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
06
Polyakov SU(3) extended linear $σ$ -model: Sixteen mesonic states in chiral phase-structure
Abdel Nasser Tawfik (Egyptian Ctr. Theor. Phys., Cairo and WLCAPP, Cairo)🇪🇬 · Abdel Magied Diab (Egyptian Ctr. Theor. Phys., Cairo and WLCAPP, Cairo)🇪🇬
The derivative of the grand potential in mean field approximation, non-strange and strange condensates and deconfinement phase-transition in thermal and dense hadronic medium are verified in extended SU(3) linear sigma-model (eLSM). In determining the chiral phase-transition, the chiral condensates sigma_x and sigma_y are analysed. The chiral mesonic phase-structures in temperature- and density-dependence are taken as free parameters to be fitted. These parameters are classified corresponding to scalar meson nonets; (pseudo)-scalar and (axial)-vector. For deconfinement phase-transition, effective Polyakov loop-potentials phi and phi^* are utilized. We investigated the in-medium effects on the masses of sixteen mesonic states states. The results are presented for two different forms for the effective Polyakov loop-potential and compared with other models with and without anomalous terms. The Polyakov loop potential in LSM has considerable effects on the chiral phase-transition in meson masses so that the restoration of the chiral symmetry becomes sharper and faster than LSM. We normalize all mesonic states with respect to the lowest Matsubara frequency. It has been found that the various mesonic states have different dissolving temperatures and chemical potentials, i.e. they survive the typically-averaged QCD phase boundary, defined by the QCD critical temperatures with varying chemical potentials. The thermal behavior of all meson masses has been investigated in the large- $N_{c}$ limit and found that the scalar meson masses are T-independent at large $N_{c}$ and high $T$ (except pi and sigma). For the pseudoscalar meson masses, the large N_c limit unifies the $T$ -dependence of all states in a universal bundle. The same is also observed for axial and axialvector meson masses in the large-N_c limit.
↳ hep-phhep-latnucl-thPRC(2015)·43 citations
07
Stoner ferromagnetism of a strongly interacting Fermi gas in the quasirepulsive regime
Lianyi He · Xia-Ji Liu · Xu-Guang Huang · Hui Hu
Recent advances in rapidly quenched ultracold atomic Fermi gases near a Feshbach resonance have brought about a number of interesting problems, in the context of observing the long-sought Stoner ferromagnetic phase transition. The possibility of experimentally obtaining a "quasirepulsive" regime in the upper branch of the energy spectrum due to the rapid quench is currently being debated, and the Stoner transition has mainly been investigated theoretically by using perturbation theory or at high polarization, due to the limited theoretical approaches in the strongly repulsive regime. In this work, we present a nonperturbative theoretical approach to the quasirepulsive upper branch of a Fermi gas near a broad Feshbach resonance, and we determine the finite-temperature phase diagram for the Stoner instability. Our results agree well with the known quantum Monte-Carlo simulations at zero temperature, and we recover the known virial expansion prediction at high temperature for arbitrary interaction strengths. At resonance, we find that the Stoner transition temperature becomes of the order of the Fermi temperature, around which the molecule formation rate becomes vanishingly small. This suggests a feasible way to observe Stoner ferromagnetism in the nondegenerate temperature regime.
↳ cond-mat.quant-gascond-mat.str-elnucl-thPRA(2016)·9 citations
08
QCD Factorization and PDFs from Lattice QCD Calculation
Yan-Qing Ma🇨🇳 · Jian-Wei Qiu🇺🇸
In this talk, we review a QCD factorization based approach to extract parton distribution and correlation functions from lattice QCD calculation of single hadron matrix elements of quark-gluon operators. We argue that although the lattice QCD calculations are done in the Euclidean space, the nonperturbative collinear behavior of the matrix elements are the same as that in the Minkowski space, and could be systematically factorized into parton distribution functions with infrared safe matching coefficients. The matching coefficients can be calculated perturbatively by applying the factorization formalism on to asymptotic partonic states.
↳ hep-phhep-latnucl-thInt.J.Mod.Phys.Conf.Ser.(2015)·57 citations
09
Electron-Ion Collider - taking us to the next QCD frontier
Jian-Wei Qiu🇺🇸
In this talk, I demonstrate that the proposed Electron-Ion Collider (EIC) will be an ideal and unique future facility to address many overarching questions about QCD and strong interaction physics at one place. The EIC will be the world's first polarized electron-proton (and light ion), as well as the first electron-nucleus collider at flexible collision energies. With its high luminosity and beam polarization, the EIC distinguishes itself from HERA and the other fixed target electron-hadron facilities around the world. The EIC is capable of taking us to the next QCD frontier to explore the glue that binds us all.
↳ hep-phnucl-exnucl-thInt.J.Mod.Phys.Conf.Ser.(2015)·0 citations

Affiliations

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