, on the basis of the fundamental concept of naturalness in relativistic field theory, we extend the descriptive domain of the dynamics of the model to the vector–isoscalar and vector–isovector meson sectors. Among other topics, we discuss the connection of this theory with other known effective QHD models of the literature and its potentiality in describing a new physics for dense nuclear matter and neutron star matter.

Global superscaling analysis of quasielastic electron scattering with relativistic effective mass

We present a global analysis of the inclusive quasielastic electron scattering data with a superscaling approach with relativistic effective mass. The SuSAM* model exploits the approximation of factorization of the scaling function $f^*(\psi^*)$ out of the cross section under quasifree conditions. Our approach is based on the relativistic mean field theory of nuclear matter where a relativistic effective mass for the nucleon encodes the dynamics of nucleons moving in presence of scalar and vector potentials. Both the scaling variable $\psi^*$ and the single nucleon cross sections include the effective mass as a parameter to be fitted to the data alongside the Fermi momentum $k_F$. Several methods to extract the scaling function and its uncertainty from the data are proposed and compared. The model predictions for the quasielastic cross section and the theoretical error bands are presented and discussed for nuclei along the periodic table from $A=2$ to $A=238$: $^2$H, $^3$H, $^3$He, $^4$He, $^{12}$C, $^{6}$Li, $^{9}$Be, $^{24}$Mg, $^{59}$Ni, $^{89}$Y, $^{119}$Sn, $^{181}$Ta, $^{186}$W, $^{197}$Au, $^{16}$O, $^{27}$Al, $^{40}$Ca, $^{48}$Ca, $^{56}$Fe, $^{208}$Pb, and $^{238}$U. We find that more than 9000 of the total $\sim 20000$ data fall within the quasielastic theoretical bands. Predictions for $^{48}$Ti and $^{40}$Ar are also provided for the kinematics of interest to neutrino experiments.

Photons in dense nuclear matter: Random-phase approximation

We present a comprehensive and pedagogic discussion of the properties of photons in cold and dense nuclear matter based on the resummed one-loop photon self energy. Correlations between electrons, muons, protons and neutrons in beta equilibrium that arise due to electromagnetic and strong interactions are consistently taken into account within the random phase approximation. Screening effects and damping as well as collective excitations are systematically studied in a fully relativistic setup. Our study is relevant to linear response theory of dense nuclear matter, calculations of transport properties of cold dense matter and to investigations of the production and propagation of hypothetical vector bosons such as the dark photons.

Perturbation theory of nuclear matter with a microscopic effective interaction

An updated and improved version of the effective interaction based on the Argonne\textendash Urbana nuclear Hamiltonian\textemdash derived using the formalism of Correlated Basis Functions (CBF) and the cluster expansion technique\textemdash is employed to obtain a number of properties of cold nuclear matter at arbitrary neutron excess within the formalism of many-body perturbation theory. The numerical results\textemdash including the ground-state energy per nucleon, the symmetry energy, the pressure, the compressibility, and the single-particle spectrum\textemdash are discussed in the context of the available empirical information, obtained from measured nuclear properties and heavy-ion collisions.

Medium polarization and pairing in asymmetric nuclear matter

The many-body theory of asymmetric nuclear matter is developed beyond the Brueckner–Hartree–Fock approximation to incorporate the medium polarization effects. The extension is performed within the Babu–Brown induced interaction theory. After deriving the particle–hole interaction in the form of Landau–Migdal parameters, the effects of the induced component on the symmetry energy are investigated along with the screening of 1S0 proton–proton and 3PF2 neutron–neutron pairing, which are relevant for the neutron-star cooling. The crossover from repulsive (screening) to attractive (anti-screening) interaction going from pure neutron matter to symmetric nuclear matter is discussed.

A further update on possible crises in nuclear-matter theory

The ancient problem of the saturation of symmetric nuclear matter is reviewed with an update on the status of the crises that were identified at an early stage by John Clark. We discuss how the initial problem with variational calculations providing more binding than the two hole-line contribution for the same interaction was overcome by calculations including three hole-line contributions without however reproducing the empirical nuclear saturation properties. It is argued that this remaining problem is still open because many solutions have been proposed or ad hoc adjustments implemented without generating universal agreement on the proper interpretation of the physics. The problem of nuclear saturation therefore persists leading to the necessity of an analysis of the way the nuclear saturation properties are obtained from experimental data. We clarify the role of short-range correlations and review results for nuclear saturation when such ingredients are completely taken into account using the Green’s function method. The role of long-range correlations is then analyzed with special emphasis on the importance of attractive pion-dominated excitation modes which inevitably lead to higher saturation densities than observed. Because such modes have no counterpart in finite nuclear systems, it is therefore argued that they should not be considered when calculating nuclear matter properties. The remaining open question is then whether long-range correlations in finite nuclei which in turn have no counterpart in infinite matter, represent the remaining missing ingredient in this analysis. We also briefly comment on the role of three-body interactions in the context of the dispersive optical model description of experimental data. It is further noted that interactions based on chiral perturbation theory at present do not generate a sufficient number of high-momentum nucleons leading to radii that are too small and substantial overbinding in finite nuclei.

