Nuclear Theory·nucl-th

Tuesday·December 9, 2014

9 papers—5 primary·4 cross-listed

01
Linear response of homogeneous nuclear matter with energy density functionals
A. Pastore🇧🇪 · D. Davesne🇫🇷 · J. Navarro🇪🇸
Response functions of infinite nuclear matter with arbitrary isospin asymmetry are studied in the framework of the random phase approximation. The residual interaction is derived from a general nuclear Skyrme energy density functional. Besides the usual central, spin-orbit and tensor terms it could also include other components as new density-dependent terms or three-body terms. Algebraic expressions for the response functions are obtained from the Bethe-Salpeter equation for the particle-hole propagator. Applications to symmetric nuclear matter, pure neutron matter and asymmetric nuclear matter are presented and discussed. Spin-isospin strength functions are analyzed for varying conditions of density, momentum transfer, isospin asymmetry, and temperature for some representative Skyrme functionals. Particular attention is paid to the discussion of instabilities, either real or unphysical, which could manifest in finite nuclei.
nucl-thPhys.Rept.(2014)·59 citations
02
Incoherent Pion Production in Neutrino - Deuteron Reactions
Jia-Jun Wu🇺🇸 · T. Sato🇯🇵 · T.-S. H. Lee🇺🇸
Within the multiple scattering formulation, the incoherent pion production in neutrino-deuteron reactions at energies near the $Δ (1232)$ resonance is investigated. The calculations include an impulse term and one-loop contributions from nucleon-nucleon ( $N N$ ) and pion-nucleon ( $π N$ ) final state interactions. The input amplitudes of $π N$ scattering and electroweak pion production reaction on nucleon are generated from a dynamical model which describes very extensive data of $π N$ scattering and both the electromagnetic and the weak pion production reactions on the nucleon. The $N N$ scattering amplitudes are generated from the Bonn potential. The validity of the calculational procedures is established by giving a reasonably good description of the data of pion photo-production on the deuteron. The constructed model is then applied to predict the cross sections of $ν + d \to μ^{-} + π^{+} + n + p$ and $ν + d \to μ^{-} + π^{0} + p + p$ reactions. The importance of including the $N N$ final state interactions to understand the experimental data of these neutrino-deuteron reactions is demonstrated. Our results strongly suggest that the spectator approximation used in the previous analyses to extract the pion production cross sections on the nucleon from the data on the deuteron is not valid for the $ν + d \to μ^{-} + π^{+} + n + p$ , but is a good approximation for $ν + d \to μ^{-} + π^{0} + p + p$ .
nucl-thhep-phPRC(2015)·48 citations
03
In-medium Spectral Functions in a Coarse-Graining Approach
Stephan Endres🇩🇪 · Hendrik van Hees🇩🇪 · Janus Weil🇩🇪 · Marcus Bleicher🇩🇪
We use a coarse-graining approach to extract local thermodynamic properties from simulations with a microscopic transport model by averaging over a large ensemble of events. Setting up a grid of small space-time cells and going into each cell's rest frame allows to determine baryon and energy density. With help of an equation of state we get the corresponding temperature $T$ and baryon-chemical potential $μ_{B}$ . These results are used for the calculation of the thermal dilepton yield. We apply and compare two different spectral functions for the $ρ$ meson, firstly a calculation from hadronic many-body theory and secondly a calculation from experimental scattering amplitudes. The results obtained with our approach are compared to measurements of the NA60 Collaboration. A relatively good description of the data is achieved with both spectral functions. However, the hadronic many-body calculation is found to be closer to the experimental data with regard to the in-medium broadening of the spectral shape.
nucl-thhep-phJ.Phys.Conf.Ser.(2015)·2 citations
04
Partial and quasi dynamical symmetries in quantum many-body systems
A. Leviatan
We introduce the notions of partial dynamical symmetry (PDS) and quasi dynamical symmetry (QDS) and demonstrate their relevance to nuclear spectroscopy, to quantum phase transitions and to mixed systems with regularity and chaos. The analysis serves to highlight the potential role of PDS and QDS towards understanding the emergent "simplicity out of complexity" exhibited by complex many-body systems.
nucl-thquant-phJ.Phys.Conf.Ser.(2015)·0 citations
05
Ab initio Bogoliubov coupled cluster theory for open-shell nuclei
Angelo Signoracci · Thomas Duguet · Gaute Hagen · Gustav Jansen
Ab initio many-body methods address closed-shell nuclei up to mass A ~ 130 on the basis of realistic two- and three-nucleon interactions. Several routes to address open-shell nuclei are currently under investigation, including ideas which exploit spontaneous symmetry breaking. Singly open-shell nuclei can be efficiently described via the sole breaking of $U (1)$ gauge symmetry associated with particle number conservation, to account for their superfluid character. The present work formulates and applies Bogoliubov coupled cluster (BCC) theory, which consists of representing the exact ground-state wavefunction of the system as the exponential of a quasiparticle excitation cluster operator acting on a Bogoliubov reference state. Equations for the ground-state energy and cluster amplitudes are derived at the singles and doubles level (BCCSD) both algebraically and diagrammatically. The formalism includes three-nucleon forces at the normal-ordered two-body level. The first BCC code is implemented in $m$ -scheme, which will eventually permit the treatment of doubly open-shell nuclei. Proof-of-principle calculations in an $N_{max} = 6$ spherical harmonic oscillator basis are performed for $^{16, 18, 20}$ O, $^{18}$ Ne, $^{20}$ Mg in the BCCD approximation with a chiral two-nucleon interaction, comparing to results obtained in standard coupled cluster theory when applicable. The breaking of $U (1)$ symmetry is monitored by computing the variance associated with the particle-number operator. The newly developed many-body formalism increases the potential span of ab initio calculations based on single-reference coupled cluster techniques tremendously, i.e. potentially to reach several hundred additional mid-mass nuclei. The new formalism offers a wealth of potential applications and further extensions dedicated to the description of ground and excited states of open-shell nuclei.
nucl-thPRC(2015)·79 citations

Affiliations

first authorsco-authorsvia INSPIRE

Linear response of homogeneous nuclear matter with energy density functionals

Incoherent Pion Production in Neutrino - Deuteron Reactions

In-medium Spectral Functions in a Coarse-Graining Approach

Partial and quasi dynamical symmetries in quantum many-body systems

Ab initio Bogoliubov coupled cluster theory for open-shell nuclei

Affiliations