Nuclear Theory·nucl-th

Wednesday·June 15, 2016

8 papers—4 primary·4 cross-listed

01
Density dependence of the nuclear energy-density functional
Panagiota Papakonstantinou · Tae-Sun Park · Yeunhwan Lim · Chang Ho Hyun
The explicit density (rho) dependence in the coupling coefficients of the non-relativistic nuclear energy-density functional (EDF) encodes effects of three-nucleon forces and dynamical correlations. The necessity for a coupling coefficient in the form of a small fractional power of rho is empirical and the power often chosen arbitrarily. Consequently, precision-oriented parameterisations risk overfitting and loss of predictive power. Observing that the Fermi momentum kF~rho^1/3 is a key variable in Fermi systems, we examine if a power hierarchy in kF can be inferred from the properties of homogeneous matter in a domain of densities which is relevant for nuclear structure and neutron stars. For later applications we want to determine an EDF that is of good quality but not overtrained. We fit polynomial and other functions of rho^1/3 to existing microscopic calculations of the energy of symmetric and pure neutron matter and analyze the fits. We select a form and parameter set which we found robust and examine the parameters' naturalness and the resulting extrapolations. A statistical analysis confirms that low-order terms like rho^1/3 and rho^2/3 are the most relevant ones. It also hints at a different power hierarchy for symmetric vs. pure neutron matter, supporting the need for more than one rho^a terms in non-relativistic EDFs. The EDF we propose accommodates adopted properties of nuclear matter near saturation. Importantly, its extrapolation to dilute or asymmetric matter reproduces a range of existing microscopic results, to which it has not been fitted. It also predicts neutron-star properties consistent with observations. The coefficients display naturalness. Once determined for homogeneous matter, EDFs of the present form can be mapped onto Skyrme-type ones for use in nuclei. The statistical analysis can be extended to higher orders and for different ab initio calculations.
nucl-thPRC(2018)·55 citations
02
Nuclear in-medium effects on $η$ dynamics in proton-nucleus collisions
Jie Chen🇨🇳 · Zhao-Qing Feng🇨🇳 · Jian-Song Wang🇨🇳
The dynamics of $η$ meson produced in proton-induced nuclear reactions via the decay of N $^{*} (1535)$ has been investigated within the Lanzhou quantum molecular dynamics transport model (LQMD). The in-medium modifications of the $η$ production in dense nuclear matter are included in the model, in which an attractive $η$ -nucleon potential is implemented. The impact of the $η$ optical potential on the $η$ dynamics is investigated. It is found that the attractive potential leads to the reduction of high-momentum (kinetic energy) production from the spectra of momentum distributions and inclusive cross sections and increasing the reabsorption process by surrounding nucleons.
nucl-thNucl.Sci.Tech.(2016)·14 citations
03
Formation of Selfbound States in a One-Dimensional Nuclear Model -- A Renormalization Group based Density Functional Study
Sandra Kemler · Martin Pospiech · Jens Braun
In nuclear physics, Density Functional Theory (DFT) provides the basis for state-of-the art studies of ground-state properties of heavy nuclei. However, the direct relation of the density functional underlying these calculations and the microscopic nuclear forces is not yet fully understood. We present a combination of DFT and Renormalization Group (RG) techniques which allows to study selfbound many-body systems from microscopic interactions. We discuss its application with the aid of systems of identical fermions interacting via a long-range attractive and short-range repulsive two-body force in one dimension. We compute ground-state energies, intrinsic densities, and density correlation functions of these systems and compare our results to those obtained from other methods. In particular, we show how energies of excited states as well as the absolute square of the ground-state wave function can be extracted from the correlation functions within our approach. The relation between many-body perturbation theory and our DFT-RG approach is discussed and illustrated with the aid of the calculation of the second-order energy correction for a system of $N$ identical fermions interacting via a general two-body interaction. Moreover, we discuss the control of spuriously emerging fermion self-interactions in DFT studies within our framework. In general, our approach may help to guide the development of energy functionals for future quantitative DFT studies of heavy nuclei from microscopic interactions.
nucl-thcond-mat.othercond-mat.quant-gasJ.Phys.G(2017)·25 citations
04
Double-step truncation procedure for large-scale shell-model calculations
L. Coraggio · A. Gargano · N. Itaco