From holography towards real-world nuclear matter

Quantum chromodynamics is notoriously difficult to solve at nonzero baryon density, and most models or effective theories of dense quark or nuclear matter are restricted to a particular density regime and/or a particular form of matter. Here we study dense (and mostly cold) matter within the holographic Sakai-Sugimoto model, aiming at a strong-coupling framework in the wide density range between nuclear saturation density and ultra-high quark matter densities. The model contains only three parameters, and we ask whether it fulfills two basic requirements of real-world cold and dense matter, a first-order onset of nuclear matter and a chiral phase transition at high density to quark matter. Such a model would be extremely useful for astrophysical applications because it would provide a single equation of state for all densities relevant in a compact star. Our calculations are based on two approximations for baryonic matter, firstly an instanton gas and secondly a homogeneous ansatz for the non-abelian gauge fields on the flavor branes of the model. While the instanton gas shows chiral restoration at high densities but an unrealistic second-order baryon onset, the homogeneous ansatz behaves exactly the other way around. Our study thus provides all ingredients that are necessary for a more realistic model and allows for systematic improvements of the applied approximations.

Quantum relativistic transport theory for asymmetric nuclear matter: collective modes

Isospin, density and electromagnetic waves in asymmetric nuclear matter with the addition of electrons (ANM) are studied. The use of a semi classical relativistic approach based on the Wigner function and its Vlasov like equation to study ANM allowed to obtain the dispersion relations for small amplitude oscillations. The small longitudinal wave case results were equivalent with a previous work that used a somewhat different formalism called generating function. The small transverse wave results, that cannot be obtained directly using the generating function formalism, were also obtained.

Effective field theory for neutron stars with genuine many‐body forces

AbstractThe aim of our contribution is to shed some light on open questions facing the high density nuclear many‐body problem. We focus our attention on the conceptual issue of naturalness and its role for the baryon‐meson coupling for nuclear matter at high densities. As a guideline for the strengths of the various couplings the concept of naturalness has been adopted. In order to encourage possible new directions of research, we discuss relevant aspects of a relativistic effective theory for nuclear matter with “natural” parametric couplings and genuine many‐body forces. Among other topics, we discuss in this work the connection of this theory with other known effective Quantum Hadrodynamics (QHD) models found in literature and how we can potentially use our approach to describe new physics for neutron stars. We also show some preliminary results for the equation of state, population profiles and mass‐radius relation for neutron stars assuming local charge neutrality and beta equilibrium. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dirac-Brueckner-Hartree-Fock versus chiral effective field theory

We compare nuclear and neutron matter predictions based on two different ab initio approaches to nuclear forces and the nuclear many-body problem. The first consists of a realistic meson-theoretic nucleon-nucleon potential together with the relativistic counterpart of the Brueckner-Hartree-Fock theory of nuclear matter. The second is based on chiral effective field theory, with density-dependent interactions derived from leading order chiral three-nucleon forces. We find the results to be very close and conclude that both approaches contain important features governing the physics of nuclear and neutron matter.

AN EFFECTIVE THEORY FOR NUCLEAR MATTER WITH GENUINE MANY-BODY FORCES

Nuclear science has developed many excellent descriptions that embody various properties of the nucleus, and nuclear matter at low, medium and high densities. However, a full microscopic understanding of nuclear systems is still lacking. The aim of our theoretical research group is to shed some light on such challenges and particularly on open questions facing the high density nuclear many-body problem. Here we focus our attention on the conceptual issue of naturalness and its role in shaping the baryon-meson phase space dynamics in the description of the equation of state (EoS) of nuclear matter. In particular, in order to stimulate possible new directions of research, we discuss relevant aspects of a recently developed relativistic effective theory for nuclear matter with natural parametric couplings and genuine many-body forces. Among other topics we discuss in this work the connection of this theory with other known effective QHD models of the literature and its potentiality in describing a new physics for dense matter.