We present a procedure that is helpful to reduce the computational complexity of large-scale shell-model calculations, by preserving as much as possible the role of the rejected degrees of freedom in an effective approach. Our truncation is driven first by the analysis of the effective single-particle energies of the original large-scale shell-model hamiltonian, so to locate the relevant degrees of freedom to describe a class of isotopes or isotones, namely the single-particle orbitals that will constitute a new truncated model space. The second step is to perform an unitary transformation of the original hamiltonian from its model space into the truncated one. This transformation generates a new shell-model hamiltonian, defined in a smaller model space, that retains effectively the role of the excluded single-particle orbitals. As an application of this procedure, we have chosen a realistic shell-model hamiltonian defined in a large model space, set up by seven and five proton and neutron single-particle orbitals outside 88Sr, respectively. We study the dependence of shell-model results upon different truncations of the original model space for the Zr, Mo, Ru, Pd, Cd, and Sn isotopic chains, showing the reliability of this truncation procedure.
nucl-thPRC(2016)·26 citations
05
Mobile impurity in a Fermi sea from the functional renormalization group analytically continued to real time
Kazuhiko Kamikado · Takuya Kanazawa · Shun Uchino
Motivated by experiments with cold atoms, we investigate a mobile impurity immersed in a Fermi sea in three dimensions at zero temperature by means of the functional renormalization group. We first perform the derivative expansion of the effective action to calculate the ground state energy and Tan's contact across the polaron-molecule transition for several mass imbalances. Next we study quasiparticle properties of the impurity by using a real-time method recently developed in nuclear physics, which allows one to go beyond the derivative expansion. We obtain the spectral function of the polaron, the effective mass and quasiparticle weight of attractive and repulsive polarons, and clarify how they are affected by mass imbalances.
↳ cond-mat.quant-gasnucl-thPRA(2017)·21 citations
06
Stability of the pion string in a thermal and dense medium
Arjun Berera🇬🇧 · Robert Brandenberger🇨🇦 · Joel Mabillard🇬🇧 · Rudnei O. Ramos🇧🇷
We investigate the stability of the pion string in a thermal bath and a dense medium. We find that stability is dependent on the order of the chiral transition. String core stability within the experimentally allowed regime is found only if the chiral transition is second order, and even there the stable region is small, i.e., the temperature below which the core is unstable is close to the critical temperature of the phase transition. We also find that the presence of a dense medium, in addition to the thermal bath, enhances the experimentally accessible region with stable strings. We also argue that once the string core decays, the "effective winding" of the string persists at large distances from the string core. Our analysis is done both in the chiral limit, which is mainly what has been explored in the literature up to now, and for the physical $h \neq = 0$ case, where a conceptual framework is set up for addressing this regime and some simple estimates are done.
↳ hep-phhep-thnucl-thPRD(2016)·5 citations
07
Theoretical predictions of transverse kinematic imbalance in neutrino-nucleus interactions
Luke Pickering🇬🇧 · Xianguo Lu🇬🇧
Distributions of transverse kinematic imbalance in neutrino-nucleus interactions in the few GeV regime are sensitive to nuclear effects. We present a study comparing the latest predictions of transverse kinematic imbalance from the interaction simulations, NuWro and GENIE. We dis- cuss the differences between the model predictions.
↳ hep-phnucl-th6 citations
08
Gluonic Transversity from Lattice QCD
W. Detmold🇺🇸 · P. E. Shanahan🇺🇸
We present an exploratory study of the gluonic structure of the $ϕ$ meson using lattice QCD (LQCD). This includes the first investigation of gluonic transversity via the leading moment of the twist-two double-helicity-flip gluonic structure function $Δ (x, Q^{2})$ . This structure function only exists for targets of spin $J \geq 1$ and does not mix with quark distributions at leading twist, thereby providing a particularly clean probe of gluonic degrees of freedom. We also explore the gluonic analogue of the Soffer bound which relates the helicity flip and non-flip gluonic distributions, finding it to be saturated at the level of 80%. This work sets the stage for more complex LQCD studies of gluonic structure in the nucleon and in light nuclei where $Δ (x, Q^{2})$ is an 'exotic glue' observable probing gluons in a nucleus not associated with individual nucleons.
↳ hep-latnucl-thPRD(2016)·27 citations

Affiliations

first authorsco-authorsvia INSPIRE